Attachment 370913 Details for Bug 192890 – Patch for landing

[patch] Patch for landing

patch192890 (text/plain), 122.23 KB, created by Robin Morisset on 2019-05-29 20:01:54 PDT

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Creator: Robin Morisset

Created: 2019-05-29 20:01:54 PDT

Size: 122.23 KB

patch

obsolete

>diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
>index 60dbd77e533..0ef8ff452f5 100644
>--- a/Source/WebCore/ChangeLog
>+++ b/Source/WebCore/ChangeLog
>@@ -1,3 +1,116 @@
>+2019-05-29  Robin Morisset  <rmorisset@apple.com>
>+
>+        [WHLSL] Parsing and lexing the standard library is slow
>+        https://bugs.webkit.org/show_bug.cgi?id=192890
>+        <rdar://problem/50746335>
>+
>+        Reviewed by Myles Maxfield.
>+
>+        The main idea is to avoid backtracking by instead peeking at the next token (and occasionally at the one after that).
>+        This implies a few things:
>+        - We can replace the stack of tokens by a trivial ring buffer of size 2 (holding the next token and the one after, or WTF::nullopt if we are at the end of the file).
>+        - We now have "completeFooExpression" functions, to avoid having to reparse the prefix of some expression, if we find half-way through what it is.
>+
>+        I also fixed the following parser bug:
>+        - https://bugs.webkit.org/show_bug.cgi?id=198305 [WHLSL] Multiple variables with initializers in a declaration statement crashes the compiler
>+            which was due to a mistake I made in the grammar
>+
>+        Finally I added two new macros: CONSUME_TYPE and PARSE to eliminate about 500 lines of error propagation boilerplate.
>+
>+        There are still lots of ways of improving the parser and lexer, such as:
>+        - finishing the conversion of tokens in the lexer, not bothering with allocating string views
>+        - make two special tokens Invalid and EOF, to remove the overhead of Optional
>+        - make peekTypes and consumeTypes use templates to avoid constructing a Vector and calling find on it.
>+        - Turn the entire lexer into a proper automata, not going through the same characters again and again (this is certainly the largest win by far)
>+        - Remove the last few pieces of backtracking from the parser.
>+
>+        The current patch is already enough to make parsing the full standard library (something like 85k lines) approximately 260ms.
>+        This is still longer than I would like, but nowhere near the bottleneck any longer because of some other parts of the compiler.
>+
>+        * Modules/webgpu/WHLSL/WHLSLLexer.h:
>+        (WebCore::WHLSL::Lexer::Lexer):
>+        (WebCore::WHLSL::Lexer::consumeToken):
>+        (WebCore::WHLSL::Lexer::peek):
>+        (WebCore::WHLSL::Lexer::peekFurther):
>+        (WebCore::WHLSL::Lexer::state const):
>+        (WebCore::WHLSL::Lexer::setState):
>+        (WebCore::WHLSL::Lexer::unconsumeToken): Deleted.
>+        * Modules/webgpu/WHLSL/WHLSLParser.cpp:
>+        (WebCore::WHLSL::Parser::parse):
>+        (WebCore::WHLSL::Parser::peek):
>+        (WebCore::WHLSL::Parser::peekTypes):
>+        (WebCore::WHLSL::Parser::tryType):
>+        (WebCore::WHLSL::Parser::tryTypes):
>+        (WebCore::WHLSL::Parser::consumeTypes):
>+        (WebCore::WHLSL::Parser::parseConstantExpression):
>+        (WebCore::WHLSL::Parser::parseTypeArgument):
>+        (WebCore::WHLSL::Parser::parseTypeArguments):
>+        (WebCore::WHLSL::Parser::parseTypeSuffixAbbreviated):
>+        (WebCore::WHLSL::Parser::parseTypeSuffixNonAbbreviated):
>+        (WebCore::WHLSL::Parser::parseType):
>+        (WebCore::WHLSL::Parser::parseTypeDefinition):
>+        (WebCore::WHLSL::Parser::parseResourceSemantic):
>+        (WebCore::WHLSL::Parser::parseSpecializationConstantSemantic):
>+        (WebCore::WHLSL::Parser::parseStageInOutSemantic):
>+        (WebCore::WHLSL::Parser::parseSemantic):
>+        (WebCore::WHLSL::Parser::parseQualifiers):
>+        (WebCore::WHLSL::Parser::parseStructureElement):
>+        (WebCore::WHLSL::Parser::parseStructureDefinition):
>+        (WebCore::WHLSL::Parser::parseEnumerationDefinition):
>+        (WebCore::WHLSL::Parser::parseEnumerationMember):
>+        (WebCore::WHLSL::Parser::parseNativeTypeDeclaration):
>+        (WebCore::WHLSL::Parser::parseNumThreadsFunctionAttribute):
>+        (WebCore::WHLSL::Parser::parseAttributeBlock):
>+        (WebCore::WHLSL::Parser::parseParameter):
>+        (WebCore::WHLSL::Parser::parseParameters):
>+        (WebCore::WHLSL::Parser::parseFunctionDefinition):
>+        (WebCore::WHLSL::Parser::parseComputeFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseVertexFragmentFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseRegularFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseOperatorFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseNativeFunctionDeclaration):
>+        (WebCore::WHLSL::Parser::parseBlock):
>+        (WebCore::WHLSL::Parser::parseBlockBody):
>+        (WebCore::WHLSL::Parser::parseIfStatement):
>+        (WebCore::WHLSL::Parser::parseSwitchStatement):
>+        (WebCore::WHLSL::Parser::parseSwitchCase):
>+        (WebCore::WHLSL::Parser::parseForLoop):
>+        (WebCore::WHLSL::Parser::parseWhileLoop):
>+        (WebCore::WHLSL::Parser::parseDoWhileLoop):
>+        (WebCore::WHLSL::Parser::parseVariableDeclaration):
>+        (WebCore::WHLSL::Parser::parseVariableDeclarations):
>+        (WebCore::WHLSL::Parser::parseStatement):
>+        (WebCore::WHLSL::Parser::parseEffectfulExpression):
>+        (WebCore::WHLSL::Parser::parseEffectfulAssignment):
>+        (WebCore::WHLSL::Parser::parseExpression):
>+        (WebCore::WHLSL::Parser::parseTernaryConditional):
>+        (WebCore::WHLSL::Parser::completeTernaryConditional):
>+        (WebCore::WHLSL::Parser::parseAssignment):
>+        (WebCore::WHLSL::Parser::completeAssignment):
>+        (WebCore::WHLSL::Parser::parsePossibleTernaryConditional):
>+        (WebCore::WHLSL::Parser::parsePossibleLogicalBinaryOperation):
>+        (WebCore::WHLSL::Parser::completePossibleLogicalBinaryOperation):
>+        (WebCore::WHLSL::Parser::parsePossibleRelationalBinaryOperation):
>+        (WebCore::WHLSL::Parser::completePossibleRelationalBinaryOperation):
>+        (WebCore::WHLSL::Parser::parsePossibleShift):
>+        (WebCore::WHLSL::Parser::completePossibleShift):
>+        (WebCore::WHLSL::Parser::parsePossibleAdd):
>+        (WebCore::WHLSL::Parser::completePossibleAdd):
>+        (WebCore::WHLSL::Parser::parsePossibleMultiply):
>+        (WebCore::WHLSL::Parser::completePossibleMultiply):
>+        (WebCore::WHLSL::Parser::parsePossiblePrefix):
>+        (WebCore::WHLSL::Parser::parsePossibleSuffix):
>+        (WebCore::WHLSL::Parser::parseCallExpression):
>+        (WebCore::WHLSL::Parser::parseTerm):
>+        (WebCore::WHLSL::Parser::parseAddressSpaceType): Deleted.
>+        (WebCore::WHLSL::Parser::parseNonAddressSpaceType): Deleted.
>+        (WebCore::WHLSL::Parser::parseEntryPointFunctionDeclaration): Deleted.
>+        (WebCore::WHLSL::Parser::parseEffectfulPrefix): Deleted.
>+        (WebCore::WHLSL::Parser::parseEffectfulSuffix): Deleted.
>+        * Modules/webgpu/WHLSL/WHLSLParser.h:
>+        (WebCore::WHLSL::Parser::Error::dump const):
>+
> 2019-05-29  Jiewen Tan  <jiewen_tan@apple.com>
> 
>         Unreviewed, update WebAuthN to "Supported In Preview"
>diff --git a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLLexer.h b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLLexer.h
>index b08b477bc81..bbde9fe4f8b 100644
>--- a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLLexer.h
>+++ b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLLexer.h
>@@ -46,6 +46,8 @@ public:
>         : m_stringView(stringView)
>     {
>         skipWhitespaceAndComments();
>+        m_ringBuffer[0] = consumeTokenFromStream();
>+        m_ringBuffer[1] = consumeTokenFromStream();
>     }
> 
>     Lexer(const Lexer&) = delete;
>@@ -177,37 +179,57 @@ public:
> 
>     Optional<Token> consumeToken()
>     {
>-        if (!m_stack.isEmpty())
>-            return m_stack.takeLast();
>-        return consumeTokenFromStream();
>+        auto result = m_ringBuffer[m_ringBufferIndex];
>+        m_ringBuffer[m_ringBufferIndex] = consumeTokenFromStream();
>+        m_ringBufferIndex = (m_ringBufferIndex + 1) % 2;
>+        return result;
>     }
> 
>-    void unconsumeToken(Token&& token)
>+    Optional<Token> peek()
>     {
>-        m_stack.append(WTFMove(token));
>+        return m_ringBuffer[m_ringBufferIndex];
>     }
> 
>+    Optional<Token> peekFurther()
>+    {
>+        return m_ringBuffer[(m_ringBufferIndex + 1) % 2];
>+    }
>+
>+    // FIXME: We should not need this
>+    // https://bugs.webkit.org/show_bug.cgi?id=198357
>     struct State {
>-        Vector<Token> stack;
>+        Optional<Token> ringBuffer[2];
>+        unsigned ringBufferIndex;
>         unsigned offset;
>         unsigned lineNumber;
>     };
> 
>     State state() const
>     {
>-        return { m_stack, m_offset, m_lineNumber };
>+        State state;
>+        state.ringBuffer[0] = m_ringBuffer[0];
>+        state.ringBuffer[1] = m_ringBuffer[1];
>+        state.ringBufferIndex = m_ringBufferIndex;
>+        state.offset = m_offset;
>+        state.lineNumber = m_lineNumber;
>+        return state;
>     }
> 
>     void setState(const State& state)
>     {
>-        m_stack = state.stack;
>+        m_ringBuffer[0] = state.ringBuffer[0];
>+        m_ringBuffer[1] = state.ringBuffer[1];
>+        m_ringBufferIndex = state.ringBufferIndex;
>         m_offset = state.offset;
>         m_lineNumber = state.lineNumber;
>+
>     }
> 
>     void setState(State&& state)
>     {
>-        m_stack = WTFMove(state.stack);
>+        m_ringBuffer[0] = WTFMove(state.ringBuffer[0]);
>+        m_ringBuffer[1] = WTFMove(state.ringBuffer[1]);
>+        m_ringBufferIndex = WTFMove(state.ringBufferIndex);
>         m_offset = WTFMove(state.offset);
>         m_lineNumber = WTFMove(state.lineNumber);
>     }
>@@ -253,7 +275,8 @@ private:
>     Optional<unsigned> operatorName(unsigned) const;
> 
>     StringView m_stringView;
>-    Vector<Token> m_stack;
>+    Optional<Token> m_ringBuffer[2];
>+    unsigned m_ringBufferIndex { 0 };
>     unsigned m_offset { 0 };
>     unsigned m_lineNumber { 0 };
> };
>diff --git a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.cpp b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.cpp
>index 94752382fbe..00d74ead5bc 100644
>--- a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.cpp
>+++ b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.cpp
>@@ -38,6 +38,26 @@ namespace WebCore {
> 
> namespace WHLSL {
> 
>+#define PARSE(name, element, ...) \
>+    auto name = parse##element(__VA_ARGS__); \
>+    if (!name) \
>+        return Unexpected<Error>(name.error());
>+
>+#define CONSUME_TYPE(name, type) \
>+    auto name = consumeType(Lexer::Token::Type::type); \
>+    if (!name) \
>+        return Unexpected<Error>(name.error());
>+
>+#define PEEK(name) \
>+    auto name = peek(); \
>+    if (!name) \
>+        return Unexpected<Error>(name.error());
>+
>+#define PEEK_FURTHER(name) \
>+    auto name = peekFurther(); \
>+    if (!name) \
>+        return Unexpected<Error>(name.error());
>+
> // FIXME: https://bugs.webkit.org/show_bug.cgi?id=195682 Return a better error code from this, and report it to JavaScript.
> auto Parser::parse(Program& program, StringView stringView, Mode mode) -> Optional<Error>
> {
>@@ -45,87 +65,62 @@ auto Parser::parse(Program& program, StringView stringView, Mode mode) -> Option
>     m_mode = mode;
> 
>     while (!m_lexer.isFullyConsumed()) {
>-        if (tryType(Lexer::Token::Type::Semicolon)) {
>+        auto token = m_lexer.peek();
>+        if (!token)
>+            break;
>+        switch (token->type) {
>+        case Lexer::Token::Type::Semicolon:
>             m_lexer.consumeToken();
>             continue;
>+        case Lexer::Token::Type::Typedef: {
>+            auto typeDefinition = parseTypeDefinition();
>+            if (!typeDefinition)
>+                return typeDefinition.error();
>+            program.append(WTFMove(*typeDefinition));
>+            continue;
>         }
>-
>-        {
>-            auto typeDefinition = backtrackingScope<Expected<AST::TypeDefinition, Error>>([&]() {
>-                return parseTypeDefinition();
>-            });
>-            if (typeDefinition) {
>-                auto success = program.append(WTFMove(*typeDefinition));
>-                if (!success)
>-                    return WTF::nullopt;
>-                continue;
>-            }
>-        }
>-
>-        {
>-            auto structureDefinition = backtrackingScope<Expected<AST::StructureDefinition, Error>>([&]() {
>-                return parseStructureDefinition();
>-            });
>-            if (structureDefinition) {
>-                auto success = program.append(WTFMove(*structureDefinition));
>-                if (!success)
>-                    return WTF::nullopt;
>-                continue;
>-            }
>+        case Lexer::Token::Type::Struct: {
>+            auto structureDefinition = parseStructureDefinition();
>+            if (!structureDefinition)
>+                return structureDefinition.error();
>+            program.append(WTFMove(*structureDefinition));
>+            continue;
>         }
>-
>-        {
>-            auto enumerationDefinition = backtrackingScope<Expected<AST::EnumerationDefinition, Error>>([&]() {
>-                return parseEnumerationDefinition();
>-            });
>-            if (enumerationDefinition) {
>-                auto success = program.append(WTFMove(*enumerationDefinition));
>-                if (!success)
>-                    return WTF::nullopt;
>-                continue;
>-            }
>+        case Lexer::Token::Type::Enum: {
>+            auto enumerationDefinition = parseEnumerationDefinition();
>+            if (!enumerationDefinition)
>+                return enumerationDefinition.error();
>+            program.append(WTFMove(*enumerationDefinition));
>+            continue;
>         }
>-
>-        Optional<Error> error;
>-        {
>-            auto functionDefinition = backtrackingScope<Expected<AST::FunctionDefinition, Error>>([&]() {
>-                return parseFunctionDefinition();
>-            });
>-            if (functionDefinition) {
>-                auto success = program.append(WTFMove(*functionDefinition));
>-                if (!success)
>-                    return WTF::nullopt;
>+        case Lexer::Token::Type::Native: {
>+            ASSERT(m_mode == Mode::StandardLibrary);
>+            auto furtherToken = peekFurther();
>+            if (!furtherToken)
>+                return WTF::nullopt;
>+            if (furtherToken->type == Lexer::Token::Type::Typedef) {
>+                auto nativeTypeDeclaration = parseNativeTypeDeclaration();
>+                if (!nativeTypeDeclaration)
>+                    return nativeTypeDeclaration.error();
>+                program.append(WTFMove(*nativeTypeDeclaration));
>                 continue;
>             }
>-            error = functionDefinition.error();
>+            auto nativeFunctionDeclaration = parseNativeFunctionDeclaration();
>+            if (!nativeFunctionDeclaration)
>+                return nativeFunctionDeclaration.error();
>+            program.append(WTFMove(*nativeFunctionDeclaration));
>+            continue;
>         }
>-
>-        if (m_mode == Mode::StandardLibrary) {
>-            auto nativeFunctionDeclaration = backtrackingScope<Expected<AST::NativeFunctionDeclaration, Error>>([&]() {
>-                return parseNativeFunctionDeclaration();
>-            });
>-            if (nativeFunctionDeclaration) {
>-                auto success = program.append(WTFMove(*nativeFunctionDeclaration));
>-                if (!success)
>-                    return WTF::nullopt;
>-                continue;
>-            }
>+        default: {
>+            auto functionDefinition = parseFunctionDefinition();
>+            if (!functionDefinition)
>+                return functionDefinition.error();
>+            program.append(WTFMove(*functionDefinition));
>+            continue;
>         }
>-
>-        if (m_mode == Mode::StandardLibrary) {
>-            auto nativeTypeDeclaration = backtrackingScope<Expected<AST::NativeTypeDeclaration, Error>>([&]() {
>-                return parseNativeTypeDeclaration();
>-            });
>-            if (nativeTypeDeclaration) {
>-                auto success = program.append(WTFMove(*nativeTypeDeclaration));
>-                if (!success)
>-                    return WTF::nullopt;
>-                continue;
>-            }
>         }
>-
>-        return WTFMove(*error);
>     }
>+
>     return WTF::nullopt;
> }
> 
>@@ -140,29 +135,41 @@ auto Parser::fail(const String& message, TryToPeek tryToPeek) -> Unexpected<Erro
> 
> auto Parser::peek() -> Expected<Lexer::Token, Error>
> {
>-    if (auto token = m_lexer.consumeToken()) {
>-        m_lexer.unconsumeToken(Lexer::Token(*token));
>+    if (auto token = m_lexer.peek()) {
>         return *token;
>     }
>     return fail("Cannot consume token"_str, TryToPeek::No);
> }
> 
>+auto Parser::peekFurther() -> Expected<Lexer::Token, Error>
>+{
>+    if (auto token = m_lexer.peek()) {
>+        return *token;
>+    }
>+    return fail("Cannot consume two tokens"_str, TryToPeek::No);
>+}
>+
>+bool Parser::peekTypes(const Vector<Lexer::Token::Type>& types)
>+{
>+    if (auto token = m_lexer.peek())
>+        return std::find(types.begin(), types.end(), token->type) != types.end();
>+    return false;
>+}
>+
> Optional<Lexer::Token> Parser::tryType(Lexer::Token::Type type)
> {
>-    if (auto token = m_lexer.consumeToken()) {
>+    if (auto token = m_lexer.peek()) {
>         if (token->type == type)
>-            return token;
>-        m_lexer.unconsumeToken(Lexer::Token(*token));
>+            return m_lexer.consumeToken();
>     }
>     return WTF::nullopt;
> }
> 
>-Optional<Lexer::Token> Parser::tryTypes(Vector<Lexer::Token::Type> types)
>+Optional<Lexer::Token> Parser::tryTypes(const Vector<Lexer::Token::Type>& types)
> {
>-    if (auto token = m_lexer.consumeToken()) {
>+    if (auto token = m_lexer.peek()) {
>         if (std::find(types.begin(), types.end(), token->type) != types.end())
>-            return token;
>-        m_lexer.unconsumeToken(Lexer::Token(*token));
>+            return m_lexer.consumeToken();
>     }
>     return WTF::nullopt;
> }
>@@ -177,7 +184,7 @@ auto Parser::consumeType(Lexer::Token::Type type) -> Expected<Lexer::Token, Erro
>     return fail(makeString("Cannot consume token (expected ", Lexer::Token::typeName(type), ")"));
> }
> 
>-auto Parser::consumeTypes(Vector<Lexer::Token::Type> types) -> Expected<Lexer::Token, Error>
>+auto Parser::consumeTypes(const Vector<Lexer::Token::Type>& types) -> Expected<Lexer::Token, Error>
> {
>     auto buildExpectedString = [&]() -> String {
>         StringBuilder builder;
>@@ -367,12 +374,8 @@ auto Parser::parseConstantExpression() -> Expected<AST::ConstantExpression, Erro
>         return { AST::BooleanLiteral(WTFMove(*type), false) };
>     default: {
>         ASSERT(type->type == Lexer::Token::Type::Identifier);
>-        auto origin = consumeType(Lexer::Token::Type::FullStop);
>-        if (!origin)
>-            return Unexpected<Error>(origin.error());
>-        auto next = consumeType(Lexer::Token::Type::Identifier);
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        CONSUME_TYPE(origin, FullStop);
>+        CONSUME_TYPE(next, Identifier);
>         return { AST::EnumerationMemberLiteral(WTFMove(*origin), type->stringView.toString(), next->stringView.toString()) };
>     }
>     }
>@@ -380,55 +383,41 @@ auto Parser::parseConstantExpression() -> Expected<AST::ConstantExpression, Erro
> 
> auto Parser::parseTypeArgument() -> Expected<AST::TypeArgument, Error>
> {
>-    auto constantExpression = backtrackingScope<Expected<AST::ConstantExpression, Error>>([&]() {
>-        return parseConstantExpression();
>-    });
>-    if (constantExpression)
>+    PEEK(nextToken);
>+    PEEK_FURTHER(furtherToken);
>+    if (nextToken->type != Lexer::Token::Type::Identifier || furtherToken->type == Lexer::Token::Type::FullStop) {
>+        PARSE(constantExpression, ConstantExpression);
>         return AST::TypeArgument(WTFMove(*constantExpression));
>-    auto result = consumeType(Lexer::Token::Type::Identifier);
>-    if (!result)
>-        return Unexpected<Error>(result.error());
>+    }
>+    CONSUME_TYPE(result, Identifier);
>     return AST::TypeArgument(makeUniqueRef<AST::TypeReference>(Lexer::Token(*result), result->stringView.toString(), AST::TypeArguments()));
> }
> 
> auto Parser::parseTypeArguments() -> Expected<AST::TypeArguments, Error>
> {
>-    auto typeArguments = backtrackingScope<Optional<AST::TypeArguments>>([&]() -> Optional<AST::TypeArguments> {
>-        auto lessThanSign = consumeType(Lexer::Token::Type::LessThanSign);
>-        if (!lessThanSign)
>-            return WTF::nullopt;
>-        AST::TypeArguments typeArguments;
>-        auto typeArgument = parseTypeArgument();
>-        if (!typeArgument)
>-            return WTF::nullopt;
>-        typeArguments.append(WTFMove(*typeArgument));
>-        while (tryType(Lexer::Token::Type::Comma)) {
>-            auto typeArgument = parseTypeArgument();
>-            if (!typeArgument)
>-                return WTF::nullopt;
>-            typeArguments.append(WTFMove(*typeArgument));
>-        }
>-        auto greaterThanSign = consumeType(Lexer::Token::Type::GreaterThanSign);
>-        if (!greaterThanSign)
>-            return WTF::nullopt;
>+    AST::TypeArguments typeArguments;
>+    auto lessThanSign = tryType(Lexer::Token::Type::LessThanSign);
>+    if (!lessThanSign)
>         return typeArguments;
>-    });
>-    if (typeArguments)
>-        return WTFMove(*typeArguments);
> 
>-    typeArguments = backtrackingScope<Optional<AST::TypeArguments>>([&]() -> Optional<AST::TypeArguments> {
>-        auto lessThanSign = consumeType(Lexer::Token::Type::LessThanSign);
>-        if (!lessThanSign)
>-            return WTF::nullopt;
>-        auto greaterThanSign = consumeType(Lexer::Token::Type::GreaterThanSign);
>-        if (!greaterThanSign)
>-            return WTF::nullopt;
>-        return {{ }};
>-    });
>-    if (typeArguments)
>-        return WTFMove(*typeArguments);
>+    auto greaterThanSign = tryType(Lexer::Token::Type::GreaterThanSign);
>+    if (greaterThanSign)
>+        return typeArguments;
>+
>+    PARSE(typeArgument, TypeArgument);
>+    typeArguments.append(WTFMove(*typeArgument));
>+
>+    while (true) {
>+        auto greaterThanSign = tryType(Lexer::Token::Type::GreaterThanSign);
>+        if (greaterThanSign)
>+            break;
> 
>-    return AST::TypeArguments();
>+        CONSUME_TYPE(comma, Comma);
>+        PARSE(typeArgument, TypeArgument);
>+        typeArguments.append(WTFMove(*typeArgument));
>+    }
>+
>+    return typeArguments;
> }
> 
> auto Parser::parseTypeSuffixAbbreviated() -> Expected<TypeSuffixAbbreviated, Error>
>@@ -440,9 +429,7 @@ auto Parser::parseTypeSuffixAbbreviated() -> Expected<TypeSuffixAbbreviated, Err
>         auto numElements = consumeNonNegativeIntegralLiteral();
>         if (!numElements)
>             return Unexpected<Error>(numElements.error());
>-        auto rightSquareBracket = consumeType(Lexer::Token::Type::RightSquareBracket);
>-        if (!rightSquareBracket)
>-            return Unexpected<Error>(rightSquareBracket.error());
>+        CONSUME_TYPE(rightSquareBracket, RightSquareBracket);
>         return {{ *token, *numElements }};
>     }
>     return {{ *token, WTF::nullopt }};
>@@ -457,9 +444,7 @@ auto Parser::parseTypeSuffixNonAbbreviated() -> Expected<TypeSuffixNonAbbreviate
>         auto numElements = consumeNonNegativeIntegralLiteral();
>         if (!numElements)
>             return Unexpected<Error>(numElements.error());
>-        auto rightSquareBracket = consumeType(Lexer::Token::Type::RightSquareBracket);
>-        if (!rightSquareBracket)
>-            return Unexpected<Error>(rightSquareBracket.error());
>+        CONSUME_TYPE(rightSquareBracket, RightSquareBracket);
>         return {{ *token, WTF::nullopt, *numElements }};
>     }
>     auto addressSpaceToken = consumeTypes({ Lexer::Token::Type::Constant, Lexer::Token::Type::Device, Lexer::Token::Type::Threadgroup, Lexer::Token::Type::Thread});
>@@ -484,78 +469,60 @@ auto Parser::parseTypeSuffixNonAbbreviated() -> Expected<TypeSuffixNonAbbreviate
>     return {{ *token, { addressSpace }, WTF::nullopt }};
> }
> 
>-auto Parser::parseAddressSpaceType() -> Expected<UniqueRef<AST::UnnamedType>, Error>
>+auto Parser::parseType() -> Expected<UniqueRef<AST::UnnamedType>, Error>
> {
>-    auto addressSpaceToken = consumeTypes({ Lexer::Token::Type::Constant, Lexer::Token::Type::Device, Lexer::Token::Type::Threadgroup, Lexer::Token::Type::Thread});
>-    if (!addressSpaceToken)
>-        return Unexpected<Error>(addressSpaceToken.error());
>-    AST::AddressSpace addressSpace;
>-    switch (addressSpaceToken->type) {
>-    case Lexer::Token::Type::Constant:
>-        addressSpace = AST::AddressSpace::Constant;
>-        break;
>-    case Lexer::Token::Type::Device:
>-        addressSpace = AST::AddressSpace::Device;
>-        break;
>-    case Lexer::Token::Type::Threadgroup:
>-        addressSpace = AST::AddressSpace::Threadgroup;
>-        break;
>-    default:
>-        ASSERT(addressSpaceToken->type == Lexer::Token::Type::Thread);
>-        addressSpace = AST::AddressSpace::Thread;
>-        break;
>-    }
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-    auto typeArguments = parseTypeArguments();
>-    if (!typeArguments)
>-        return Unexpected<Error>(typeArguments.error());
>+    auto addressSpaceToken = tryTypes({ Lexer::Token::Type::Constant, Lexer::Token::Type::Device, Lexer::Token::Type::Threadgroup, Lexer::Token::Type::Thread});
> 
>-    auto constructTypeFromSuffixAbbreviated = [&](const TypeSuffixAbbreviated& typeSuffixAbbreviated, UniqueRef<AST::UnnamedType>&& previous) -> UniqueRef<AST::UnnamedType> {
>-        switch (typeSuffixAbbreviated.token.type) {
>-        case Lexer::Token::Type::Star:
>-            return { makeUniqueRef<AST::PointerType>(Lexer::Token(typeSuffixAbbreviated.token), addressSpace, WTFMove(previous)) };
>-        case Lexer::Token::Type::SquareBracketPair:
>-            return { makeUniqueRef<AST::ArrayReferenceType>(Lexer::Token(typeSuffixAbbreviated.token), addressSpace, WTFMove(previous)) };
>-        default:
>-            ASSERT(typeSuffixAbbreviated.token.type == Lexer::Token::Type::LeftSquareBracket);
>-            return { makeUniqueRef<AST::ArrayType>(Lexer::Token(typeSuffixAbbreviated.token), WTFMove(previous), *typeSuffixAbbreviated.numElements) };
>-        }
>-    };
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(typeArguments, TypeArguments);
> 
>-    auto firstTypeSuffixAbbreviated = parseTypeSuffixAbbreviated();
>-    if (!firstTypeSuffixAbbreviated)
>-        return Unexpected<Error>(firstTypeSuffixAbbreviated.error());
>-    UniqueRef<AST::UnnamedType> result = makeUniqueRef<AST::TypeReference>(WTFMove(*addressSpaceToken), name->stringView.toString(), WTFMove(*typeArguments));
>-    auto next = constructTypeFromSuffixAbbreviated(*firstTypeSuffixAbbreviated, WTFMove(result));
>-    result = WTFMove(next);
>-    while (true) {
>-        auto typeSuffixAbbreviated = backtrackingScope<Expected<TypeSuffixAbbreviated, Error>>([&]() {
>-            return parseTypeSuffixAbbreviated();
>-        });
>-        if (!typeSuffixAbbreviated)
>+    if (addressSpaceToken) {
>+        AST::AddressSpace addressSpace;
>+        switch (addressSpaceToken->type) {
>+        case Lexer::Token::Type::Constant:
>+            addressSpace = AST::AddressSpace::Constant;
>             break;
>-        // FIXME: The nesting here might be in the wrong order.
>-        next = constructTypeFromSuffixAbbreviated(*typeSuffixAbbreviated, WTFMove(result));
>+        case Lexer::Token::Type::Device:
>+            addressSpace = AST::AddressSpace::Device;
>+            break;
>+        case Lexer::Token::Type::Threadgroup:
>+            addressSpace = AST::AddressSpace::Threadgroup;
>+            break;
>+        default:
>+            ASSERT(addressSpaceToken->type == Lexer::Token::Type::Thread);
>+            addressSpace = AST::AddressSpace::Thread;
>+            break;
>+        }
>+        auto constructTypeFromSuffixAbbreviated = [&](const TypeSuffixAbbreviated& typeSuffixAbbreviated, UniqueRef<AST::UnnamedType>&& previous) -> UniqueRef<AST::UnnamedType> {
>+            switch (typeSuffixAbbreviated.token.type) {
>+            case Lexer::Token::Type::Star:
>+                return { makeUniqueRef<AST::PointerType>(Lexer::Token(typeSuffixAbbreviated.token), addressSpace, WTFMove(previous)) };
>+            case Lexer::Token::Type::SquareBracketPair:
>+                return { makeUniqueRef<AST::ArrayReferenceType>(Lexer::Token(typeSuffixAbbreviated.token), addressSpace, WTFMove(previous)) };
>+            default:
>+                ASSERT(typeSuffixAbbreviated.token.type == Lexer::Token::Type::LeftSquareBracket);
>+                return { makeUniqueRef<AST::ArrayType>(Lexer::Token(typeSuffixAbbreviated.token), WTFMove(previous), *typeSuffixAbbreviated.numElements) };
>+            }
>+        };
>+        PARSE(firstTypeSuffixAbbreviated, TypeSuffixAbbreviated);
>+        UniqueRef<AST::UnnamedType> result = makeUniqueRef<AST::TypeReference>(WTFMove(*addressSpaceToken), name->stringView.toString(), WTFMove(*typeArguments));
>+        auto next = constructTypeFromSuffixAbbreviated(*firstTypeSuffixAbbreviated, WTFMove(result));
>         result = WTFMove(next);
>+        while (true) {
>+            PEEK(nextToken);
>+            if (nextToken->type != Lexer::Token::Type::Star
>+                && nextToken->type != Lexer::Token::Type::SquareBracketPair
>+                && nextToken->type != Lexer::Token::Type::LeftSquareBracket) {
>+                break;
>+            }
>+            PARSE(typeSuffixAbbreviated, TypeSuffixAbbreviated);
>+            // FIXME: The nesting here might be in the wrong order.
>+            next = constructTypeFromSuffixAbbreviated(*typeSuffixAbbreviated, WTFMove(result));
>+            result = WTFMove(next);
>+        }
>+        return WTFMove(result);
>     }
> 
>-    return WTFMove(result);
>-}
>-
>-auto Parser::parseNonAddressSpaceType() -> Expected<UniqueRef<AST::UnnamedType>, Error>
>-{
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-    auto typeArguments = parseTypeArguments();
>-    if (!typeArguments)
>-        return Unexpected<Error>(typeArguments.error());
>-
>     auto constructTypeFromSuffixNonAbbreviated = [&](const TypeSuffixNonAbbreviated& typeSuffixNonAbbreviated, UniqueRef<AST::UnnamedType>&& previous) -> UniqueRef<AST::UnnamedType> {
>         switch (typeSuffixNonAbbreviated.token.type) {
>         case Lexer::Token::Type::Star:
>@@ -567,58 +534,29 @@ auto Parser::parseNonAddressSpaceType() -> Expected<UniqueRef<AST::UnnamedType>,
>             return { makeUniqueRef<AST::ArrayType>(Lexer::Token(typeSuffixNonAbbreviated.token), WTFMove(previous), *typeSuffixNonAbbreviated.numElements) };
>         }
>     };
>-
>-    UniqueRef<AST::UnnamedType> result = makeUniqueRef<AST::TypeReference>(WTFMove(*origin), name->stringView.toString(), WTFMove(*typeArguments));
>+    UniqueRef<AST::UnnamedType> result = makeUniqueRef<AST::TypeReference>(WTFMove(*name), name->stringView.toString(), WTFMove(*typeArguments));
>     while (true) {
>-        auto typeSuffixNonAbbreviated = backtrackingScope<Expected<TypeSuffixNonAbbreviated, Error>>([&]() {
>-            return parseTypeSuffixNonAbbreviated();
>-        });
>-        if (!typeSuffixNonAbbreviated)
>+        PEEK(nextToken);
>+        if (nextToken->type != Lexer::Token::Type::Star
>+            && nextToken->type != Lexer::Token::Type::SquareBracketPair
>+            && nextToken->type != Lexer::Token::Type::LeftSquareBracket) {
>             break;
>+        }
>+        PARSE(typeSuffixNonAbbreviated, TypeSuffixNonAbbreviated);
>         // FIXME: The nesting here might be in the wrong order.
>         auto next = constructTypeFromSuffixNonAbbreviated(*typeSuffixNonAbbreviated, WTFMove(result));
>         result = WTFMove(next);
>     }
>-
>     return WTFMove(result);
> }
> 
>-auto Parser::parseType() -> Expected<UniqueRef<AST::UnnamedType>, Error>
>-{
>-    {
>-        auto type = backtrackingScope<Expected<UniqueRef<AST::UnnamedType>, Error>>([&]() {
>-            return parseAddressSpaceType();
>-        });
>-        if (type)
>-            return type;
>-    }
>-
>-    auto type = backtrackingScope<Expected<UniqueRef<AST::UnnamedType>, Error>>([&]() {
>-        return parseNonAddressSpaceType();
>-    });
>-    if (type)
>-        return type;
>-
>-    return Unexpected<Error>(type.error());
>-}
>-
> auto Parser::parseTypeDefinition() -> Expected<AST::TypeDefinition, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Typedef);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-    auto equals = consumeType(Lexer::Token::Type::EqualsSign);
>-    if (!equals)
>-        return Unexpected<Error>(equals.error());
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>-    auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-    if (!semicolon)
>-        return Unexpected<Error>(semicolon.error());
>+    CONSUME_TYPE(origin, Typedef);
>+    CONSUME_TYPE(name, Identifier);
>+    CONSUME_TYPE(equals, EqualsSign);
>+    PARSE(type, Type);
>+    CONSUME_TYPE(semicolon, Semicolon);
>     return AST::TypeDefinition(WTFMove(*origin), name->stringView.toString(), WTFMove(*type));
> }
> 
>@@ -681,17 +619,10 @@ auto Parser::parseBuiltInSemantic() -> Expected<AST::BuiltInSemantic, Error>
> 
> auto Parser::parseResourceSemantic() -> Expected<AST::ResourceSemantic, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Register);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    CONSUME_TYPE(origin, Register);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
> 
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>-    auto info = consumeType(Lexer::Token::Type::Identifier);
>-    if (!info)
>-        return Unexpected<Error>(info.error());
>+    CONSUME_TYPE(info, Identifier);
>     if (info->stringView.length() < 2 || (info->stringView[0] != 'u'
>         && info->stringView[0] != 't'
>         && info->stringView[0] != 'b'
>@@ -720,9 +651,7 @@ auto Parser::parseResourceSemantic() -> Expected<AST::ResourceSemantic, Error>
> 
>     unsigned space = 0;
>     if (tryType(Lexer::Token::Type::Comma)) {
>-        auto spaceToken = consumeType(Lexer::Token::Type::Identifier);
>-        if (!spaceToken)
>-            return Unexpected<Error>(spaceToken.error());
>+        CONSUME_TYPE(spaceToken, Identifier);
>         auto prefix = "space"_str;
>         if (!spaceToken->stringView.startsWith(StringView(prefix)))
>             return Unexpected<Error>(Error(makeString("Second argument to resource semantic ", spaceToken->stringView, " needs be of the form 'space0'")));
>@@ -734,175 +663,113 @@ auto Parser::parseResourceSemantic() -> Expected<AST::ResourceSemantic, Error>
>         space = *spaceValue;
>     }
> 
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>     return AST::ResourceSemantic(WTFMove(*origin), mode, *index, space);
> }
> 
> auto Parser::parseSpecializationConstantSemantic() -> Expected<AST::SpecializationConstantSemantic, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Specialized);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    CONSUME_TYPE(origin, Specialized);
>     return AST::SpecializationConstantSemantic(WTFMove(*origin));
> }
> 
> auto Parser::parseStageInOutSemantic() -> Expected<AST::StageInOutSemantic, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Attribute);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>+    CONSUME_TYPE(origin, Attribute);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
> 
>     auto index = consumeNonNegativeIntegralLiteral();
>     if (!index)
>         return Unexpected<Error>(index.error());
> 
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>     return AST::StageInOutSemantic(WTFMove(*origin), *index);
> }
> 
>-auto Parser::parseSemantic() -> Expected<AST::Semantic, Error>
>+auto Parser::parseSemantic() -> Expected<Optional<AST::Semantic>, Error>
> {
>-    auto builtInSemantic = backtrackingScope<Expected<AST::BuiltInSemantic, Error>>([&]() {
>-        return parseBuiltInSemantic();
>-    });
>-    if (builtInSemantic)
>-        return AST::Semantic(WTFMove(*builtInSemantic));
>-
>-    auto resourceSemantic = backtrackingScope<Expected<AST::ResourceSemantic, Error>>([&]() {
>-        return parseResourceSemantic();
>-    });
>-    if (resourceSemantic)
>-        return AST::Semantic(WTFMove(*resourceSemantic));
>-
>-    auto specializationConstantSemantic = backtrackingScope<Expected<AST::SpecializationConstantSemantic, Error>>([&]() {
>-        return parseSpecializationConstantSemantic();
>-    });
>-    if (specializationConstantSemantic)
>-        return AST::Semantic(WTFMove(*specializationConstantSemantic));
>-
>-    auto stageInOutSemantic = backtrackingScope<Expected<AST::StageInOutSemantic, Error>>([&]() {
>-        return parseStageInOutSemantic();
>-    });
>-    if (stageInOutSemantic)
>-        return AST::Semantic(WTFMove(*stageInOutSemantic));
>+    if (!tryType(Lexer::Token::Type::Colon))
>+        return { WTF::nullopt };
> 
>-    return Unexpected<Error>(stageInOutSemantic.error());
>+    PEEK(token);
>+    switch (token->type) {
>+    case Lexer::Token::Type::Attribute: {
>+        PARSE(result, StageInOutSemantic);
>+        return { AST::Semantic(WTFMove(*result)) };
>+    }
>+    case Lexer::Token::Type::Specialized:  {
>+        PARSE(result, SpecializationConstantSemantic);
>+        return { AST::Semantic(WTFMove(*result)) };
>+    }
>+    case Lexer::Token::Type::Register:  {
>+        PARSE(result, ResourceSemantic);
>+        return { AST::Semantic(WTFMove(*result)) };
>+    }
>+    default:  {
>+        PARSE(result, BuiltInSemantic);
>+        return { AST::Semantic(WTFMove(*result)) };
>+    }
>+    }
> }
> AST::Qualifiers Parser::parseQualifiers()
> {
>     AST::Qualifiers qualifiers;
>-    while (true) {
>-        if (auto next = tryType(Lexer::Token::Type::Qualifier)) {
>-            if ("nointerpolation" == next->stringView)
>-                qualifiers.append(AST::Qualifier::Nointerpolation);
>-            else if ("noperspective" == next->stringView)
>-                qualifiers.append(AST::Qualifier::Noperspective);
>-            else if ("uniform" == next->stringView)
>-                qualifiers.append(AST::Qualifier::Uniform);
>-            else if ("centroid" == next->stringView)
>-                qualifiers.append(AST::Qualifier::Centroid);
>-            else {
>-                ASSERT("sample" == next->stringView);
>-                qualifiers.append(AST::Qualifier::Sample);
>-            }
>-        } else
>-            break;
>+    while (auto next = tryType(Lexer::Token::Type::Qualifier)) {
>+        if ("nointerpolation" == next->stringView)
>+            qualifiers.append(AST::Qualifier::Nointerpolation);
>+        else if ("noperspective" == next->stringView)
>+            qualifiers.append(AST::Qualifier::Noperspective);
>+        else if ("uniform" == next->stringView)
>+            qualifiers.append(AST::Qualifier::Uniform);
>+        else if ("centroid" == next->stringView)
>+            qualifiers.append(AST::Qualifier::Centroid);
>+        else {
>+            ASSERT("sample" == next->stringView);
>+            qualifiers.append(AST::Qualifier::Sample);
>+        }
>     }
>     return qualifiers;
> }
> 
> auto Parser::parseStructureElement() -> Expected<AST::StructureElement, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>     AST::Qualifiers qualifiers = parseQualifiers();
> 
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>-
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>+    PARSE(type, Type);
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(semantic, Semantic);
>+    CONSUME_TYPE(semicolon, Semicolon);
> 
>-        auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-        if (!semicolon)
>-            return Unexpected<Error>(semicolon.error());
>-
>-        return AST::StructureElement(WTFMove(*origin), WTFMove(qualifiers), WTFMove(*type), name->stringView.toString(), WTFMove(*semantic));
>-    }
>-
>-    auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-    if (!semicolon)
>-        return Unexpected<Error>(semicolon.error());
>-
>-    return AST::StructureElement(WTFMove(*origin), WTFMove(qualifiers), WTFMove(*type), name->stringView.toString(), WTF::nullopt);
>+    return AST::StructureElement(WTFMove(*origin), WTFMove(qualifiers), WTFMove(*type), name->stringView.toString(), WTFMove(*semantic));
> }
> 
> auto Parser::parseStructureDefinition() -> Expected<AST::StructureDefinition, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Struct);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-
>-    auto leftCurlyBracket = consumeType(Lexer::Token::Type::LeftCurlyBracket);
>-    if (!leftCurlyBracket)
>-        return Unexpected<Error>(leftCurlyBracket.error());
>+    CONSUME_TYPE(origin, Struct);
>+    CONSUME_TYPE(name, Identifier);
>+    CONSUME_TYPE(leftCurlyBracket, LeftCurlyBracket);
> 
>     AST::StructureElements structureElements;
>-    while (true) {
>-        auto structureElement = backtrackingScope<Expected<AST::StructureElement, Error>>([&]() {
>-            return parseStructureElement();
>-        });
>-        if (structureElement)
>-            structureElements.append(WTFMove(*structureElement));
>-        else
>-            break;
>+    while (!tryType(Lexer::Token::Type::RightCurlyBracket)) {
>+        PARSE(structureElement, StructureElement);
>+        structureElements.append(WTFMove(*structureElement));
>     }
> 
>-    auto rightCurlyBracket = consumeType(Lexer::Token::Type::RightCurlyBracket);
>-    if (!rightCurlyBracket)
>-        return Unexpected<Error>(rightCurlyBracket.error());
>-
>     return AST::StructureDefinition(WTFMove(*origin), name->stringView.toString(), WTFMove(structureElements));
> }
> 
> auto Parser::parseEnumerationDefinition() -> Expected<AST::EnumerationDefinition, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Enum);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>+    CONSUME_TYPE(origin, Enum);
>+    CONSUME_TYPE(name, Identifier);
> 
>     auto type = ([&]() -> Expected<UniqueRef<AST::UnnamedType>, Error> {
>         if (tryType(Lexer::Token::Type::Colon)) {
>-            auto parsedType = parseType();
>-            if (!parsedType)
>-                return Unexpected<Error>(parsedType.error());
>+            PARSE(parsedType, Type);
>             return WTFMove(*parsedType);
>         }
>         return { makeUniqueRef<AST::TypeReference>(Lexer::Token(*origin), "int"_str, AST::TypeArguments()) };
>@@ -910,13 +777,9 @@ auto Parser::parseEnumerationDefinition() -> Expected<AST::EnumerationDefinition
>     if (!type)
>         return Unexpected<Error>(type.error());
> 
>-    auto leftCurlyBracket = consumeType(Lexer::Token::Type::LeftCurlyBracket);
>-    if (!leftCurlyBracket)
>-        return Unexpected<Error>(leftCurlyBracket.error());
>+    CONSUME_TYPE(leftCurlyBracket, LeftCurlyBracket);
> 
>-    auto firstEnumerationMember = parseEnumerationMember();
>-    if (!firstEnumerationMember)
>-        return Unexpected<Error>(firstEnumerationMember.error());
>+    PARSE(firstEnumerationMember, EnumerationMember);
> 
>     AST::EnumerationDefinition result(WTFMove(*origin), name->stringView.toString(), WTFMove(*type));
>     auto success = result.add(WTFMove(*firstEnumerationMember));
>@@ -924,32 +787,24 @@ auto Parser::parseEnumerationDefinition() -> Expected<AST::EnumerationDefinition
>         return fail("Cannot add enumeration member"_str);
> 
>     while (tryType(Lexer::Token::Type::Comma)) {
>-        auto member = parseEnumerationMember();
>-        if (!member)
>-            return Unexpected<Error>(member.error());
>+        PARSE(member, EnumerationMember);
>         success = result.add(WTFMove(*member));
>         if (!success)
>             return fail("Cannot add enumeration member"_str);
>     }
> 
>-    auto rightCurlyBracket = consumeType(Lexer::Token::Type::RightCurlyBracket);
>-    if (!rightCurlyBracket)
>-        return Unexpected<Error>(rightCurlyBracket.error());
>+    CONSUME_TYPE(rightCurlyBracket, RightCurlyBracket);
> 
>     return WTFMove(result);
> }
> 
> auto Parser::parseEnumerationMember() -> Expected<AST::EnumerationMember, Error>
> {
>-    auto identifier = consumeType(Lexer::Token::Type::Identifier);
>-    if (!identifier)
>-        return Unexpected<Error>(identifier.error());
>+    CONSUME_TYPE(identifier, Identifier);
>     auto name = identifier->stringView.toString();
> 
>     if (tryType(Lexer::Token::Type::EqualsSign)) {
>-        auto constantExpression = parseConstantExpression();
>-        if (!constantExpression)
>-            return Unexpected<Error>(constantExpression.error());
>+        PARSE(constantExpression, ConstantExpression);
>         return AST::EnumerationMember(Lexer::Token(*identifier), WTFMove(name), WTFMove(*constantExpression));
>     }
>     return AST::EnumerationMember(Lexer::Token(*identifier), WTFMove(name));
>@@ -957,71 +812,44 @@ auto Parser::parseEnumerationMember() -> Expected<AST::EnumerationMember, Error>
> 
> auto Parser::parseNativeTypeDeclaration() -> Expected<AST::NativeTypeDeclaration, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Native);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto parsedTypedef = consumeType(Lexer::Token::Type::Typedef);
>-    if (!parsedTypedef)
>-        return Unexpected<Error>(parsedTypedef.error());
>-
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-
>-    auto typeArguments = parseTypeArguments();
>-    if (!typeArguments)
>-        return Unexpected<Error>(typeArguments.error());
>-
>-    auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-    if (!semicolon)
>-        return Unexpected<Error>(semicolon.error());
>+    CONSUME_TYPE(origin, Native);
>+    CONSUME_TYPE(parsedTypedef, Typedef);
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(typeArguments, TypeArguments);
>+    CONSUME_TYPE(semicolon, Semicolon);
> 
>     return AST::NativeTypeDeclaration(WTFMove(*origin), name->stringView.toString(), WTFMove(*typeArguments));
> }
> 
> auto Parser::parseNumThreadsFunctionAttribute() -> Expected<AST::NumThreadsFunctionAttribute, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::NumThreads);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>+    CONSUME_TYPE(origin, NumThreads);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
> 
>     auto width = consumeNonNegativeIntegralLiteral();
>     if (!width)
>         return Unexpected<Error>(width.error());
> 
>-    auto comma = consumeType(Lexer::Token::Type::Comma);
>-    if (!comma)
>-        return Unexpected<Error>(comma.error());
>+    CONSUME_TYPE(comma, Comma);
> 
>     auto height = consumeNonNegativeIntegralLiteral();
>     if (!height)
>         return Unexpected<Error>(height.error());
> 
>-    comma = consumeType(Lexer::Token::Type::Comma);
>-    if (!comma)
>-        return Unexpected<Error>(comma.error());
>+    CONSUME_TYPE(secondComma, Comma);
> 
>     auto depth = consumeNonNegativeIntegralLiteral();
>     if (!depth)
>         return Unexpected<Error>(depth.error());
> 
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>     return AST::NumThreadsFunctionAttribute(WTFMove(*origin), *width, *height, *depth);
> }
> 
> auto Parser::parseAttributeBlock() -> Expected<AST::AttributeBlock, Error>
> {
>-    auto leftSquareBracket = consumeType(Lexer::Token::Type::LeftSquareBracket);
>-    if (!leftSquareBracket)
>-        return Unexpected<Error>(leftSquareBracket.error());
>+    CONSUME_TYPE(leftSquareBracket, LeftSquareBracket);
> 
>     AST::AttributeBlock result;
> 
>@@ -1037,295 +865,169 @@ auto Parser::parseAttributeBlock() -> Expected<AST::AttributeBlock, Error>
>         break;
>     }
> 
>-    auto rightSquareBracket = consumeType(Lexer::Token::Type::RightSquareBracket);
>-    if (!rightSquareBracket)
>-        return Unexpected<Error>(rightSquareBracket.error());
>+    CONSUME_TYPE(rightSquareBracket, RightSquareBracket);
> 
>     return WTFMove(result);
> }
> 
> auto Parser::parseParameter() -> Expected<AST::VariableDeclaration, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>     AST::Qualifiers qualifiers = parseQualifiers();
> 
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>+    PARSE(type, Type);
> 
>     String name;
>     if (auto token = tryType(Lexer::Token::Type::Identifier))
>         name = token->stringView.toString();
> 
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>-        return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), Optional<UniqueRef<AST::UnnamedType>>(WTFMove(*type)), WTFMove(name), WTFMove(*semantic), WTF::nullopt);
>-    }
>+    PARSE(semantic, Semantic);
> 
>-    return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(*type) }, WTFMove(name), WTF::nullopt, WTF::nullopt);
>+    return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(*type) }, WTFMove(name), WTFMove(*semantic), WTF::nullopt);
> }
> 
> auto Parser::parseParameters() -> Expected<AST::VariableDeclarations, Error>
> {
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>     AST::VariableDeclarations parameters;
>+
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
>+
>     if (tryType(Lexer::Token::Type::RightParenthesis))
>         return WTFMove(parameters);
> 
>-    auto firstParameter = parseParameter();
>-    if (!firstParameter)
>-        return Unexpected<Error>(firstParameter.error());
>+    PARSE(firstParameter, Parameter);
>     parameters.append(makeUniqueRef<AST::VariableDeclaration>(WTFMove(*firstParameter)));
> 
>     while (tryType(Lexer::Token::Type::Comma)) {
>-        auto parameter = parseParameter();
>-        if (!parameter)
>-            return Unexpected<Error>(parameter.error());
>+        PARSE(parameter, Parameter);
>         parameters.append(makeUniqueRef<AST::VariableDeclaration>(WTFMove(*parameter)));
>     }
> 
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>     return WTFMove(parameters);
> }
> 
> auto Parser::parseFunctionDefinition() -> Expected<AST::FunctionDefinition, Error>
> {
>-    auto functionDeclaration = parseFunctionDeclaration();
>-    if (!functionDeclaration)
>-        return Unexpected<Error>(functionDeclaration.error());
>-
>-    auto block = parseBlock();
>-    if (!block)
>-        return Unexpected<Error>(block.error());
>-
>+    PARSE(functionDeclaration, FunctionDeclaration);
>+    PARSE(block, Block);
>     return AST::FunctionDefinition(WTFMove(*functionDeclaration), WTFMove(*block));
> }
> 
>-auto Parser::parseEntryPointFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
>+auto Parser::parseComputeFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    AST::AttributeBlock attributeBlock;
>-    AST::EntryPointType entryPointType;
>-
>-    auto parsedAttributeBlock = backtrackingScope<Expected<AST::AttributeBlock, Error>>([&]() {
>-        return parseAttributeBlock();
>-    });
>-    if (parsedAttributeBlock) {
>-        auto compute = consumeType(Lexer::Token::Type::Compute);
>-        if (!compute)
>-            return Unexpected<Error>(compute.error());
>-        attributeBlock = WTFMove(*parsedAttributeBlock);
>-        entryPointType = AST::EntryPointType::Compute;
>-    } else {
>-        auto type = consumeTypes({ Lexer::Token::Type::Vertex, Lexer::Token::Type::Fragment });
>-        if (!type)
>-            return Unexpected<Error>(type.error());
>-
>-        switch (origin->type) {
>-        case Lexer::Token::Type::Vertex:
>-            entryPointType = AST::EntryPointType::Vertex;
>-            break;
>-        default:
>-            ASSERT(origin->type == Lexer::Token::Type::Fragment);
>-            entryPointType = AST::EntryPointType::Fragment;
>-            break;
>-        }
>-    }
>+    PEEK(origin);
> 
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>+    PARSE(attributeBlock, AttributeBlock);
>+    CONSUME_TYPE(compute, Compute);
>+    PARSE(type, Type);
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(parameters, Parameters);
>+    PARSE(semantic, Semantic);
>+    bool isOperator = false;
>+    return AST::FunctionDeclaration(WTFMove(*origin), WTFMove(*attributeBlock), AST::EntryPointType::Compute, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTFMove(*semantic), isOperator);
>+}
> 
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>+auto Parser::parseVertexOrFragmentFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
>+{
>+    auto entryPoint = consumeTypes({ Lexer::Token::Type::Vertex, Lexer::Token::Type::Fragment });
>+    if (!entryPoint)
>+        return Unexpected<Error>(entryPoint.error());
>+    auto entryPointType = (entryPoint->type == Lexer::Token::Type::Vertex) ? AST::EntryPointType::Vertex : AST::EntryPointType::Fragment;
> 
>-    auto parameters = parseParameters();
>-    if (!parameters)
>-        return Unexpected<Error>(parameters.error());
>+    PARSE(type, Type);
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(parameters, Parameters);
>+    PARSE(semantic, Semantic);
> 
>     bool isOperator = false;
>-
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>-        return AST::FunctionDeclaration(WTFMove(*origin), WTFMove(attributeBlock), entryPointType, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTFMove(*semantic), isOperator);
>-    }
>-
>-    return AST::FunctionDeclaration(WTFMove(*origin), WTFMove(attributeBlock), entryPointType, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTF::nullopt, isOperator);
>+    return AST::FunctionDeclaration(WTFMove(*entryPoint), { }, entryPointType, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTFMove(*semantic), isOperator);
> }
> 
> auto Parser::parseRegularFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>+    PARSE(type, Type);
> 
>     auto name = consumeTypes({ Lexer::Token::Type::Identifier, Lexer::Token::Type::OperatorName });
>     if (!name)
>         return Unexpected<Error>(name.error());
>     auto isOperator = name->type == Lexer::Token::Type::OperatorName;
> 
>-    auto parameters = parseParameters();
>-    if (!parameters)
>-        return Unexpected<Error>(parameters.error());
>+    PARSE(parameters, Parameters);
>+    PARSE(semantic, Semantic);
> 
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>-        return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTFMove(*semantic), isOperator);
>-    }
>-
>-    return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTF::nullopt, isOperator);
>+    return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), name->stringView.toString(), WTFMove(*parameters), WTFMove(*semantic), isOperator);
> }
> 
> auto Parser::parseOperatorFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Operator);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>-
>-    auto parameters = parseParameters();
>-    if (!parameters)
>-        return Unexpected<Error>(parameters.error());
>+    CONSUME_TYPE(origin, Operator);
>+    PARSE(type, Type);
>+    PARSE(parameters, Parameters);
>+    PARSE(semantic, Semantic);
> 
>     bool isOperator = true;
>-
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>-        return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), "operator cast"_str, WTFMove(*parameters), WTFMove(*semantic), isOperator);
>-    }
>-
>-    return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), "operator cast"_str, WTFMove(*parameters), WTF::nullopt, isOperator);
>+    return AST::FunctionDeclaration(WTFMove(*origin), { }, WTF::nullopt, WTFMove(*type), "operator cast"_str, WTFMove(*parameters), WTFMove(*semantic), isOperator);
> }
> 
> auto Parser::parseFunctionDeclaration() -> Expected<AST::FunctionDeclaration, Error>
> {
>-    auto entryPointFunctionDeclaration = backtrackingScope<Expected<AST::FunctionDeclaration, Error>>([&]() {
>-        return parseEntryPointFunctionDeclaration();
>-    });
>-    if (entryPointFunctionDeclaration)
>-        return WTFMove(*entryPointFunctionDeclaration);
>-
>-    auto regularFunctionDeclaration = backtrackingScope<Expected<AST::FunctionDeclaration, Error>>([&]() {
>-        return parseRegularFunctionDeclaration();
>-    });
>-    if (regularFunctionDeclaration)
>-        return WTFMove(*regularFunctionDeclaration);
>-
>-    auto operatorFunctionDeclaration = backtrackingScope<Expected<AST::FunctionDeclaration, Error>>([&]() {
>+    PEEK(token);
>+    switch (token->type) {
>+    case Lexer::Token::Type::Operator:
>         return parseOperatorFunctionDeclaration();
>-    });
>-    if (operatorFunctionDeclaration)
>-        return WTFMove(*operatorFunctionDeclaration);
>-
>-    return Unexpected<Error>(operatorFunctionDeclaration.error());
>+    case Lexer::Token::Type::Vertex:
>+    case Lexer::Token::Type::Fragment:
>+        return parseVertexOrFragmentFunctionDeclaration();
>+    case Lexer::Token::Type::LeftSquareBracket:
>+        return parseComputeFunctionDeclaration();
>+    default:
>+        return parseRegularFunctionDeclaration();
>+    }
> }
> 
> auto Parser::parseNativeFunctionDeclaration() -> Expected<AST::NativeFunctionDeclaration, Error>
> {
>-    Optional<Lexer::Token> origin;
>+    CONSUME_TYPE(native, Native);
>+    PARSE(functionDeclaration, FunctionDeclaration);
>+    CONSUME_TYPE(semicolon, Semicolon);
> 
>-    auto native = consumeType(Lexer::Token::Type::Native);
>-    if (!native)
>-        return Unexpected<Error>(native.error());
>-    if (!origin)
>-        origin = *native;
>-
>-    auto functionDeclaration = parseFunctionDeclaration();
>-    if (!functionDeclaration)
>-        return Unexpected<Error>(functionDeclaration.error());
>-
>-    auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-    if (!semicolon)
>-        return Unexpected<Error>(semicolon.error());
>-
>-    return AST::NativeFunctionDeclaration(WTFMove(*functionDeclaration));
>-}
>+    return AST::NativeFunctionDeclaration(WTFMove(*functionDeclaration));
>+}
> 
> auto Parser::parseBlock() -> Expected<AST::Block, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::LeftCurlyBracket);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto result = parseBlockBody(WTFMove(*origin));
>-
>-    auto rightCurlyBracket = consumeType(Lexer::Token::Type::RightCurlyBracket);
>-    if (!rightCurlyBracket)
>-        return Unexpected<Error>(rightCurlyBracket.error());
>-
>-    return WTFMove(result);
>+    CONSUME_TYPE(origin, LeftCurlyBracket);
>+    PARSE(result, BlockBody, WTFMove(*origin));
>+    CONSUME_TYPE(rightCurlyBracket, RightCurlyBracket);
>+    return WTFMove(*result);
> }
> 
>-AST::Block Parser::parseBlockBody(Lexer::Token&& origin)
>+auto Parser::parseBlockBody(Lexer::Token&& origin) -> Expected<AST::Block, Error>
> {
>     AST::Statements statements;
>-    while (true) {
>-        auto statement = backtrackingScope<Expected<UniqueRef<AST::Statement>, Error>>([&]() {
>-            return parseStatement();
>-        });
>-        if (statement)
>-            statements.append(WTFMove(*statement));
>-        else
>-            break;
>+    while (!peekTypes({Lexer::Token::Type::RightCurlyBracket, Lexer::Token::Type::Case, Lexer::Token::Type::Default})) {
>+        PARSE(statement, Statement);
>+        statements.append(WTFMove(*statement));
>     }
>     return AST::Block(WTFMove(origin), WTFMove(statements));
> }
> 
> auto Parser::parseIfStatement() -> Expected<AST::IfStatement, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::If);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>-    auto conditional = parseExpression();
>-    if (!conditional)
>-        return Unexpected<Error>(conditional.error());
>-
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>-
>-    auto body = parseStatement();
>-    if (!body)
>-        return Unexpected<Error>(body.error());
>+    CONSUME_TYPE(origin, If);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
>+    PARSE(conditional, Expression);
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
>+    PARSE(body, Statement);
> 
>     Optional<UniqueRef<AST::Statement>> elseBody;
>     if (tryType(Lexer::Token::Type::Else)) {
>-        auto parsedElseBody = parseStatement();
>-        if (!parsedElseBody)
>-            return Unexpected<Error>(parsedElseBody.error());
>+        PARSE(parsedElseBody, Statement);
>         elseBody = WTFMove(*parsedElseBody);
>     }
> 
>@@ -1337,40 +1039,20 @@ auto Parser::parseIfStatement() -> Expected<AST::IfStatement, Error>
> 
> auto Parser::parseSwitchStatement() -> Expected<AST::SwitchStatement, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Switch);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>-    auto value = parseExpression();
>-    if (!value)
>-        return Unexpected<Error>(value.error());
>-
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>-
>-    auto leftCurlyBracket = consumeType(Lexer::Token::Type::LeftCurlyBracket);
>-    if (!leftCurlyBracket)
>-        return Unexpected<Error>(leftCurlyBracket.error());
>+    CONSUME_TYPE(origin, Switch);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
>+    PARSE(value, Expression);
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
>+    CONSUME_TYPE(leftCurlyBracket, LeftCurlyBracket);
> 
>     Vector<AST::SwitchCase> switchCases;
>-    while (true) {
>-        auto switchCase = backtrackingScope<Expected<AST::SwitchCase, Error>>([&]() {
>-            return parseSwitchCase();
>-        });
>-        if (switchCase)
>-            switchCases.append(WTFMove(*switchCase));
>-        else
>-            break;
>+    PEEK(nextToken);
>+    while (nextToken->type != Lexer::Token::Type::RightCurlyBracket) {
>+        PARSE(switchCase, SwitchCase);
>+        switchCases.append(WTFMove(*switchCase));
>     }
> 
>-    auto rightCurlyBracket = consumeType(Lexer::Token::Type::RightCurlyBracket);
>-    if (!rightCurlyBracket)
>-        return Unexpected<Error>(rightCurlyBracket.error());
>+    m_lexer.consumeToken();
> 
>     return AST::SwitchStatement(WTFMove(*origin), WTFMove(*value), WTFMove(switchCases));
> }
>@@ -1383,186 +1065,112 @@ auto Parser::parseSwitchCase() -> Expected<AST::SwitchCase, Error>
> 
>     switch (origin->type) {
>     case Lexer::Token::Type::Case: {
>-        auto value = parseConstantExpression();
>-        if (!value)
>-            return Unexpected<Error>(value.error());
>-
>-        auto origin = consumeType(Lexer::Token::Type::Colon);
>-        if (!origin)
>-            return Unexpected<Error>(origin.error());
>+        PARSE(value, ConstantExpression);
>+        CONSUME_TYPE(colon, Colon);
> 
>-        auto block = parseBlockBody(Lexer::Token(*origin));
>+        PARSE(block, BlockBody, Lexer::Token(*origin));
> 
>-        return AST::SwitchCase(WTFMove(*origin), WTFMove(*value), WTFMove(block));
>+        return AST::SwitchCase(WTFMove(*origin), WTFMove(*value), WTFMove(*block));
>     }
>     default: {
>         ASSERT(origin->type == Lexer::Token::Type::Default);
>-        auto origin = consumeType(Lexer::Token::Type::Colon);
>-        if (!origin)
>-            return Unexpected<Error>(origin.error());
>+        CONSUME_TYPE(colon, Colon);
> 
>-        auto block = parseBlockBody(Lexer::Token(*origin));
>+        PARSE(block, BlockBody, Lexer::Token(*origin));
> 
>-        return AST::SwitchCase(WTFMove(*origin), WTF::nullopt, WTFMove(block));
>+        return AST::SwitchCase(WTFMove(*origin), WTF::nullopt, WTFMove(*block));
>     }
>     }
> }
> 
> auto Parser::parseForLoop() -> Expected<AST::ForLoop, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::For);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    CONSUME_TYPE(origin, For);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
> 
>     auto parseRemainder = [&](Variant<AST::VariableDeclarationsStatement, UniqueRef<AST::Expression>>&& initialization) -> Expected<AST::ForLoop, Error> {
>-        auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-        if (!semicolon)
>-            return Unexpected<Error>(semicolon.error());
>+        CONSUME_TYPE(semicolon, Semicolon);
> 
>-        auto condition = backtrackingScope<Optional<UniqueRef<AST::Expression>>>([&]() -> Optional<UniqueRef<AST::Expression>> {
>+        Optional<UniqueRef<AST::Expression>> condition = WTF::nullopt;
>+        if (!tryType(Lexer::Token::Type::Semicolon)) {
>             if (auto expression = parseExpression())
>-                return { WTFMove(*expression) };
>-            return WTF::nullopt;
>-        });
>-
>-        semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-        if (!semicolon)
>-            return Unexpected<Error>(semicolon.error());
>+                condition = { WTFMove(*expression) };
>+            else
>+                return Unexpected<Error>(expression.error());
>+            CONSUME_TYPE(secondSemicolon, Semicolon);
>+        }
> 
>-        auto increment = backtrackingScope<Optional<UniqueRef<AST::Expression>>>([&]() -> Optional<UniqueRef<AST::Expression>> {
>+        Optional<UniqueRef<AST::Expression>> increment = WTF::nullopt;
>+        if (!tryType(Lexer::Token::Type::RightParenthesis)) {
>             if (auto expression = parseExpression())
>-                return { WTFMove(*expression) };
>-            return WTF::nullopt;
>-        });
>-
>-        auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-        if (!rightParenthesis)
>-            return Unexpected<Error>(rightParenthesis.error());
>+                increment = { WTFMove(*expression) };
>+            else
>+                return Unexpected<Error>(expression.error());
>+            CONSUME_TYPE(rightParenthesis, RightParenthesis);
>+        }
> 
>-        auto body = parseStatement();
>-        if (!body)
>-            return Unexpected<Error>(body.error());
>+        PARSE(body, Statement);
> 
>         return AST::ForLoop(WTFMove(*origin), WTFMove(initialization), WTFMove(condition), WTFMove(increment), WTFMove(*body));
>     };
> 
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>     auto variableDeclarations = backtrackingScope<Expected<AST::VariableDeclarationsStatement, Error>>([&]() {
>         return parseVariableDeclarations();
>     });
>     if (variableDeclarations)
>         return parseRemainder(WTFMove(*variableDeclarations));
> 
>-    auto effectfulExpression = parseEffectfulExpression();
>-    if (!effectfulExpression)
>-        return Unexpected<Error>(effectfulExpression.error());
>+    PARSE(effectfulExpression, EffectfulExpression);
> 
>     return parseRemainder(WTFMove(*effectfulExpression));
> }
> 
> auto Parser::parseWhileLoop() -> Expected<AST::WhileLoop, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::While);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>-    auto conditional = parseExpression();
>-    if (!conditional)
>-        return Unexpected<Error>(conditional.error());
>-
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>-
>-    auto body = parseStatement();
>-    if (!body)
>-        return Unexpected<Error>(body.error());
>+    CONSUME_TYPE(origin, While);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
>+    PARSE(conditional, Expression);
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
>+    PARSE(body, Statement);
> 
>     return AST::WhileLoop(WTFMove(*origin), WTFMove(*conditional), WTFMove(*body));
> }
> 
> auto Parser::parseDoWhileLoop() -> Expected<AST::DoWhileLoop, Error>
> {
>-    auto origin = consumeType(Lexer::Token::Type::Do);
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto body = parseStatement();
>-    if (!body)
>-        return Unexpected<Error>(body.error());
>-
>-    auto whileKeyword = consumeType(Lexer::Token::Type::While);
>-    if (!whileKeyword)
>-        return Unexpected<Error>(whileKeyword.error());
>-
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>-
>-    auto conditional = parseExpression();
>-    if (!conditional)
>-        return Unexpected<Error>(conditional.error());
>-
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(origin, Do);
>+    PARSE(body, Statement);
>+    CONSUME_TYPE(whileKeyword, While);
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
>+    PARSE(conditional, Expression);
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
>+    CONSUME_TYPE(semicolon, Semicolon);
> 
>     return AST::DoWhileLoop(WTFMove(*origin), WTFMove(*body), WTFMove(*conditional));
> }
> 
> auto Parser::parseVariableDeclaration(UniqueRef<AST::UnnamedType>&& type) -> Expected<AST::VariableDeclaration, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>     auto qualifiers = parseQualifiers();
> 
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>-
>-    if (tryType(Lexer::Token::Type::Colon)) {
>-        auto semantic = parseSemantic();
>-        if (!semantic)
>-            return Unexpected<Error>(semantic.error());
>-
>-        if (tryType(Lexer::Token::Type::EqualsSign)) {
>-            auto initializer = parseExpression();
>-            if (!initializer)
>-                return Unexpected<Error>(initializer.error());
>-            return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTFMove(*semantic), WTFMove(*initializer));
>-        }
>-
>-        return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTFMove(*semantic), WTF::nullopt);
>-    }
>+    CONSUME_TYPE(name, Identifier);
>+    PARSE(semantic, Semantic);
> 
>     if (tryType(Lexer::Token::Type::EqualsSign)) {
>-        auto initializer = parseExpression();
>-        if (!initializer)
>-            return Unexpected<Error>(initializer.error());
>-        return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTF::nullopt, WTFMove(*initializer));
>+        PARSE(initializer, PossibleTernaryConditional);
>+        return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTFMove(*semantic), WTFMove(*initializer));
>     }
> 
>-    return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTF::nullopt, WTF::nullopt);
>+    return AST::VariableDeclaration(WTFMove(*origin), WTFMove(qualifiers), { WTFMove(type) }, name->stringView.toString(), WTFMove(*semantic), WTF::nullopt);
> }
> 
> auto Parser::parseVariableDeclarations() -> Expected<AST::VariableDeclarationsStatement, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>-    auto type = parseType();
>-    if (!type)
>-        return Unexpected<Error>(type.error());
>+    PARSE(type, Type);
> 
>     auto firstVariableDeclaration = parseVariableDeclaration((*type)->clone());
>     if (!firstVariableDeclaration)
>@@ -1583,205 +1191,123 @@ auto Parser::parseVariableDeclarations() -> Expected<AST::VariableDeclarationsSt
> 
> auto Parser::parseStatement() -> Expected<UniqueRef<AST::Statement>, Error>
> {
>-    {
>-        auto block = backtrackingScope<Expected<AST::Block, Error>>([&]() {
>-            return parseBlock();
>-        });
>-        if (block)
>-            return { makeUniqueRef<AST::Block>(WTFMove(*block)) };
>-    }
>-
>-    {
>-        auto ifStatement = backtrackingScope<Expected<AST::IfStatement, Error>>([&]() {
>-            return parseIfStatement();
>-        });
>-        if (ifStatement)
>-            return { makeUniqueRef<AST::IfStatement>(WTFMove(*ifStatement)) };
>-    }
>-
>-    {
>-        auto switchStatement = backtrackingScope<Expected<AST::SwitchStatement, Error>>([&]() {
>-            return parseSwitchStatement();
>-        });
>-        if (switchStatement)
>-            return { makeUniqueRef<AST::SwitchStatement>(WTFMove(*switchStatement)) };
>-    }
>-
>-    {
>-        auto forLoop = backtrackingScope<Expected<AST::ForLoop, Error>>([&]() {
>-            return parseForLoop();
>-        });
>-        if (forLoop)
>-            return { makeUniqueRef<AST::ForLoop>(WTFMove(*forLoop)) };
>-    }
>-
>-    {
>-        auto whileLoop = backtrackingScope<Expected<AST::WhileLoop, Error>>([&]() {
>-            return parseWhileLoop();
>-        });
>-        if (whileLoop)
>-            return { makeUniqueRef<AST::WhileLoop>(WTFMove(*whileLoop)) };
>-    }
>-
>-    {
>-        auto doWhileLoop = backtrackingScope<Expected<AST::DoWhileLoop, Error>>([&]() -> Expected<AST::DoWhileLoop, Error> {
>-            auto result = parseDoWhileLoop();
>-            if (!result)
>-                return Unexpected<Error>(result.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return result;
>-        });
>-        if (doWhileLoop)
>-            return { makeUniqueRef<AST::DoWhileLoop>(WTFMove(*doWhileLoop)) };
>-    }
>-
>-    {
>-        auto breakObject = backtrackingScope<Expected<AST::Break, Error>>([&]() -> Expected<AST::Break, Error> {
>-            auto origin = consumeType(Lexer::Token::Type::Break);
>-            if (!origin)
>-                return Unexpected<Error>(origin.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return AST::Break(WTFMove(*origin));
>-        });
>-        if (breakObject)
>-            return { makeUniqueRef<AST::Break>(WTFMove(*breakObject)) };
>-    }
>-
>-    {
>-        auto continueObject = backtrackingScope<Expected<AST::Continue, Error>>([&]() -> Expected<AST::Continue, Error> {
>-            auto origin = consumeType(Lexer::Token::Type::Continue);
>-            if (!origin)
>-                return Unexpected<Error>(origin.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return AST::Continue(WTFMove(*origin));
>-        });
>-        if (continueObject)
>-            return { makeUniqueRef<AST::Continue>(WTFMove(*continueObject)) };
>+    PEEK(token);
>+    switch (token->type) {
>+    case Lexer::Token::Type::LeftCurlyBracket: {
>+        PARSE(block, Block);
>+        return { makeUniqueRef<AST::Block>(WTFMove(*block)) };
>+    }
>+    case Lexer::Token::Type::If: {
>+        PARSE(ifStatement, IfStatement);
>+        return { makeUniqueRef<AST::IfStatement>(WTFMove(*ifStatement)) };
>+    }
>+    case Lexer::Token::Type::Switch: {
>+        PARSE(switchStatement, SwitchStatement);
>+        return { makeUniqueRef<AST::SwitchStatement>(WTFMove(*switchStatement)) };
>+    }
>+    case Lexer::Token::Type::For: {
>+        PARSE(forLoop, ForLoop);
>+        return { makeUniqueRef<AST::ForLoop>(WTFMove(*forLoop)) };
>+    }
>+    case Lexer::Token::Type::While: {
>+        PARSE(whileLoop, WhileLoop);
>+        return { makeUniqueRef<AST::WhileLoop>(WTFMove(*whileLoop)) };
>+    }
>+    case Lexer::Token::Type::Do: {
>+        PARSE(doWhileLoop, DoWhileLoop);
>+        return { makeUniqueRef<AST::DoWhileLoop>(WTFMove(*doWhileLoop)) };
>+    }
>+    case Lexer::Token::Type::Break: {
>+        auto breakToken = m_lexer.consumeToken();
>+        CONSUME_TYPE(semicolon, Semicolon);
>+        auto breakObject = AST::Break(WTFMove(*breakToken));
>+        return { makeUniqueRef<AST::Break>(WTFMove(breakObject)) };
>+    }
>+    case Lexer::Token::Type::Continue: {
>+        auto continueToken = m_lexer.consumeToken();
>+        CONSUME_TYPE(semicolon, Semicolon);
>+        auto continueObject = AST::Continue(WTFMove(*continueToken));
>+        return { makeUniqueRef<AST::Continue>(WTFMove(continueObject)) };
>+    }
>+    case Lexer::Token::Type::Fallthrough: {
>+        auto fallthroughToken = m_lexer.consumeToken();
>+        CONSUME_TYPE(semicolon, Semicolon);
>+        auto fallthroughObject = AST::Fallthrough(WTFMove(*fallthroughToken));
>+        return { makeUniqueRef<AST::Fallthrough>(WTFMove(fallthroughObject)) };
>+    }
>+    case Lexer::Token::Type::Trap: {
>+        auto trapToken = m_lexer.consumeToken();
>+        CONSUME_TYPE(semicolon, Semicolon);
>+        auto trapObject = AST::Trap(WTFMove(*trapToken));
>+        return { makeUniqueRef<AST::Trap>(WTFMove(trapObject)) };
>+    }
>+    case Lexer::Token::Type::Return: {
>+        auto returnToken = m_lexer.consumeToken();
>+        if (auto semicolon = tryType(Lexer::Token::Type::Semicolon)) {
>+            auto returnObject = AST::Return(WTFMove(*returnToken), WTF::nullopt);
>+            return { makeUniqueRef<AST::Return>(WTFMove(returnObject)) };
>+        }
>+        PARSE(expression, Expression);
>+        CONSUME_TYPE(finalSemicolon, Semicolon);
>+        auto returnObject = AST::Return(WTFMove(*returnToken), { WTFMove(*expression) });
>+        return { makeUniqueRef<AST::Return>(WTFMove(returnObject)) };
>     }
>-
>-    {
>-        auto fallthroughObject = backtrackingScope<Expected<AST::Fallthrough, Error>>([&]() -> Expected<AST::Fallthrough, Error> {
>-            auto origin = consumeType(Lexer::Token::Type::Fallthrough);
>-            if (!origin)
>-                return Unexpected<Error>(origin.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return AST::Fallthrough(WTFMove(*origin));
>-        });
>-        if (fallthroughObject)
>-            return { makeUniqueRef<AST::Fallthrough>(WTFMove(*fallthroughObject)) };
>+    case Lexer::Token::Type::Constant:
>+    case Lexer::Token::Type::Device:
>+    case Lexer::Token::Type::Threadgroup:
>+    case Lexer::Token::Type::Thread: {
>+        PARSE(variableDeclarations, VariableDeclarations);
>+        CONSUME_TYPE(semicolon, Semicolon);
>+        return { makeUniqueRef<AST::VariableDeclarationsStatement>(WTFMove(*variableDeclarations)) };
>     }
>-
>-    {
>-        auto trapObject = backtrackingScope<Expected<AST::Trap, Error>>([&]() -> Expected<AST::Trap, Error> {
>-            auto origin = consumeType(Lexer::Token::Type::Trap);
>-            if (!origin)
>-                return Unexpected<Error>(origin.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return AST::Trap(WTFMove(*origin));
>-        });
>-        if (trapObject)
>-            return { makeUniqueRef<AST::Trap>(WTFMove(*trapObject)) };
>+    case Lexer::Token::Type::Identifier: {
>+        PEEK_FURTHER(nextToken);
>+        switch (nextToken->type) {
>+        case Lexer::Token::Type::Identifier:
>+        case Lexer::Token::Type::LessThanSign:
>+        case Lexer::Token::Type::Star:
>+        case Lexer::Token::Type::Qualifier: {
>+            PARSE(variableDeclarations, VariableDeclarations);
>+            CONSUME_TYPE(semicolon, Semicolon);
>+            return { makeUniqueRef<AST::VariableDeclarationsStatement>(WTFMove(*variableDeclarations)) };
>+        }
>+        default:
>+            break;
>+        }
>+        break;
>     }
>-
>-    {
>-        auto returnObject = backtrackingScope<Expected<AST::Return, Error>>([&]() -> Expected<AST::Return, Error> {
>-            auto origin = consumeType(Lexer::Token::Type::Return);
>-            if (!origin)
>-                return Unexpected<Error>(origin.error());
>-
>-            if (auto semicolon = tryType(Lexer::Token::Type::Semicolon))
>-                return AST::Return(WTFMove(*origin), WTF::nullopt);
>-
>-            auto expression = parseExpression();
>-            if (!expression)
>-                return Unexpected<Error>(expression.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>-            return AST::Return(WTFMove(*origin), { WTFMove(*expression) });
>-        });
>-        if (returnObject)
>-            return { makeUniqueRef<AST::Return>(WTFMove(*returnObject)) };
>+    default:
>+        break;
>     }
> 
>     {
>-        auto variableDeclarations = backtrackingScope<Expected<AST::VariableDeclarationsStatement, Error>>([&]() -> Expected<AST::VariableDeclarationsStatement, Error> {
>-            auto result = parseVariableDeclarations();
>-            if (!result)
>-                return Unexpected<Error>(result.error());
>-
>-            auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-            if (!semicolon)
>-                return Unexpected<Error>(semicolon.error());
>-
>+        auto effectfulExpression = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>+            PARSE(result, EffectfulExpression);
>+            CONSUME_TYPE(semicolon, Semicolon);
>             return result;
>         });
>-        if (variableDeclarations)
>-            return { makeUniqueRef<AST::VariableDeclarationsStatement>(WTFMove(*variableDeclarations)) };
>+        if (effectfulExpression)
>+            return { makeUniqueRef<AST::EffectfulExpressionStatement>(WTFMove(*effectfulExpression)) };
>     }
> 
>-    auto effectfulExpression = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>-        auto result = parseEffectfulExpression();
>-        if (!result)
>-            return Unexpected<Error>(result.error());
>-
>-        auto semicolon = consumeType(Lexer::Token::Type::Semicolon);
>-        if (!semicolon)
>-            return Unexpected<Error>(semicolon.error());
>-
>-        return result;
>-    });
>-    if (effectfulExpression)
>-        return { makeUniqueRef<AST::EffectfulExpressionStatement>(WTFMove(*effectfulExpression)) };
>-
>-    return Unexpected<Error>(effectfulExpression.error());
>+    PARSE(variableDeclarations, VariableDeclarations);
>+    CONSUME_TYPE(semicolon, Semicolon);
>+    return { makeUniqueRef<AST::VariableDeclarationsStatement>(WTFMove(*variableDeclarations)) };
> }
> 
> auto Parser::parseEffectfulExpression() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>     Vector<UniqueRef<AST::Expression>> expressions;
>-
>-    auto first = backtrackingScope<Optional<UniqueRef<AST::Expression>>>([&]() -> Optional<UniqueRef<AST::Expression>> {
>-        auto effectfulExpression = parseEffectfulAssignment();
>-        if (!effectfulExpression)
>-            return WTF::nullopt;
>-        return { WTFMove(*effectfulExpression) };
>-    });
>-    if (!first)
>+    if (origin->type == Lexer::Token::Type::Semicolon)
>         return { makeUniqueRef<AST::CommaExpression>(WTFMove(*origin), WTFMove(expressions)) };
> 
>-    expressions.append(WTFMove(*first));
>+    PARSE(effectfulExpression, EffectfulAssignment);
>+    expressions.append(WTFMove(*effectfulExpression));
> 
>     while (tryType(Lexer::Token::Type::Comma)) {
>-        auto expression = parseEffectfulAssignment();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>+        PARSE(expression, EffectfulAssignment);
>         expressions.append(WTFMove(*expression));
>     }
> 
>@@ -1792,111 +1318,28 @@ auto Parser::parseEffectfulExpression() -> Expected<UniqueRef<AST::Expression>,
> 
> auto Parser::parseEffectfulAssignment() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto assignment = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parseAssignment();
>-    });
>-    if (assignment)
>-        return assignment;
>-
>-    assignment = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parseEffectfulPrefix();
>-    });
>-    if (assignment)
>-        return assignment;
>+    PEEK(origin);
> 
>-    return Unexpected<Error>(assignment.error());
>-}
>+    bool isEffectful = false;
>+    PARSE(expression, PossiblePrefix, &isEffectful);
> 
>-auto Parser::parseEffectfulPrefix() -> Expected<UniqueRef<AST::Expression>, Error>
>-{
>-    auto prefix = consumeTypes({ Lexer::Token::Type::PlusPlus, Lexer::Token::Type::MinusMinus });
>-    if (!prefix)
>-        return parseEffectfulSuffix();
>-
>-    auto previous = parsePossiblePrefix();
>-    if (!previous)
>-        return Unexpected<Error>(previous.error());
>-
>-    switch (prefix->type) {
>-    case Lexer::Token::Type::PlusPlus: {
>-        auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*prefix), WTFMove(*previous));
>-        Vector<UniqueRef<AST::Expression>> callArguments;
>-        callArguments.append(result->oldVariableReference());
>-        result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(*prefix), "operator++"_str, WTFMove(callArguments)));
>-        result->setResultExpression(result->newVariableReference());
>-        return { WTFMove(result) };
>-    }
>-    default: {
>-        ASSERT(prefix->type == Lexer::Token::Type::MinusMinus);
>-        auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*prefix), WTFMove(*previous));
>-        Vector<UniqueRef<AST::Expression>> callArguments;
>-        callArguments.append(result->oldVariableReference());
>-        result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(*prefix), "operator--"_str, WTFMove(callArguments)));
>-        result->setResultExpression(result->newVariableReference());
>-        return { WTFMove(result) };
>-    }
>+    if (!isEffectful || peekTypes({
>+        Lexer::Token::Type::EqualsSign,
>+        Lexer::Token::Type::PlusEquals,
>+        Lexer::Token::Type::MinusEquals,
>+        Lexer::Token::Type::TimesEquals,
>+        Lexer::Token::Type::DivideEquals,
>+        Lexer::Token::Type::ModEquals,
>+        Lexer::Token::Type::XorEquals,
>+        Lexer::Token::Type::AndEquals,
>+        Lexer::Token::Type::OrEquals,
>+        Lexer::Token::Type::RightShiftEquals,
>+        Lexer::Token::Type::LeftShiftEquals
>+    })) {
>+        return completeAssignment(WTFMove(*origin), WTFMove(*expression));
>     }
>-}
>-
>-auto Parser::parseEffectfulSuffix() -> Expected<UniqueRef<AST::Expression>, Error>
>-{
>-    auto effectfulSuffix = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>-        auto previous = parsePossibleSuffix();
>-        if (!previous)
>-            return Unexpected<Error>(previous.error());
>-
>-        auto suffix = consumeTypes({ Lexer::Token::Type::PlusPlus, Lexer::Token::Type::MinusMinus });
>-        if (!suffix)
>-            return Unexpected<Error>(suffix.error());
>-
>-        switch (suffix->type) {
>-        case Lexer::Token::Type::PlusPlus: {
>-            auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*suffix), WTFMove(*previous));
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(result->oldVariableReference());
>-            result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(*suffix), "operator++"_str, WTFMove(callArguments)));
>-            result->setResultExpression(result->oldVariableReference());
>-            return { WTFMove(result) };
>-        }
>-        default: {
>-            ASSERT(suffix->type == Lexer::Token::Type::MinusMinus);
>-            auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*suffix), WTFMove(*previous));
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(result->oldVariableReference());
>-            result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(*suffix), "operator--"_str, WTFMove(callArguments)));
>-            result->setResultExpression(result->oldVariableReference());
>-            return { WTFMove(result) };
>-        }
>-        }
>-    });
>-    if (effectfulSuffix)
>-        return effectfulSuffix;
> 
>-    effectfulSuffix = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parseCallExpression();
>-    });
>-    if (effectfulSuffix)
>-        return effectfulSuffix;
>-
>-    effectfulSuffix = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>-        auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-        if (!leftParenthesis)
>-            return Unexpected<Error>(leftParenthesis.error());
>-
>-        auto expression = parseExpression();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>-
>-        auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-        if (!rightParenthesis)
>-            return Unexpected<Error>(rightParenthesis.error());
>-
>-        return { WTFMove(*expression) };
>-    });
>-    if (effectfulSuffix)
>-        return effectfulSuffix;
>-
>-    return Unexpected<Error>(effectfulSuffix.error());
>+    return expression;
> }
> 
> auto Parser::parseLimitedSuffixOperator(UniqueRef<AST::Expression>&& previous) -> SuffixExpression
>@@ -1979,21 +1422,14 @@ auto Parser::parseSuffixOperator(UniqueRef<AST::Expression>&& previous) -> Suffi
> 
> auto Parser::parseExpression() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto first = parsePossibleTernaryConditional();
>-    if (!first)
>-        return Unexpected<Error>(first.error());
>+    PEEK(origin);
> 
>+    PARSE(first, PossibleTernaryConditional);
>     Vector<UniqueRef<AST::Expression>> expressions;
>     expressions.append(WTFMove(*first));
> 
>     while (tryType(Lexer::Token::Type::Comma)) {
>-        auto expression = parsePossibleTernaryConditional();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>+        PARSE(expression, PossibleTernaryConditional);
>         expressions.append(WTFMove(*expression));
>     }
> 
>@@ -2004,46 +1440,37 @@ auto Parser::parseExpression() -> Expected<UniqueRef<AST::Expression>, Error>
> 
> auto Parser::parseTernaryConditional() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>-
>-    auto predicate = parsePossibleLogicalBinaryOperation();
>-    if (!predicate)
>-        return Unexpected<Error>(predicate.error());
>-
>-    auto questionMark = consumeType(Lexer::Token::Type::QuestionMark);
>-    if (!questionMark)
>-        return Unexpected<Error>(questionMark.error());
>+    PEEK(origin);
> 
>-    auto bodyExpression = parseExpression();
>-    if (!bodyExpression)
>-        return Unexpected<Error>(bodyExpression.error());
>+    PARSE(predicate, PossibleLogicalBinaryOperation);
> 
>-    auto colon = consumeType(Lexer::Token::Type::Colon);
>-    if (!colon)
>-        return Unexpected<Error>(colon.error());
>+    return completeTernaryConditional(WTFMove(*origin), WTFMove(*predicate));
>+}
> 
>-    auto elseExpression = parsePossibleTernaryConditional();
>-    if (!elseExpression)
>-        return Unexpected<Error>(elseExpression.error());
>+auto Parser::completeTernaryConditional(Lexer::Token&& origin, UniqueRef<AST::Expression>&& predicate) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>+    CONSUME_TYPE(questionMark, QuestionMark);
>+    PARSE(bodyExpression, Expression);
>+    CONSUME_TYPE(colon, Colon);
>+    PARSE(elseExpression, PossibleTernaryConditional);
> 
>     Vector<UniqueRef<AST::Expression>> castArguments;
>-    castArguments.append(WTFMove(*predicate));
>-    auto boolCast = makeUniqueRef<AST::CallExpression>(Lexer::Token(*origin), "bool"_str, WTFMove(castArguments));
>-    return { makeUniqueRef<AST::TernaryExpression>(WTFMove(*origin), WTFMove(boolCast), WTFMove(*bodyExpression), WTFMove(*elseExpression)) };
>+    castArguments.append(WTFMove(predicate));
>+    auto boolCast = makeUniqueRef<AST::CallExpression>(Lexer::Token(origin), "bool"_str, WTFMove(castArguments));
>+    return { makeUniqueRef<AST::TernaryExpression>(WTFMove(origin), WTFMove(boolCast), WTFMove(*bodyExpression), WTFMove(*elseExpression)) };
> }
> 
> auto Parser::parseAssignment() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto origin = peek();
>-    if (!origin)
>-        return Unexpected<Error>(origin.error());
>+    PEEK(origin);
> 
>-    auto left = parsePossiblePrefix();
>-    if (!left)
>-        return Unexpected<Error>(left.error());
>+    PARSE(left, PossiblePrefix);
>+
>+    return completeAssignment(WTFMove(*origin), WTFMove(*left));
>+}
> 
>+auto Parser::completeAssignment(Lexer::Token&& origin, UniqueRef<AST::Expression>&& left) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     auto assignmentOperator = consumeTypes({
>         Lexer::Token::Type::EqualsSign,
>         Lexer::Token::Type::PlusEquals,
>@@ -2060,12 +1487,10 @@ auto Parser::parseAssignment() -> Expected<UniqueRef<AST::Expression>, Error>
>     if (!assignmentOperator)
>         return Unexpected<Error>(assignmentOperator.error());
> 
>-    auto right = parsePossibleTernaryConditional();
>-    if (!right)
>-        return Unexpected<Error>(right.error());
>+    PARSE(right, PossibleTernaryConditional);
> 
>     if (assignmentOperator->type == Lexer::Token::Type::EqualsSign)
>-        return { makeUniqueRef<AST::AssignmentExpression>(WTFMove(*origin), WTFMove(*left), WTFMove(*right))};
>+        return { makeUniqueRef<AST::AssignmentExpression>(WTFMove(origin), WTFMove(left), WTFMove(*right))};
> 
>     String name;
>     switch (assignmentOperator->type) {
>@@ -2102,45 +1527,55 @@ auto Parser::parseAssignment() -> Expected<UniqueRef<AST::Expression>, Error>
>         break;
>     }
> 
>-    auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*origin), WTFMove(*left));
>+    auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(origin), WTFMove(left));
>     Vector<UniqueRef<AST::Expression>> callArguments;
>     callArguments.append(result->oldVariableReference());
>     callArguments.append(WTFMove(*right));
>-    result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(*origin), WTFMove(name), WTFMove(callArguments)));
>+    result->setNewValueExpression(makeUniqueRef<AST::CallExpression>(WTFMove(origin), WTFMove(name), WTFMove(callArguments)));
>     result->setResultExpression(result->newVariableReference());
>     return { WTFMove(result) };
> }
> 
> auto Parser::parsePossibleTernaryConditional() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto ternaryExpression = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parseTernaryConditional();
>-    });
>-    if (ternaryExpression)
>-        return ternaryExpression;
>+    PEEK(origin);
> 
>-    auto assignmentExpression = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parseAssignment();
>-    });
>-    if (assignmentExpression)
>-        return assignmentExpression;
>+    PARSE(expression, PossiblePrefix);
> 
>-    auto binaryOperation = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() {
>-        return parsePossibleLogicalBinaryOperation();
>-    });
>-    if (binaryOperation)
>-        return binaryOperation;
>+    if (tryTypes({Lexer::Token::Type::EqualsSign,
>+        Lexer::Token::Type::PlusEquals,
>+        Lexer::Token::Type::MinusEquals,
>+        Lexer::Token::Type::TimesEquals,
>+        Lexer::Token::Type::DivideEquals,
>+        Lexer::Token::Type::ModEquals,
>+        Lexer::Token::Type::XorEquals,
>+        Lexer::Token::Type::AndEquals,
>+        Lexer::Token::Type::OrEquals,
>+        Lexer::Token::Type::RightShiftEquals,
>+        Lexer::Token::Type::LeftShiftEquals})) {
>+        return completeAssignment(WTFMove(*origin), WTFMove(*expression));
>+    }
> 
>-    return Unexpected<Error>(binaryOperation.error());
>+    expression = completePossibleShift(WTFMove(*expression));
>+    expression = completePossibleMultiply(WTFMove(*expression));
>+    expression = completePossibleAdd(WTFMove(*expression));
>+    expression = completePossibleRelationalBinaryOperation(WTFMove(*expression));
>+    expression = completePossibleLogicalBinaryOperation(WTFMove(*expression));
>+
>+    PEEK(nextToken);
>+    if (nextToken->type == Lexer::Token::Type::QuestionMark)
>+        return completeTernaryConditional(WTFMove(*origin), WTFMove(*expression));
>+    return expression;
> }
> 
> auto Parser::parsePossibleLogicalBinaryOperation() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto parsedPrevious = parsePossibleRelationalBinaryOperation();
>-    if (!parsedPrevious)
>-        return Unexpected<Error>(parsedPrevious.error());
>-    UniqueRef<AST::Expression> previous = WTFMove(*parsedPrevious);
>+    PARSE(parsedPrevious, PossibleRelationalBinaryOperation);
>+    return completePossibleLogicalBinaryOperation(WTFMove(*parsedPrevious));
>+}
> 
>+auto Parser::completePossibleLogicalBinaryOperation(UniqueRef<AST::Expression>&& previous) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     while (auto logicalBinaryOperation = tryTypes({
>         Lexer::Token::Type::OrOr,
>         Lexer::Token::Type::AndAnd,
>@@ -2148,9 +1583,7 @@ auto Parser::parsePossibleLogicalBinaryOperation() -> Expected<UniqueRef<AST::Ex
>         Lexer::Token::Type::Xor,
>         Lexer::Token::Type::And
>         })) {
>-        auto next = parsePossibleRelationalBinaryOperation();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossibleRelationalBinaryOperation);
> 
>         switch (logicalBinaryOperation->type) {
>         case Lexer::Token::Type::OrOr:
>@@ -2189,11 +1622,12 @@ auto Parser::parsePossibleLogicalBinaryOperation() -> Expected<UniqueRef<AST::Ex
> 
> auto Parser::parsePossibleRelationalBinaryOperation() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto parsedPrevious = parsePossibleShift();
>-    if (!parsedPrevious)
>-        return Unexpected<Error>(parsedPrevious.error());
>-    UniqueRef<AST::Expression> previous = WTFMove(*parsedPrevious);
>+    PARSE(parsedPrevious, PossibleShift);
>+    return completePossibleRelationalBinaryOperation(WTFMove(*parsedPrevious));
>+}
> 
>+auto Parser::completePossibleRelationalBinaryOperation(UniqueRef<AST::Expression>&& previous) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     while (auto relationalBinaryOperation = tryTypes({
>         Lexer::Token::Type::LessThanSign,
>         Lexer::Token::Type::GreaterThanSign,
>@@ -2202,51 +1636,35 @@ auto Parser::parsePossibleRelationalBinaryOperation() -> Expected<UniqueRef<AST:
>         Lexer::Token::Type::EqualComparison,
>         Lexer::Token::Type::NotEqual
>         })) {
>-        auto next = parsePossibleShift();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossibleShift);
>+
>+        Vector<UniqueRef<AST::Expression>> callArguments;
>+        callArguments.append(WTFMove(previous));
>+        callArguments.append(WTFMove(*next));
> 
>         switch (relationalBinaryOperation->type) {
>         case Lexer::Token::Type::LessThanSign: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*relationalBinaryOperation), "operator<"_str, WTFMove(callArguments));
>             break;
>         }
>         case Lexer::Token::Type::GreaterThanSign: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*relationalBinaryOperation), "operator>"_str, WTFMove(callArguments));
>             break;
>         }
>         case Lexer::Token::Type::LessThanOrEqualTo: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*relationalBinaryOperation), "operator<="_str, WTFMove(callArguments));
>             break;
>         }
>         case Lexer::Token::Type::GreaterThanOrEqualTo: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*relationalBinaryOperation), "operator>="_str, WTFMove(callArguments));
>             break;
>         }
>         case Lexer::Token::Type::EqualComparison: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*relationalBinaryOperation), "operator=="_str, WTFMove(callArguments));
>             break;
>         }
>         default: {
>             ASSERT(relationalBinaryOperation->type == Lexer::Token::Type::NotEqual);
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(Lexer::Token(*relationalBinaryOperation), "operator=="_str, WTFMove(callArguments));
>             previous = makeUniqueRef<AST::LogicalNotExpression>(WTFMove(*relationalBinaryOperation), WTFMove(previous));
>             break;
>@@ -2259,32 +1677,29 @@ auto Parser::parsePossibleRelationalBinaryOperation() -> Expected<UniqueRef<AST:
> 
> auto Parser::parsePossibleShift() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto parsedPrevious = parsePossibleAdd();
>-    if (!parsedPrevious)
>-        return Unexpected<Error>(parsedPrevious.error());
>-    UniqueRef<AST::Expression> previous = WTFMove(*parsedPrevious);
>+    PARSE(parsedPrevious, PossibleAdd);
>+    return completePossibleShift(WTFMove(*parsedPrevious));
>+}
> 
>+auto Parser::completePossibleShift(UniqueRef<AST::Expression>&& previous) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     while (auto shift = tryTypes({
>         Lexer::Token::Type::LeftShift,
>         Lexer::Token::Type::RightShift
>         })) {
>-        auto next = parsePossibleAdd();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossibleAdd);
>+
>+        Vector<UniqueRef<AST::Expression>> callArguments;
>+        callArguments.append(WTFMove(previous));
>+        callArguments.append(WTFMove(*next));
> 
>         switch (shift->type) {
>         case Lexer::Token::Type::LeftShift: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*shift), "operator<<"_str, WTFMove(callArguments));
>             break;
>         }
>         default: {
>             ASSERT(shift->type == Lexer::Token::Type::RightShift);
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*shift), "operator>>"_str, WTFMove(callArguments));
>             break;
>         }
>@@ -2296,32 +1711,29 @@ auto Parser::parsePossibleShift() -> Expected<UniqueRef<AST::Expression>, Error>
> 
> auto Parser::parsePossibleAdd() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto parsedPrevious = parsePossibleMultiply();
>-    if (!parsedPrevious)
>-        return Unexpected<Error>(parsedPrevious.error());
>-    UniqueRef<AST::Expression> previous = WTFMove(*parsedPrevious);
>+    PARSE(parsedPrevious, PossibleMultiply);
>+    return completePossibleAdd(WTFMove(*parsedPrevious));
>+}
> 
>+auto Parser::completePossibleAdd(UniqueRef<AST::Expression>&& previous) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     while (auto add = tryTypes({
>         Lexer::Token::Type::Plus,
>         Lexer::Token::Type::Minus
>         })) {
>-        auto next = parsePossibleMultiply();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossibleMultiply);
>+
>+        Vector<UniqueRef<AST::Expression>> callArguments;
>+        callArguments.append(WTFMove(previous));
>+        callArguments.append(WTFMove(*next));
> 
>         switch (add->type) {
>         case Lexer::Token::Type::Plus: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*add), "operator+"_str, WTFMove(callArguments));
>             break;
>         }
>         default: {
>             ASSERT(add->type == Lexer::Token::Type::Minus);
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*add), "operator-"_str, WTFMove(callArguments));
>             break;
>         }
>@@ -2333,40 +1745,34 @@ auto Parser::parsePossibleAdd() -> Expected<UniqueRef<AST::Expression>, Error>
> 
> auto Parser::parsePossibleMultiply() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto parsedPrevious = parsePossiblePrefix();
>-    if (!parsedPrevious)
>-        return Unexpected<Error>(parsedPrevious.error());
>-    UniqueRef<AST::Expression> previous = WTFMove(*parsedPrevious);
>+    PARSE(parsedPrevious, PossiblePrefix);
>+    return completePossibleMultiply(WTFMove(*parsedPrevious));
>+}
> 
>+auto Parser::completePossibleMultiply(UniqueRef<AST::Expression>&& previous) -> Expected<UniqueRef<AST::Expression>, Error>
>+{
>     while (auto multiply = tryTypes({
>         Lexer::Token::Type::Star,
>         Lexer::Token::Type::Divide,
>         Lexer::Token::Type::Mod
>         })) {
>-        auto next = parsePossiblePrefix();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossiblePrefix);
>+
>+        Vector<UniqueRef<AST::Expression>> callArguments;
>+        callArguments.append(WTFMove(previous));
>+        callArguments.append(WTFMove(*next));
> 
>         switch (multiply->type) {
>         case Lexer::Token::Type::Star: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*multiply), "operator*"_str, WTFMove(callArguments));
>             break;
>         }
>         case Lexer::Token::Type::Divide: {
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*multiply), "operator/"_str, WTFMove(callArguments));
>             break;
>         }
>         default: {
>             ASSERT(multiply->type == Lexer::Token::Type::Mod);
>-            Vector<UniqueRef<AST::Expression>> callArguments;
>-            callArguments.append(WTFMove(previous));
>-            callArguments.append(WTFMove(*next));
>             previous = makeUniqueRef<AST::CallExpression>(WTFMove(*multiply), "operator%"_str, WTFMove(callArguments));
>             break;
>         }
>@@ -2376,7 +1782,7 @@ auto Parser::parsePossibleMultiply() -> Expected<UniqueRef<AST::Expression>, Err
>     return WTFMove(previous);
> }
> 
>-auto Parser::parsePossiblePrefix() -> Expected<UniqueRef<AST::Expression>, Error>
>+auto Parser::parsePossiblePrefix(bool *isEffectful) -> Expected<UniqueRef<AST::Expression>, Error>
> {
>     if (auto prefix = tryTypes({
>         Lexer::Token::Type::PlusPlus,
>@@ -2389,12 +1795,12 @@ auto Parser::parsePossiblePrefix() -> Expected<UniqueRef<AST::Expression>, Error
>         Lexer::Token::Type::At,
>         Lexer::Token::Type::Star
>     })) {
>-        auto next = parsePossiblePrefix();
>-        if (!next)
>-            return Unexpected<Error>(next.error());
>+        PARSE(next, PossiblePrefix);
> 
>         switch (prefix->type) {
>         case Lexer::Token::Type::PlusPlus: {
>+            if (isEffectful)
>+                *isEffectful = true;
>             auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*prefix), WTFMove(*next));
>             Vector<UniqueRef<AST::Expression>> callArguments;
>             callArguments.append(result->oldVariableReference());
>@@ -2403,6 +1809,8 @@ auto Parser::parsePossiblePrefix() -> Expected<UniqueRef<AST::Expression>, Error
>             return { WTFMove(result) };
>         }
>         case Lexer::Token::Type::MinusMinus: {
>+            if (isEffectful)
>+                *isEffectful = true;
>             auto result = AST::ReadModifyWriteExpression::create(Lexer::Token(*prefix), WTFMove(*next));
>             Vector<UniqueRef<AST::Expression>> callArguments;
>             callArguments.append(result->oldVariableReference());
>@@ -2441,79 +1849,70 @@ auto Parser::parsePossiblePrefix() -> Expected<UniqueRef<AST::Expression>, Error
>         }
>     }
> 
>-    return parsePossibleSuffix();
>+    return parsePossibleSuffix(isEffectful);
> }
> 
>-auto Parser::parsePossibleSuffix() -> Expected<UniqueRef<AST::Expression>, Error>
>+auto Parser::parsePossibleSuffix(bool *isEffectful) -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto suffix = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>-        auto expression = parseCallExpression();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>+    PEEK(token);
>+    PEEK_FURTHER(nextToken);
> 
>+    if (token->type == Lexer::Token::Type::Identifier && nextToken->type == Lexer::Token::Type::LeftParenthesis) {
>+        PARSE(expression, CallExpression);
>+        if (isEffectful)
>+            *isEffectful = true;
>         while (true) {
>-            auto result = backtrackingScope<SuffixExpression>([&]() -> SuffixExpression {
>-                return parseLimitedSuffixOperator(WTFMove(*expression));
>-            });
>-            expression = WTFMove(result.result);
>-            if (!result)
>+            PEEK(suffixToken);
>+            if (suffixToken->type != Lexer::Token::Type::FullStop && suffixToken->type != Lexer::Token::Type::Arrow && suffixToken->type != Lexer::Token::Type::LeftSquareBracket)
>                 break;
>+            auto result = parseLimitedSuffixOperator(WTFMove(*expression));
>+            expression = WTFMove(result.result);
>         }
>         return expression;
>-    });
>-    if (suffix)
>-        return suffix;
>+    }
> 
>-    suffix = backtrackingScope<Expected<UniqueRef<AST::Expression>, Error>>([&]() -> Expected<UniqueRef<AST::Expression>, Error> {
>-        auto expression = parseTerm();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>+    if (token->type == Lexer::Token::Type::LeftParenthesis && isEffectful)
>+        *isEffectful = true;
> 
>-        while (true) {
>-            auto result = backtrackingScope<SuffixExpression>([&]() -> SuffixExpression {
>-                return parseSuffixOperator(WTFMove(*expression));
>-            });
>-            expression = WTFMove(result.result);
>-            if (!result)
>-                break;
>+    PARSE(expression, Term);
>+    bool isLastSuffixTokenEffectful = false;
>+    while (true) {
>+        PEEK(suffixToken);
>+        if (suffixToken->type != Lexer::Token::Type::FullStop
>+            && suffixToken->type != Lexer::Token::Type::Arrow
>+            && suffixToken->type != Lexer::Token::Type::LeftSquareBracket
>+            && suffixToken->type != Lexer::Token::Type::PlusPlus
>+            && suffixToken->type != Lexer::Token::Type::MinusMinus) {
>+            break;
>         }
>-        return expression;
>-    });
>-    if (suffix)
>-        return suffix;
>-
>-    return Unexpected<Error>(suffix.error());
>+        isLastSuffixTokenEffectful = suffixToken->type == Lexer::Token::Type::PlusPlus || suffixToken->type == Lexer::Token::Type::MinusMinus;
>+        auto result = parseSuffixOperator(WTFMove(*expression));
>+        expression = WTFMove(result.result);
>+    }
>+    if (isLastSuffixTokenEffectful && isEffectful)
>+        *isEffectful = true;
>+    return expression;
> }
> 
> auto Parser::parseCallExpression() -> Expected<UniqueRef<AST::Expression>, Error>
> {
>-    auto name = consumeType(Lexer::Token::Type::Identifier);
>-    if (!name)
>-        return Unexpected<Error>(name.error());
>+    CONSUME_TYPE(name, Identifier);
>     auto callName = name->stringView.toString();
> 
>-    auto leftParenthesis = consumeType(Lexer::Token::Type::LeftParenthesis);
>-    if (!leftParenthesis)
>-        return Unexpected<Error>(leftParenthesis.error());
>+    CONSUME_TYPE(leftParenthesis, LeftParenthesis);
> 
>     Vector<UniqueRef<AST::Expression>> arguments;
>     if (tryType(Lexer::Token::Type::RightParenthesis))
>         return { makeUniqueRef<AST::CallExpression>(WTFMove(*name), WTFMove(callName), WTFMove(arguments)) };
> 
>-    auto firstArgument = parsePossibleTernaryConditional();
>-    if (!firstArgument)
>-        return Unexpected<Error>(firstArgument.error());
>+    PARSE(firstArgument, PossibleTernaryConditional);
>     arguments.append(WTFMove(*firstArgument));
>     while (tryType(Lexer::Token::Type::Comma)) {
>-        auto argument = parsePossibleTernaryConditional();
>-        if (!argument)
>-            return Unexpected<Error>(argument.error());
>+        PARSE(argument, PossibleTernaryConditional);
>         arguments.append(WTFMove(*argument));
>     }
> 
>-    auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-    if (!rightParenthesis)
>-        return Unexpected<Error>(rightParenthesis.error());
>+    CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>     return { makeUniqueRef<AST::CallExpression>(WTFMove(*name), WTFMove(callName), WTFMove(arguments)) };
> }
>@@ -2564,13 +1963,8 @@ auto Parser::parseTerm() -> Expected<UniqueRef<AST::Expression>, Error>
>     }
>     default: {
>         ASSERT(type->type == Lexer::Token::Type::LeftParenthesis);
>-        auto expression = parseExpression();
>-        if (!expression)
>-            return Unexpected<Error>(expression.error());
>-
>-        auto rightParenthesis = consumeType(Lexer::Token::Type::RightParenthesis);
>-        if (!rightParenthesis)
>-            return Unexpected<Error>(rightParenthesis.error());
>+        PARSE(expression, Expression);
>+        CONSUME_TYPE(rightParenthesis, RightParenthesis);
> 
>         return { WTFMove(*expression) };
>     }
>diff --git a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.h b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.h
>index 11ef5cd302e..9f591a293d7 100644
>--- a/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.h
>+++ b/Source/WebCore/Modules/webgpu/WHLSL/WHLSLParser.h
>@@ -96,6 +96,7 @@
> #include "WHLSLWhileLoop.h"
> #include <wtf/Expected.h>
> #include <wtf/Optional.h>
>+#include <wtf/PrintStream.h>
> 
> namespace WebCore {
> 
>@@ -115,11 +116,18 @@ public:
>         }
> 
>         String error;
>+
>+        void dump(PrintStream& out) const
>+        {
>+            out.print(error);
>+        }
>     };
> 
>     Optional<Error> parse(Program&, StringView, Mode);
> 
> private:
>+    // FIXME: We should not need this
>+    // https://bugs.webkit.org/show_bug.cgi?id=198357
>     template<typename T> T backtrackingScope(std::function<T()> callback)
>     {
>         auto state = m_lexer.state();
>@@ -136,10 +144,12 @@ private:
>     };
>     Unexpected<Error> fail(const String& message, TryToPeek = TryToPeek::Yes);
>     Expected<Lexer::Token, Error> peek();
>+    Expected<Lexer::Token, Error> peekFurther();
>+    bool peekTypes(const Vector<Lexer::Token::Type>&);
>     Optional<Lexer::Token> tryType(Lexer::Token::Type);
>-    Optional<Lexer::Token> tryTypes(Vector<Lexer::Token::Type>);
>+    Optional<Lexer::Token> tryTypes(const Vector<Lexer::Token::Type>&);
>     Expected<Lexer::Token, Error> consumeType(Lexer::Token::Type);
>-    Expected<Lexer::Token, Error> consumeTypes(Vector<Lexer::Token::Type>);
>+    Expected<Lexer::Token, Error> consumeTypes(const Vector<Lexer::Token::Type>&);
> 
>     Expected<Variant<int, unsigned>, Error> consumeIntegralLiteral();
>     Expected<unsigned, Error> consumeNonNegativeIntegralLiteral();
>@@ -165,7 +175,7 @@ private:
>     Expected<AST::ResourceSemantic, Error> parseResourceSemantic();
>     Expected<AST::SpecializationConstantSemantic, Error> parseSpecializationConstantSemantic();
>     Expected<AST::StageInOutSemantic, Error> parseStageInOutSemantic();
>-    Expected<AST::Semantic, Error> parseSemantic();
>+    Expected<Optional<AST::Semantic>, Error> parseSemantic();
>     AST::Qualifiers parseQualifiers();
>     Expected<AST::StructureElement, Error> parseStructureElement();
>     Expected<AST::StructureDefinition, Error> parseStructureDefinition();
>@@ -176,7 +186,8 @@ private:
>     Expected<AST::AttributeBlock, Error> parseAttributeBlock();
>     Expected<AST::VariableDeclaration, Error> parseParameter();
>     Expected<AST::VariableDeclarations, Error> parseParameters();
>-    Expected<AST::FunctionDeclaration, Error> parseEntryPointFunctionDeclaration();
>+    Expected<AST::FunctionDeclaration, Error> parseComputeFunctionDeclaration();
>+    Expected<AST::FunctionDeclaration, Error> parseVertexOrFragmentFunctionDeclaration();
>     Expected<AST::FunctionDeclaration, Error> parseRegularFunctionDeclaration();
>     Expected<AST::FunctionDeclaration, Error> parseOperatorFunctionDeclaration();
>     Expected<AST::FunctionDeclaration, Error> parseFunctionDeclaration();
>@@ -184,7 +195,7 @@ private:
>     Expected<AST::NativeFunctionDeclaration, Error> parseNativeFunctionDeclaration();
> 
>     Expected<AST::Block, Error> parseBlock();
>-    AST::Block parseBlockBody(Lexer::Token&& origin);
>+    Expected<AST::Block, Error> parseBlockBody(Lexer::Token&& origin);
>     Expected<AST::IfStatement, Error> parseIfStatement();
>     Expected<AST::SwitchStatement, Error> parseSwitchStatement();
>     Expected<AST::SwitchCase, Error> parseSwitchCase();
>@@ -197,8 +208,6 @@ private:
> 
>     Expected<UniqueRef<AST::Expression>, Error> parseEffectfulExpression();
>     Expected<UniqueRef<AST::Expression>, Error> parseEffectfulAssignment();
>-    Expected<UniqueRef<AST::Expression>, Error> parseEffectfulPrefix();
>-    Expected<UniqueRef<AST::Expression>, Error> parseEffectfulSuffix();
>     struct SuffixExpression {
>         SuffixExpression(UniqueRef<AST::Expression>&& result, bool success)
>             : result(WTFMove(result))
>@@ -215,15 +224,22 @@ private:
> 
>     Expected<UniqueRef<AST::Expression>, Error> parseExpression();
>     Expected<UniqueRef<AST::Expression>, Error> parseTernaryConditional();
>+    Expected<UniqueRef<AST::Expression>, Error> completeTernaryConditional(Lexer::Token&& origin, UniqueRef<AST::Expression>&& predicate);
>     Expected<UniqueRef<AST::Expression>, Error> parseAssignment();
>+    Expected<UniqueRef<AST::Expression>, Error> completeAssignment(Lexer::Token&& origin, UniqueRef<AST::Expression>&& left);
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleTernaryConditional();
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleLogicalBinaryOperation();
>+    Expected<UniqueRef<AST::Expression>, Error> completePossibleLogicalBinaryOperation(UniqueRef<AST::Expression>&& previous);
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleRelationalBinaryOperation();
>+    Expected<UniqueRef<AST::Expression>, Error> completePossibleRelationalBinaryOperation(UniqueRef<AST::Expression>&& previous);
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleShift();
>+    Expected<UniqueRef<AST::Expression>, Error> completePossibleShift(UniqueRef<AST::Expression>&& previous);
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleAdd();
>+    Expected<UniqueRef<AST::Expression>, Error> completePossibleAdd(UniqueRef<AST::Expression>&& previous);
>     Expected<UniqueRef<AST::Expression>, Error> parsePossibleMultiply();
>-    Expected<UniqueRef<AST::Expression>, Error> parsePossiblePrefix();
>-    Expected<UniqueRef<AST::Expression>, Error> parsePossibleSuffix();
>+    Expected<UniqueRef<AST::Expression>, Error> completePossibleMultiply(UniqueRef<AST::Expression>&& previous);
>+    Expected<UniqueRef<AST::Expression>, Error> parsePossiblePrefix(bool *isEffectful = nullptr);
>+    Expected<UniqueRef<AST::Expression>, Error> parsePossibleSuffix(bool *isEffectful = nullptr);
>     Expected<UniqueRef<AST::Expression>, Error> parseCallExpression();
>     Expected<UniqueRef<AST::Expression>, Error> parseTerm();
>

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Attachments on bug 192890: 370292 | 370799 | 370805 | 370907 | 370913 | 370971 | 371228 | 371452