Generate hello world Zig code

Makefile

@@ -1,2 +1,5 @@
 run:
 	go run internal/main.go -o hello.zig programs/hello.go && zig run hello.zig
+
+test:
+	go test ./internal/zig

internal/zig/README.md

@@ -0,0 +1 @@
+A Zig code generator based on the [Zig language specification](https://github.com/ziglang/zig-spec) PEG grammar. The grammar is included in the source so that it can easily be diffed for changes in the future.

internal/zig/ast.go

@@ -1,50 +1,500 @@
+// Abstract Syntax Tree (AST) definitions for Zig, closely following the grammar in zig-grammar.peg
 package zig
 
-// https://github.com/ziglang/zig-spec/blob/master/grammar/grammar.peg
+// Root is the top-level node of a Zig source file.
-
 type Root struct {
-	ContainerDocComment string // //! Doc Comment
+	ContainerDocComment DocComment // //! Doc Comment (optional)
 	ContainerMembers    []*ContainerMember
 }
 
 type ContainerMember struct {
-	// FIXME
+	DocComment DocComment // /// Doc Comment (optional)
-	Decls []Decl
+	Comptime   bool       // 'comptime' field (optional)
+	Field      *ContainerField
+	Decl       Decl // Can be nil if this is a field
 }
 
-type Decl interface{}
+// ContainerField represents a field in a struct/enum/union container.
+type ContainerField struct {
+	Name      string // May be empty for anonymous fields
+	Type      TypeExpr
+	ByteAlign *Expr // Optional
+	Value     Expr  // Optional initializer
+}
 
+// Decl is any top-level declaration (function, variable, usingnamespace, etc).
+type Decl interface {
+	isDecl()
+}
+
+// FnDecl represents a function declaration.
 type FnDecl struct {
-	Name       string
+	Export      bool
+	Extern      bool
+	ExternName  string // Optional string for extern
+	Inline      bool
+	NoInline    bool
+	ThreadLocal bool
+	Name        string // May be empty (anonymous)
 	Params      []*ParamDecl
-	CallConv   string
+	ByteAlign   *Expr
+	AddrSpace   *Expr
+	LinkSection *Expr
+	CallConv    *Expr
 	ReturnType  TypeExpr
 	Body        *Block // nil means semicolon
 }
 
-type ParamDecl struct {
+func (*FnDecl) isDecl() {}
-	DocComment string   // ??? It's what it says
+
-	Name       string   // Can be empty
+// GlobalVarDecl represents a global variable declaration.
-	Type       TypeExpr // anytype when empty
+type GlobalVarDecl struct {
+	Export      bool
+	Extern      bool
+	ExternName  string // Optional string for extern
+	ThreadLocal bool
+	Const       bool
+	Name        string
+	Type        TypeExpr // Optional
+	ByteAlign   *Expr
+	AddrSpace   *Expr
+	LinkSection *Expr
+	Value       Expr // Optional initializer
 }
 
+func (*GlobalVarDecl) isDecl() {}
+
+// UsingNamespaceDecl represents a 'usingnamespace' declaration.
+type UsingNamespaceDecl struct {
+	Expr Expr
+}
+
+func (*UsingNamespaceDecl) isDecl() {}
+
+// ComptimeDecl represents a 'comptime' block at the container level.
+type ComptimeDecl struct {
+	Block *Block
+}
+
+func (*ComptimeDecl) isDecl() {}
+
+// TestDecl represents a 'test' declaration.
+type TestDecl struct {
+	Name  string // Optional
+	Block *Block
+}
+
+func (*TestDecl) isDecl() {}
+
+// ParamDecl represents a function parameter.
+type ParamDecl struct {
+	DocComment DocComment // /// Doc Comment (optional)
+	NoAlias    bool
+	Comptime   bool
+	Name       string   // May be empty
+	Type       TypeExpr // 'anytype' if empty
+}
+
+// Block represents a block of statements.
 type Block struct {
-	Label string
+	Label string // Optional
 	Stmts []Stmt
 }
 
-type Stmt interface{}
+// Stmt is any statement.
+type Stmt interface {
+	isStmt()
+}
 
-type ReturnStmt struct{}
+// ExprStmt represents an expression statement (e.g. a function call as a statement).
+type ExprStmt struct {
+	Expr Expr
+}
 
+func (*ExprStmt) isStmt() {}
+
+// VarDeclStmt represents a variable or const declaration at statement level, supporting destructuring and multi-var declarations.
+type VarDeclStmt struct {
+	Const       bool
+	Pattern     VarPattern // Destructuring or multiple variable names
+	Type        TypeExpr   // Optional
+	Value       Expr       // Optional initializer
+	ByteAlign   Expr       // Optional
+	AddrSpace   Expr       // Optional
+	LinkSection Expr       // Optional
+}
+
+func (*VarDeclStmt) isStmt() {}
+
+// ReturnStmt represents a 'return' statement.
+type ReturnStmt struct {
+	Value Expr // Optional
+}
+
+func (*ReturnStmt) isStmt() {}
+
+// IfStmt represents an if statement (with optional else branch and payload).
+type IfStmt struct {
+	Cond    Expr     // Condition expression
+	Then    Stmt     // Then branch
+	Else    Stmt     // Optional else branch
+	Payload *Payload // Optional payload (for |x|, |*x|, |*x, y|, etc.)
+}
+
+func (*IfStmt) isStmt() {}
+
+// IfExpr represents an if expression (with optional else branch and payload).
+type IfExpr struct {
+	Cond    Expr     // Condition expression
+	Then    Expr     // Then branch
+	Else    Expr     // Optional else branch
+	Payload *Payload // Optional payload (for |x|, |*x|, |*x, y|, etc.)
+}
+
+// DeferStmt represents a 'defer' or 'errdefer' statement.
+type DeferStmt struct {
+	ErrDefer bool     // True for 'errdefer', false for 'defer'
+	Payload  *Payload // Optional payload (for |x|, |*x|, etc.)
+	Stmt     Stmt     // Statement to defer
+}
+
+func (*DeferStmt) isStmt() {}
+
+// SuspendStmt represents a 'suspend' or 'nosuspend' statement.
+type SuspendStmt struct {
+	NoSuspend bool
+	Stmt      Stmt
+}
+
+func (*SuspendStmt) isStmt() {}
+
+// BlockStmt allows a block to be used as a statement.
+type BlockStmt struct {
+	Block *Block
+}
+
+func (*BlockStmt) isStmt() {}
+
+// BreakStmt represents a 'break' statement.
+type BreakStmt struct {
+	Label string // Optional
+	Value Expr   // Optional
+}
+
+func (*BreakStmt) isStmt() {}
+
+// ContinueStmt represents a 'continue' statement.
+type ContinueStmt struct {
+	Label string // Optional
+}
+
+func (*ContinueStmt) isStmt() {}
+
+// LoopStmt represents a for/while loop statement.
+type LoopStmt struct {
+	Inline  bool       // True if 'inline' is present
+	Kind    string     // "for" or "while"
+	Prefix  LoopPrefix // ForPrefix or WhilePrefix
+	Body    Stmt       // Loop body
+	Else    Stmt       // Optional else branch
+	Payload *Payload   // Optional payload (for |x|, |*x|, |*x, y|, etc.)
+}
+
+func (*LoopStmt) isStmt() {}
+
+// LoopPrefix is the prefix of a for/while loop.
+type LoopPrefix interface{}
+
+// ForPrefix represents the prefix of a for loop.
+type ForPrefix struct {
+	Args    []ForArg // For loop arguments
+	Payload *Payload // Payload (|*x, y|, etc.)
+}
+
+// ForArg represents an argument in a for loop.
+type ForArg struct {
+	Expr Expr // Argument expression
+	From Expr // Optional (for .. or ..<)
+}
+
+// WhilePrefix represents the prefix of a while loop.
+type WhilePrefix struct {
+	Cond     Expr     // Condition expression
+	Payload  *Payload // Optional payload (for |x|, |*x|, etc.)
+	Continue Expr     // Optional (while continue expression)
+}
+
+// SwitchStmt represents a switch statement.
+type SwitchStmt struct {
+	Cond   Expr
+	Prongs []*SwitchProng
+}
+
+func (*SwitchStmt) isStmt() {}
+
+// SwitchExpr represents a switch expression.
+type SwitchExpr struct {
+	Cond   Expr
+	Prongs []*SwitchProng
+}
+
+// SwitchProng represents a prong in a switch.
+type SwitchProng struct {
+	Inline  bool          // True if 'inline' is present
+	Cases   []*SwitchCase // List of cases for this prong
+	Payload *Payload      // Optional payload (for |*x, y|, etc.)
+	Expr    Expr          // Result expression for this prong
+}
+
+// SwitchCase represents a case in a switch.
+type SwitchCase struct {
+	Expr   Expr
+	To     Expr // Optional (for ..)
+	IsElse bool
+}
+
+// AsmExpr represents an inline assembly expression.
+type AsmExpr struct {
+	Volatile bool
+	Template Expr
+	Outputs  []*AsmOutputItem
+	Inputs   []*AsmInputItem
+	Clobbers []string
+}
+
+// AsmOutputItem represents an output operand in asm.
+type AsmOutputItem struct {
+	Name       string
+	Constraint string
+	Type       TypeExpr
+}
+
+// AsmInputItem represents an input operand in asm.
+type AsmInputItem struct {
+	Name       string
+	Constraint string
+	Expr       Expr
+}
+
+// ContainerDecl represents a struct, enum, union, or opaque declaration.
+type ContainerDecl struct {
+	Extern     bool
+	Packed     bool
+	Kind       string   // "struct", "enum", "union", "opaque"
+	TagType    TypeExpr // Optional (for enum/union)
+	Fields     []*ContainerMember
+	DocComment DocComment
+}
+
+// ErrorSetDecl represents an error set declaration.
+type ErrorSetDecl struct {
+	Names []string
+}
+
+// InitListExpr represents an initializer list.
+// Exactly one of Fields, Values, or Empty must be set (non-nil/non-empty or true).
+type InitListExpr struct {
+	Fields []*FieldInit // Field initializers (for {.foo = 1, .bar = 2}), mutually exclusive with Values/Empty
+	Values []Expr       // Positional initializers (for {1, 2, 3}), mutually exclusive with Fields/Empty
+	Empty  bool         // True if '{}', mutually exclusive with Fields/Values
+}
+
+// FieldInit represents a field initializer in an init list.
+type FieldInit struct {
+	Name  string
+	Value Expr
+}
+
+// Identifier represents an identifier expression (variable, field, etc).
+type Identifier struct {
+	Name string // The identifier name
+}
+
+// Literal represents a literal value (int, float, string, char).
+type Literal struct {
+	Kind  string // "int", "float", "string", "char"
+	Value string // The literal value as a string
+}
+
+// BinaryExpr represents a binary operation (e.g. +, -, *, /, etc).
+type BinaryExpr struct {
+	Op    string // Operator, e.g. "+", "-", "*", etc.
+	Left  Expr   // Left operand
+	Right Expr   // Right operand
+}
+
+// UnaryExpr represents a unary operation (e.g. !, -, ~, etc).
+type UnaryExpr struct {
+	Op   string // Operator, e.g. "-", "!", "~"
+	Expr Expr   // Operand
+}
+
+// GroupedExpr represents a parenthesized expression.
+type GroupedExpr struct {
+	Expr Expr // The grouped expression
+}
+
+// CallExpr represents a function call.
+type CallExpr struct {
+	Fun  Expr   // Function being called
+	Args []Expr // Arguments to the function
+}
+
+// FieldAccessExpr represents a field/member access as a suffix operation (e.g. foo.bar).
+//
+// Note: in order to call a function on an object, use a CallExpr with a Fun of a FieldAccessExpr.
+// See TestHelloWorld for example.
+type FieldAccessExpr struct {
+	Receiver Expr   // The object being accessed
+	Field    string // The field name
+}
+
+// IndexExpr represents an indexing operation as a suffix (e.g. arr[0]).
+type IndexExpr struct {
+	Receiver Expr // The object being indexed
+	Index    Expr // The index expression
+}
+
+// ResumeExpr represents a 'resume' expression.
+type ResumeExpr struct {
+	Expr Expr // The expression to resume
+}
+
+// ComptimeExpr represents a 'comptime' expression.
+type ComptimeExpr struct {
+	Expr Expr // The expression to evaluate at comptime
+}
+
+// NosuspendExpr represents a 'nosuspend' expression.
+type NosuspendExpr struct {
+	Expr Expr // The expression to evaluate with nosuspend
+}
+
+// ContinueExpr represents a 'continue' expression.
+type ContinueExpr struct {
+	Label string // Optional label
+}
+
+// Expr is any expression.
 type Expr interface{}
 
-// This will need to become a real type expr someday
+// TypeExpr is any type expression.
-type TypeExpr string
+type TypeExpr interface{}
 
-func (t TypeExpr) String() string {
+// DocComment represents a doc comment (/// or //! lines).
-	if string(t) == "" {
+// Newlines in the string automatically add more comments in the output.
-		return "anytype"
+type DocComment string
-	}
+
-	return string(t)
+// Payload represents a control flow payload (|x|, |*x|, |*x, y|, etc).
+// Each entry in Names corresponds to a variable name; the same index in Pointers is true if that name is a pointer (|*x|).
+type Payload struct {
+	Names    []string // Names in the payload, in order
+	Pointers []bool   // True if the corresponding name is a pointer (|*x|, |*x, y|, |*x, *y|, etc.)
+}
+
+// LabeledBlock represents a labeled block or loop (label: {...}).
+type LabeledBlock struct {
+	Label string // The label name
+	Block *Block // The labeled block
+}
+
+// LabeledTypeExpr represents a labeled type block (label: type).
+type LabeledTypeExpr struct {
+	Label string   // The label name
+	Type  TypeExpr // The labeled type
+}
+
+// IfTypeExpr represents an if expression at the type level.
+type IfTypeExpr struct {
+	Cond    Expr
+	Then    TypeExpr
+	Else    TypeExpr // Optional
+	Payload *Payload // Optional
+}
+
+// ForTypeExpr represents a for expression at the type level.
+type ForTypeExpr struct {
+	Prefix  *ForPrefix
+	Body    TypeExpr
+	Else    TypeExpr // Optional
+	Payload *Payload // Optional
+}
+
+// WhileTypeExpr represents a while expression at the type level.
+type WhileTypeExpr struct {
+	Prefix  *WhilePrefix
+	Body    TypeExpr
+	Else    TypeExpr // Optional
+	Payload *Payload // Optional
+}
+
+// DotAsteriskExpr represents a .*
+type DotAsteriskExpr struct {
+	Receiver Expr // The expression being dereferenced
+}
+
+// DotQuestionExpr represents a .?
+type DotQuestionExpr struct {
+	Receiver Expr // The expression being checked for optional
+}
+
+// AsyncExpr represents an 'async' expression.
+type AsyncExpr struct {
+	Expr Expr // The expression to be awaited asynchronously
+}
+
+// TryExpr represents a 'try' expression.
+type TryExpr struct {
+	Expr Expr // The expression to try
+}
+
+// AwaitExpr represents an 'await' expression.
+type AwaitExpr struct {
+	Expr Expr // The expression to await
+}
+
+// UnreachableExpr represents the 'unreachable' keyword.
+type UnreachableExpr struct{}
+
+// EmptyInitListExpr represents an empty initializer list '{}'.
+type EmptyInitListExpr struct{}
+
+// PositionalInitListExpr represents a positional initializer list '{expr, ...}'.
+type PositionalInitListExpr struct {
+	Values []Expr // Expressions in order
+}
+
+// FieldInitListExpr represents a field initializer list '{.field = expr, ...}'.
+type FieldInitListExpr struct {
+	Fields []*FieldInit // Field initializers
+}
+
+// SwitchProngPayload represents a switch prong payload (|*x, y|).
+type SwitchProngPayload struct {
+	Pointer bool
+	Names   []string
+}
+
+// SwitchProngCase represents a single case in a switch prong.
+type SwitchProngCase struct {
+	Expr Expr // The case expression
+	To   Expr // Optional, for ranges
+}
+
+// SwitchProngFull represents a full switch prong with cases and payload.
+type SwitchProngFull struct {
+	Inline  bool
+	Cases   []*SwitchProngCase  // One or more cases
+	Payload *SwitchProngPayload // Optional
+	Expr    Expr                // The result expression
+}
+
+// SwitchElseProng represents an 'else' prong in a switch.
+type SwitchElseProng struct {
+	Expr Expr // The result expression
+}
+
+// VarPattern represents a variable pattern for destructuring or multiple variable declarations.
+type VarPattern struct {
+	Names []string // Variable names (single or multiple for destructuring)
 }

internal/zig/zig-grammar.peg

@@ -0,0 +1,582 @@
+Root <- skip container_doc_comment? ContainerMembers eof
+
+# *** Top level ***
+ContainerMembers <- ContainerDeclarations (ContainerField COMMA)* (ContainerField / ContainerDeclarations)
+
+ContainerDeclarations <- (TestDecl / ComptimeDecl / doc_comment? KEYWORD_pub? Decl)*
+
+TestDecl <- KEYWORD_test (STRINGLITERALSINGLE / IDENTIFIER)? Block
+
+ComptimeDecl <- KEYWORD_comptime Block
+
+Decl
+    <- (KEYWORD_export / KEYWORD_extern STRINGLITERALSINGLE? / KEYWORD_inline / KEYWORD_noinline)? FnProto (SEMICOLON / Block)
+     / (KEYWORD_export / KEYWORD_extern STRINGLITERALSINGLE?)? KEYWORD_threadlocal? GlobalVarDecl
+     / KEYWORD_usingnamespace Expr SEMICOLON
+
+FnProto <- KEYWORD_fn IDENTIFIER? LPAREN ParamDeclList RPAREN ByteAlign? AddrSpace? LinkSection? CallConv? EXCLAMATIONMARK? TypeExpr
+
+VarDeclProto <- (KEYWORD_const / KEYWORD_var) IDENTIFIER (COLON TypeExpr)? ByteAlign? AddrSpace? LinkSection?
+
+GlobalVarDecl <- VarDeclProto (EQUAL Expr)? SEMICOLON
+
+ContainerField <- doc_comment? KEYWORD_comptime? !KEYWORD_fn (IDENTIFIER COLON)? TypeExpr ByteAlign? (EQUAL Expr)?
+
+# *** Block Level ***
+Statement
+    <- KEYWORD_comptime ComptimeStatement
+     / KEYWORD_nosuspend BlockExprStatement
+     / KEYWORD_suspend BlockExprStatement
+     / KEYWORD_defer BlockExprStatement
+     / KEYWORD_errdefer Payload? BlockExprStatement
+     / IfStatement
+     / LabeledStatement
+     / SwitchExpr
+     / VarDeclExprStatement
+
+ComptimeStatement
+    <- BlockExpr
+     / VarDeclExprStatement
+
+IfStatement
+    <- IfPrefix BlockExpr ( KEYWORD_else Payload? Statement )?
+     / IfPrefix AssignExpr ( SEMICOLON / KEYWORD_else Payload? Statement )
+
+LabeledStatement <- BlockLabel? (Block / LoopStatement)
+
+LoopStatement <- KEYWORD_inline? (ForStatement / WhileStatement)
+
+ForStatement
+    <- ForPrefix BlockExpr ( KEYWORD_else Statement )?
+     / ForPrefix AssignExpr ( SEMICOLON / KEYWORD_else Statement )
+
+WhileStatement
+    <- WhilePrefix BlockExpr ( KEYWORD_else Payload? Statement )?
+     / WhilePrefix AssignExpr ( SEMICOLON / KEYWORD_else Payload? Statement )
+
+BlockExprStatement
+    <- BlockExpr
+     / AssignExpr SEMICOLON
+
+BlockExpr <- BlockLabel? Block
+
+# An expression, assignment, or any destructure, as a statement.
+VarDeclExprStatement
+    <- VarDeclProto (COMMA (VarDeclProto / Expr))* EQUAL Expr SEMICOLON
+     / Expr (AssignOp Expr / (COMMA (VarDeclProto / Expr))+ EQUAL Expr)? SEMICOLON
+
+# *** Expression Level ***
+
+# An assignment or a destructure whose LHS are all lvalue expressions.
+AssignExpr <- Expr (AssignOp Expr / (COMMA Expr)+ EQUAL Expr)?
+
+SingleAssignExpr <- Expr (AssignOp Expr)?
+
+Expr <- BoolOrExpr
+
+BoolOrExpr <- BoolAndExpr (KEYWORD_or BoolAndExpr)*
+
+BoolAndExpr <- CompareExpr (KEYWORD_and CompareExpr)*
+
+CompareExpr <- BitwiseExpr (CompareOp BitwiseExpr)?
+
+BitwiseExpr <- BitShiftExpr (BitwiseOp BitShiftExpr)*
+
+BitShiftExpr <- AdditionExpr (BitShiftOp AdditionExpr)*
+
+AdditionExpr <- MultiplyExpr (AdditionOp MultiplyExpr)*
+
+MultiplyExpr <- PrefixExpr (MultiplyOp PrefixExpr)*
+
+PrefixExpr <- PrefixOp* PrimaryExpr
+
+PrimaryExpr
+    <- AsmExpr
+     / IfExpr
+     / KEYWORD_break BreakLabel? Expr?
+     / KEYWORD_comptime Expr
+     / KEYWORD_nosuspend Expr
+     / KEYWORD_continue BreakLabel?
+     / KEYWORD_resume Expr
+     / KEYWORD_return Expr?
+     / BlockLabel? LoopExpr
+     / Block
+     / CurlySuffixExpr
+
+IfExpr <- IfPrefix Expr (KEYWORD_else Payload? Expr)?
+
+Block <- LBRACE Statement* RBRACE
+
+LoopExpr <- KEYWORD_inline? (ForExpr / WhileExpr)
+
+ForExpr <- ForPrefix Expr (KEYWORD_else Expr)?
+
+WhileExpr <- WhilePrefix Expr (KEYWORD_else Payload? Expr)?
+
+CurlySuffixExpr <- TypeExpr InitList?
+
+InitList
+    <- LBRACE FieldInit (COMMA FieldInit)* COMMA? RBRACE
+     / LBRACE Expr (COMMA Expr)* COMMA? RBRACE
+     / LBRACE RBRACE
+
+TypeExpr <- PrefixTypeOp* ErrorUnionExpr
+
+ErrorUnionExpr <- SuffixExpr (EXCLAMATIONMARK TypeExpr)?
+
+SuffixExpr
+    <- KEYWORD_async PrimaryTypeExpr SuffixOp* FnCallArguments
+     / PrimaryTypeExpr (SuffixOp / FnCallArguments)*
+
+PrimaryTypeExpr
+    <- BUILTINIDENTIFIER FnCallArguments
+     / CHAR_LITERAL
+     / ContainerDecl
+     / DOT IDENTIFIER
+     / DOT InitList
+     / ErrorSetDecl
+     / FLOAT
+     / FnProto
+     / GroupedExpr
+     / LabeledTypeExpr
+     / IDENTIFIER
+     / IfTypeExpr
+     / INTEGER
+     / KEYWORD_comptime TypeExpr
+     / KEYWORD_error DOT IDENTIFIER
+     / KEYWORD_anyframe
+     / KEYWORD_unreachable
+     / STRINGLITERAL
+     / SwitchExpr
+
+ContainerDecl <- (KEYWORD_extern / KEYWORD_packed)? ContainerDeclAuto
+
+ErrorSetDecl <- KEYWORD_error LBRACE IdentifierList RBRACE
+
+GroupedExpr <- LPAREN Expr RPAREN
+
+IfTypeExpr <- IfPrefix TypeExpr (KEYWORD_else Payload? TypeExpr)?
+
+LabeledTypeExpr
+    <- BlockLabel Block
+     / BlockLabel? LoopTypeExpr
+
+LoopTypeExpr <- KEYWORD_inline? (ForTypeExpr / WhileTypeExpr)
+
+ForTypeExpr <- ForPrefix TypeExpr (KEYWORD_else TypeExpr)?
+
+WhileTypeExpr <- WhilePrefix TypeExpr (KEYWORD_else Payload? TypeExpr)?
+
+SwitchExpr <- KEYWORD_switch LPAREN Expr RPAREN LBRACE SwitchProngList RBRACE
+
+# *** Assembly ***
+AsmExpr <- KEYWORD_asm KEYWORD_volatile? LPAREN Expr AsmOutput? RPAREN
+
+AsmOutput <- COLON AsmOutputList AsmInput?
+
+AsmOutputItem <- LBRACKET IDENTIFIER RBRACKET STRINGLITERAL LPAREN (MINUSRARROW TypeExpr / IDENTIFIER) RPAREN
+
+AsmInput <- COLON AsmInputList AsmClobbers?
+
+AsmInputItem <- LBRACKET IDENTIFIER RBRACKET STRINGLITERAL LPAREN Expr RPAREN
+
+AsmClobbers <- COLON StringList
+
+# *** Helper grammar ***
+BreakLabel <- COLON IDENTIFIER
+
+BlockLabel <- IDENTIFIER COLON
+
+FieldInit <- DOT IDENTIFIER EQUAL Expr
+
+WhileContinueExpr <- COLON LPAREN AssignExpr RPAREN
+
+LinkSection <- KEYWORD_linksection LPAREN Expr RPAREN
+
+AddrSpace <- KEYWORD_addrspace LPAREN Expr RPAREN
+
+# Fn specific
+CallConv <- KEYWORD_callconv LPAREN Expr RPAREN
+
+ParamDecl
+    <- doc_comment? (KEYWORD_noalias / KEYWORD_comptime)? (IDENTIFIER COLON)? ParamType
+     / DOT3
+
+ParamType
+    <- KEYWORD_anytype
+     / TypeExpr
+
+# Control flow prefixes
+IfPrefix <- KEYWORD_if LPAREN Expr RPAREN PtrPayload?
+
+WhilePrefix <- KEYWORD_while LPAREN Expr RPAREN PtrPayload? WhileContinueExpr?
+
+ForPrefix <- KEYWORD_for LPAREN ForArgumentsList RPAREN PtrListPayload
+
+# Payloads
+Payload <- PIPE IDENTIFIER PIPE
+
+PtrPayload <- PIPE ASTERISK? IDENTIFIER PIPE
+
+PtrIndexPayload <- PIPE ASTERISK? IDENTIFIER (COMMA IDENTIFIER)? PIPE
+
+PtrListPayload <- PIPE ASTERISK? IDENTIFIER (COMMA ASTERISK? IDENTIFIER)* COMMA? PIPE
+
+# Switch specific
+SwitchProng <- KEYWORD_inline? SwitchCase EQUALRARROW PtrIndexPayload? SingleAssignExpr
+
+SwitchCase
+    <- SwitchItem (COMMA SwitchItem)* COMMA?
+     / KEYWORD_else
+
+SwitchItem <- Expr (DOT3 Expr)?
+
+# For specific
+ForArgumentsList <- ForItem (COMMA ForItem)* COMMA?
+
+ForItem <- Expr (DOT2 Expr?)?
+
+# Operators
+AssignOp
+    <- ASTERISKEQUAL
+     / ASTERISKPIPEEQUAL
+     / SLASHEQUAL
+     / PERCENTEQUAL
+     / PLUSEQUAL
+     / PLUSPIPEEQUAL
+     / MINUSEQUAL
+     / MINUSPIPEEQUAL
+     / LARROW2EQUAL
+     / LARROW2PIPEEQUAL
+     / RARROW2EQUAL
+     / AMPERSANDEQUAL
+     / CARETEQUAL
+     / PIPEEQUAL
+     / ASTERISKPERCENTEQUAL
+     / PLUSPERCENTEQUAL
+     / MINUSPERCENTEQUAL
+     / EQUAL
+
+CompareOp
+    <- EQUALEQUAL
+     / EXCLAMATIONMARKEQUAL
+     / LARROW
+     / RARROW
+     / LARROWEQUAL
+     / RARROWEQUAL
+
+BitwiseOp
+    <- AMPERSAND
+     / CARET
+     / PIPE
+     / KEYWORD_orelse
+     / KEYWORD_catch Payload?
+
+BitShiftOp
+    <- LARROW2
+     / RARROW2
+     / LARROW2PIPE
+
+AdditionOp
+    <- PLUS
+     / MINUS
+     / PLUS2
+     / PLUSPERCENT
+     / MINUSPERCENT
+     / PLUSPIPE
+     / MINUSPIPE
+
+MultiplyOp
+    <- PIPE2
+     / ASTERISK
+     / SLASH
+     / PERCENT
+     / ASTERISK2
+     / ASTERISKPERCENT
+     / ASTERISKPIPE
+
+PrefixOp
+    <- EXCLAMATIONMARK
+     / MINUS
+     / TILDE
+     / MINUSPERCENT
+     / AMPERSAND
+     / KEYWORD_try
+     / KEYWORD_await
+
+PrefixTypeOp
+    <- QUESTIONMARK
+     / KEYWORD_anyframe MINUSRARROW
+     / SliceTypeStart (ByteAlign / AddrSpace / KEYWORD_const / KEYWORD_volatile / KEYWORD_allowzero)*
+     / PtrTypeStart (AddrSpace / KEYWORD_align LPAREN Expr (COLON Expr COLON Expr)? RPAREN / KEYWORD_const / KEYWORD_volatile / KEYWORD_allowzero)*
+     / ArrayTypeStart
+
+SuffixOp
+    <- LBRACKET Expr (DOT2 (Expr? (COLON Expr)?)?)? RBRACKET
+     / DOT IDENTIFIER
+     / DOTASTERISK
+     / DOTQUESTIONMARK
+
+FnCallArguments <- LPAREN ExprList RPAREN
+
+# Ptr specific
+SliceTypeStart <- LBRACKET (COLON Expr)? RBRACKET
+
+PtrTypeStart
+    <- ASTERISK
+     / ASTERISK2
+     / LBRACKET ASTERISK (LETTERC / COLON Expr)? RBRACKET
+
+ArrayTypeStart <- LBRACKET Expr (COLON Expr)? RBRACKET
+
+# ContainerDecl specific
+ContainerDeclAuto <- ContainerDeclType LBRACE container_doc_comment? ContainerMembers RBRACE
+
+ContainerDeclType
+    <- KEYWORD_struct (LPAREN Expr RPAREN)?
+     / KEYWORD_opaque
+     / KEYWORD_enum (LPAREN Expr RPAREN)?
+     / KEYWORD_union (LPAREN (KEYWORD_enum (LPAREN Expr RPAREN)? / Expr) RPAREN)?
+
+# Alignment
+ByteAlign <- KEYWORD_align LPAREN Expr RPAREN
+
+# Lists
+IdentifierList <- (doc_comment? IDENTIFIER COMMA)* (doc_comment? IDENTIFIER)?
+
+SwitchProngList <- (SwitchProng COMMA)* SwitchProng?
+
+AsmOutputList <- (AsmOutputItem COMMA)* AsmOutputItem?
+
+AsmInputList <- (AsmInputItem COMMA)* AsmInputItem?
+
+StringList <- (STRINGLITERAL COMMA)* STRINGLITERAL?
+
+ParamDeclList <- (ParamDecl COMMA)* ParamDecl?
+
+ExprList <- (Expr COMMA)* Expr?
+
+# *** Tokens ***
+eof <- !.
+bin <- [01]
+bin_ <- '_'? bin
+oct <- [0-7]
+oct_ <- '_'? oct
+hex <- [0-9a-fA-F]
+hex_ <- '_'? hex
+dec <- [0-9]
+dec_ <- '_'? dec
+
+bin_int <- bin bin_*
+oct_int <- oct oct_*
+dec_int <- dec dec_*
+hex_int <- hex hex_*
+
+ox80_oxBF <- [\200-\277]
+oxF4 <- '\364'
+ox80_ox8F <- [\200-\217]
+oxF1_oxF3 <- [\361-\363]
+oxF0 <- '\360'
+ox90_0xBF <- [\220-\277]
+oxEE_oxEF <- [\356-\357]
+oxED <- '\355'
+ox80_ox9F <- [\200-\237]
+oxE1_oxEC <- [\341-\354]
+oxE0 <- '\340'
+oxA0_oxBF <- [\240-\277]
+oxC2_oxDF <- [\302-\337]
+
+# From https://lemire.me/blog/2018/05/09/how-quickly-can-you-check-that-a-string-is-valid-unicode-utf-8/
+# First Byte      Second Byte     Third Byte      Fourth Byte
+# [0x00,0x7F]
+# [0xC2,0xDF]     [0x80,0xBF]
+#    0xE0         [0xA0,0xBF]     [0x80,0xBF]
+# [0xE1,0xEC]     [0x80,0xBF]     [0x80,0xBF]
+#    0xED         [0x80,0x9F]     [0x80,0xBF]
+# [0xEE,0xEF]     [0x80,0xBF]     [0x80,0xBF]
+#    0xF0         [0x90,0xBF]     [0x80,0xBF]     [0x80,0xBF]
+# [0xF1,0xF3]     [0x80,0xBF]     [0x80,0xBF]     [0x80,0xBF]
+#    0xF4         [0x80,0x8F]     [0x80,0xBF]     [0x80,0xBF]
+
+mb_utf8_literal <-
+       oxF4      ox80_ox8F ox80_oxBF ox80_oxBF
+     / oxF1_oxF3 ox80_oxBF ox80_oxBF ox80_oxBF
+     / oxF0      ox90_0xBF ox80_oxBF ox80_oxBF
+     / oxEE_oxEF ox80_oxBF ox80_oxBF
+     / oxED      ox80_ox9F ox80_oxBF
+     / oxE1_oxEC ox80_oxBF ox80_oxBF
+     / oxE0      oxA0_oxBF ox80_oxBF
+     / oxC2_oxDF ox80_oxBF
+
+# NOTE: `\135` is `]`. We separate to avoid this: [\000-\011\013-\046\050-\133]-\177]
+#                                                 ^                           ^XXXXXX
+ascii_char_not_nl_slash_squote <- [\000-\011\013-\046\050-\133\136-\177] / ']'
+
+char_escape
+    <- "\\x" hex hex
+     / "\\u{" hex+ "}"
+     / "\\" [nr\\t'"]
+char_char
+    <- mb_utf8_literal
+     / char_escape
+     / ascii_char_not_nl_slash_squote
+
+string_char
+    <- char_escape
+     / [^\\"\n]
+
+container_doc_comment <- ('//!' [^\n]* [ \n]* skip)+
+doc_comment <- ('///' [^\n]* [ \n]* skip)+
+line_comment <- '//' ![!/][^\n]* / '////' [^\n]*
+line_string <- ('\\\\' [^\n]* [ \n]*)+
+skip <- ([ \n] / line_comment)*
+
+CHAR_LITERAL <- ['] char_char ['] skip
+FLOAT
+    <- '0x' hex_int '.' hex_int ([pP] [-+]? dec_int)? skip
+     /      dec_int '.' dec_int ([eE] [-+]? dec_int)? skip
+     / '0x' hex_int [pP] [-+]? dec_int skip
+     /      dec_int [eE] [-+]? dec_int skip
+INTEGER
+    <- '0b' bin_int skip
+     / '0o' oct_int skip
+     / '0x' hex_int skip
+     /      dec_int   skip
+STRINGLITERALSINGLE <- ["] string_char* ["] skip
+STRINGLITERAL
+    <- STRINGLITERALSINGLE
+     / (line_string                 skip)+
+IDENTIFIER
+    <- !keyword [A-Za-z_] [A-Za-z0-9_]* skip
+     / '@' STRINGLITERALSINGLE
+BUILTINIDENTIFIER <- '@'[A-Za-z_][A-Za-z0-9_]* skip
+
+
+AMPERSAND            <- '&'      ![=]      skip
+AMPERSANDEQUAL       <- '&='               skip
+ASTERISK             <- '*'      ![*%=|]   skip
+ASTERISK2            <- '**'               skip
+ASTERISKEQUAL        <- '*='               skip
+ASTERISKPERCENT      <- '*%'     ![=]      skip
+ASTERISKPERCENTEQUAL <- '*%='              skip
+ASTERISKPIPE         <- '*|'     ![=]      skip
+ASTERISKPIPEEQUAL    <- '*|='              skip
+CARET                <- '^'      ![=]      skip
+CARETEQUAL           <- '^='               skip
+COLON                <- ':'                skip
+COMMA                <- ','                skip
+DOT                  <- '.'      ![*.?]    skip
+DOT2                 <- '..'     ![.]      skip
+DOT3                 <- '...'              skip
+DOTASTERISK          <- '.*'               skip
+DOTQUESTIONMARK      <- '.?'               skip
+EQUAL                <- '='      ![>=]     skip
+EQUALEQUAL           <- '=='               skip
+EQUALRARROW          <- '=>'               skip
+EXCLAMATIONMARK      <- '!'      ![=]      skip
+EXCLAMATIONMARKEQUAL <- '!='               skip
+LARROW               <- '<'      ![<=]     skip
+LARROW2              <- '<<'     ![=|]     skip
+LARROW2EQUAL         <- '<<='              skip
+LARROW2PIPE          <- '<<|'    ![=]      skip
+LARROW2PIPEEQUAL     <- '<<|='             skip
+LARROWEQUAL          <- '<='               skip
+LBRACE               <- '{'                skip
+LBRACKET             <- '['                skip
+LPAREN               <- '('                skip
+MINUS                <- '-'      ![%=>|]   skip
+MINUSEQUAL           <- '-='               skip
+MINUSPERCENT         <- '-%'     ![=]      skip
+MINUSPERCENTEQUAL    <- '-%='              skip
+MINUSPIPE            <- '-|'     ![=]      skip
+MINUSPIPEEQUAL       <- '-|='              skip
+MINUSRARROW          <- '->'               skip
+PERCENT              <- '%'      ![=]      skip
+PERCENTEQUAL         <- '%='               skip
+PIPE                 <- '|'      ![|=]     skip
+PIPE2                <- '||'               skip
+PIPEEQUAL            <- '|='               skip
+PLUS                 <- '+'      ![%+=|]   skip
+PLUS2                <- '++'               skip
+PLUSEQUAL            <- '+='               skip
+PLUSPERCENT          <- '+%'     ![=]      skip
+PLUSPERCENTEQUAL     <- '+%='              skip
+PLUSPIPE             <- '+|'     ![=]      skip
+PLUSPIPEEQUAL        <- '+|='              skip
+LETTERC              <- 'c'                skip
+QUESTIONMARK         <- '?'                skip
+RARROW               <- '>'      ![>=]     skip
+RARROW2              <- '>>'     ![=]      skip
+RARROW2EQUAL         <- '>>='              skip
+RARROWEQUAL          <- '>='               skip
+RBRACE               <- '}'                skip
+RBRACKET             <- ']'                skip
+RPAREN               <- ')'                skip
+SEMICOLON            <- ';'                skip
+SLASH                <- '/'      ![=]      skip
+SLASHEQUAL           <- '/='               skip
+TILDE                <- '~'                skip
+
+end_of_word <- ![a-zA-Z0-9_] skip
+KEYWORD_addrspace   <- 'addrspace'   end_of_word
+KEYWORD_align       <- 'align'       end_of_word
+KEYWORD_allowzero   <- 'allowzero'   end_of_word
+KEYWORD_and         <- 'and'         end_of_word
+KEYWORD_anyframe    <- 'anyframe'    end_of_word
+KEYWORD_anytype     <- 'anytype'     end_of_word
+KEYWORD_asm         <- 'asm'         end_of_word
+KEYWORD_async       <- 'async'       end_of_word
+KEYWORD_await       <- 'await'       end_of_word
+KEYWORD_break       <- 'break'       end_of_word
+KEYWORD_callconv    <- 'callconv'    end_of_word
+KEYWORD_catch       <- 'catch'       end_of_word
+KEYWORD_comptime    <- 'comptime'    end_of_word
+KEYWORD_const       <- 'const'       end_of_word
+KEYWORD_continue    <- 'continue'    end_of_word
+KEYWORD_defer       <- 'defer'       end_of_word
+KEYWORD_else        <- 'else'        end_of_word
+KEYWORD_enum        <- 'enum'        end_of_word
+KEYWORD_errdefer    <- 'errdefer'    end_of_word
+KEYWORD_error       <- 'error'       end_of_word
+KEYWORD_export      <- 'export'      end_of_word
+KEYWORD_extern      <- 'extern'      end_of_word
+KEYWORD_fn          <- 'fn'          end_of_word
+KEYWORD_for         <- 'for'         end_of_word
+KEYWORD_if          <- 'if'          end_of_word
+KEYWORD_inline      <- 'inline'      end_of_word
+KEYWORD_noalias     <- 'noalias'     end_of_word
+KEYWORD_nosuspend   <- 'nosuspend'   end_of_word
+KEYWORD_noinline    <- 'noinline'    end_of_word
+KEYWORD_opaque      <- 'opaque'      end_of_word
+KEYWORD_or          <- 'or'          end_of_word
+KEYWORD_orelse      <- 'orelse'      end_of_word
+KEYWORD_packed      <- 'packed'      end_of_word
+KEYWORD_pub         <- 'pub'         end_of_word
+KEYWORD_resume      <- 'resume'      end_of_word
+KEYWORD_return      <- 'return'      end_of_word
+KEYWORD_linksection <- 'linksection' end_of_word
+KEYWORD_struct      <- 'struct'      end_of_word
+KEYWORD_suspend     <- 'suspend'     end_of_word
+KEYWORD_switch      <- 'switch'      end_of_word
+KEYWORD_test        <- 'test'        end_of_word
+KEYWORD_threadlocal <- 'threadlocal' end_of_word
+KEYWORD_try         <- 'try'         end_of_word
+KEYWORD_union       <- 'union'       end_of_word
+KEYWORD_unreachable <- 'unreachable' end_of_word
+KEYWORD_usingnamespace <- 'usingnamespace' end_of_word
+KEYWORD_var         <- 'var'         end_of_word
+KEYWORD_volatile    <- 'volatile'    end_of_word
+KEYWORD_while       <- 'while'       end_of_word
+
+keyword <- KEYWORD_addrspace / KEYWORD_align / KEYWORD_allowzero / KEYWORD_and
+         / KEYWORD_anyframe / KEYWORD_anytype / KEYWORD_asm / KEYWORD_async
+         / KEYWORD_await / KEYWORD_break / KEYWORD_callconv / KEYWORD_catch
+         / KEYWORD_comptime / KEYWORD_const / KEYWORD_continue / KEYWORD_defer
+         / KEYWORD_else / KEYWORD_enum / KEYWORD_errdefer / KEYWORD_error / KEYWORD_export
+         / KEYWORD_extern / KEYWORD_fn / KEYWORD_for / KEYWORD_if
+         / KEYWORD_inline / KEYWORD_noalias / KEYWORD_nosuspend / KEYWORD_noinline
+         / KEYWORD_opaque / KEYWORD_or / KEYWORD_orelse / KEYWORD_packed
+         / KEYWORD_pub / KEYWORD_resume / KEYWORD_return / KEYWORD_linksection
+         / KEYWORD_struct / KEYWORD_suspend / KEYWORD_switch / KEYWORD_test
+         / KEYWORD_threadlocal / KEYWORD_try / KEYWORD_union / KEYWORD_unreachable
+         / KEYWORD_usingnamespace / KEYWORD_var / KEYWORD_volatile / KEYWORD_while

internal/zig/zig.go

@@ -7,102 +7,189 @@ import (
 
 type formatter struct {
 	w      io.Writer
+	line   int // 1-based
+	col    int // 1-based, reset to 1 after newline
+	indent int // indentation level
 }
 
-func (f *formatter) WriteString(s string) (n int, err error) {
+// indentStr defines the string used for each indentation level (4 spaces).
-	return f.w.Write([]byte(s))
+const indentStr = "    "
-}
 
-func (f *formatter) Writef(format string, a ...any) (err error) {
+// Writef writes formatted text to the underlying writer and updates line/col counters.
-	_, err = f.w.Write(fmt.Appendf(nil, format, a...))
+// It also handles indentation after newlines when appropriate.
-	return err
+func (f *formatter) Writef(format string, a ...any) {
-}
+	s := fmt.Sprintf(format, a...)
-
+	for i, r := range s {
-func Write(w io.Writer, root *Root) error {
+		if r == '\n' {
-	f := &formatter{
+			f.line++
-		w: w,
+			f.col = 1
+			// After a newline, write indentation for the next line unless it's a closing brace or another newline.
+			if i+1 < len(s) && s[i+1] != '\n' && s[i+1] != '}' {
+				f.writeIndent()
 			}
+		} else {
+			if f.col == 0 {
+				f.col = 1
+			} else {
+				f.col++
+			}
+		}
+	}
+	if _, err := f.w.Write([]byte(s)); err != nil {
+		panic(err)
+	}
+}
+
+// writeIndent writes the current indentation level to the output.
+// Call this at the start of a new line before writing statements or closing braces.
+func (f *formatter) writeIndent() {
+	for i := 0; i < f.indent; i++ {
+		if _, err := f.w.Write([]byte(indentStr)); err != nil {
+			panic(err)
+		}
+		f.col += len(indentStr)
+	}
+}
+
+// Write is the entry point for formatting a Zig AST.
+func Write(w io.Writer, root *Root) (err error) {
+	defer func() {
+		if r := recover(); r != nil {
+			if e, ok := r.(error); ok {
+				err = e
+			} else {
+				panic(r)
+			}
+		}
+	}()
+	f := &formatter{w: w, line: 1, col: 1, indent: 0}
 
 	if root.ContainerDocComment != "" {
-		err := f.Writef("//! %s\n\n", root.ContainerDocComment)
+		f.Writef("//! %s\n\n", root.ContainerDocComment)
-		if err != nil {
-			return err
-		}
 	}
 	for _, member := range root.ContainerMembers {
-		for _, decl := range member.Decls {
+		// Only handle Decl for now (fields not needed for hello world)
-			if err := writeDecl(f, decl); err != nil {
+		if member.Decl != nil {
-				return err
+			writeDecl(f, member.Decl)
-			}
 		}
 	}
 	return nil
 }
 
-func writeDecl(f *formatter, decl Decl) (err error) {
+// writeDecl emits a top-level declaration.
-	switch typ := decl.(type) {
+func writeDecl(f *formatter, decl Decl) {
+	switch d := decl.(type) {
 	case *FnDecl:
-		if err = f.Writef("fn %s(", typ.Name); err != nil {
+		f.Writef("\nfn %s(", d.Name)
-			return err
+		writeParams(f, d.Params)
+		f.Writef(") ")
+		writeTypeExpr(f, d.ReturnType)
+		writeBlock(f, d.Body)
+	case *GlobalVarDecl:
+		if d.Const {
+			f.Writef("const %s = ", d.Name)
+		} else {
+			f.Writef("var %s = ", d.Name)
 		}
-		if err = writeParams(f, typ.Params); err != nil {
+		writeExpr(f, d.Value)
-			return err
+		f.Writef(";\n")
 	}
-		if err = f.Writef(") %s", typ.ReturnType); err != nil {
-			return err
-		}
-		if err = writeBlock(f, typ.Body); err != nil {
-			return err
-		}
-	}
-	return nil
 }
 
-func writeParams(f *formatter, params []*ParamDecl) (err error) {
+// writeParams emits function parameters, separated by commas.
-	for _, param := range params {
+func writeParams(f *formatter, params []*ParamDecl) {
+	for i, param := range params {
+		if i > 0 {
+			f.Writef(", ")
+		}
 		if param.Name != "" {
-			if err = f.Writef("%s: ", param.Name); err != nil {
+			f.Writef("%s: ", param.Name)
-				return err
 		}
+		writeTypeExpr(f, param.Type)
 	}
-		if err = f.Writef("%s", param.Type); err != nil {
-			return err
-		}
-	}
-	return nil
 }
 
-func writeBlock(f *formatter, block *Block) (err error) {
+// writeTypeExpr emits a type expression.
+func writeTypeExpr(f *formatter, typ TypeExpr) {
+	switch t := typ.(type) {
+	case *Identifier:
+		f.Writef("%s", t.Name)
+	case nil:
+		// nothing
+	default:
+		f.Writef("%v", t)
+	}
+}
+
+// writeBlock emits a block, handling indentation for statements and the closing brace.
+func writeBlock(f *formatter, block *Block) {
 	if block == nil {
-		if _, err = f.WriteString(";"); err != nil {
+		f.Writef(";")
-			return err
+		return
 	}
-		return nil
+	f.Writef(" {\n")
-	}
+	f.indent++ // Increase indentation for block contents.
-	if err = f.Writef(" {\n"); err != nil {
+	for i, stmt := range block.Stmts {
-		return err
+		f.writeIndent() // Indent each statement.
-	}
+		writeStmt(f, stmt)
-	for _, stmt := range block.Stmts {
+		if i < len(block.Stmts)-1 {
-		if err = writeStmt(f, stmt); err != nil {
+			f.Writef("\n")
-			return err
-		}
-		// Should this be the job of the formatter?
-		if _, err = f.WriteString("\n"); err != nil {
-			return err
 		}
 	}
-	if err = f.Writef("}\n"); err != nil {
+	f.indent-- // Decrease indentation before closing brace.
-		return err
+	f.Writef("\n")
-	}
+	f.writeIndent() // Indent the closing brace.
-	return nil
+	f.Writef("}\n")
 }
 
-func writeStmt(f *formatter, stmt Stmt) (err error) {
+// writeStmt emits a statement. Indentation is handled by the caller (writeBlock).
-	switch stmt.(type) {
+func writeStmt(f *formatter, stmt Stmt) {
+	switch s := stmt.(type) {
 	case *ReturnStmt:
-		if _, err = f.WriteString("return;"); err != nil {
+		f.Writef("return")
-			return err
+		if s.Value != nil {
+			f.Writef(" ")
+			writeExpr(f, s.Value)
+		}
+		f.Writef(";")
+	case *ExprStmt:
+		writeExpr(f, s.Expr)
+		f.Writef(";")
+	}
+}
+
+// writeExpr emits an expression.
+func writeExpr(f *formatter, expr Expr) {
+	switch e := expr.(type) {
+	case *Identifier:
+		f.Writef("%s", e.Name)
+	case *CallExpr:
+		writeExpr(f, e.Fun)
+		f.Writef("(")
+		for i, arg := range e.Args {
+			if i > 0 {
+				f.Writef(", ")
+			}
+			writeExpr(f, arg)
+		}
+		f.Writef(")")
+	case *FieldAccessExpr:
+		writeExpr(f, e.Receiver)
+		f.Writef(".%s", e.Field)
+	case *Literal:
+		switch e.Kind {
+		case "string":
+			f.Writef("%q", e.Value)
+		default:
+			f.Writef("%v", e.Value)
+		}
+	case *InitListExpr:
+		if e.Empty {
+			f.Writef(".{}")
+		} else {
+			f.Writef(".{")
+			// TODO
+			f.Writef("}")
 		}
 	}
-	return nil
 }

internal/zig/zig_test.go

@@ -19,8 +19,10 @@ func Expect[T cmp.Ordered](expected, actual T) error {
 func TestHelloWorld(t *testing.T) {
 	expected := `//! Hello, world!
 
+const std = @import("std");
+
 fn main() void {
-return;
+    std.debug.print("Hello, world!\n", .{});
 }
 `
 
@@ -28,13 +30,37 @@ return;
 		ContainerDocComment: "Hello, world!",
 		ContainerMembers: []*zig.ContainerMember{
 			{
-				Decls: []zig.Decl{
+				Decl: &zig.GlobalVarDecl{
-					&zig.FnDecl{
+					Const: true,
+					Name:  "std",
+					Value: &zig.CallExpr{
+						Fun: &zig.Identifier{Name: "@import"},
+						Args: []zig.Expr{
+							&zig.Literal{Kind: "string", Value: "std"},
+						},
+					},
+				},
+			},
+			{
+				Decl: &zig.FnDecl{
 					Name:       "main",
-						ReturnType: "void",
+					ReturnType: &zig.Identifier{Name: "void"},
 					Body: &zig.Block{
 						Stmts: []zig.Stmt{
-								&zig.ReturnStmt{},
+							&zig.ExprStmt{
+								Expr: &zig.CallExpr{
+									Fun: &zig.FieldAccessExpr{
+										Receiver: &zig.FieldAccessExpr{
+											Receiver: &zig.Identifier{Name: "std"},
+											Field:    "debug",
+										},
+										Field: "print",
+									},
+									Args: []zig.Expr{
+										&zig.Literal{Kind: "string", Value: "Hello, world!\n"},
+										&zig.InitListExpr{Empty: true},
+									},
+								},
 							},
 						},
 					},