lambda

ast_string.go

@@ -86,6 +86,24 @@ func (as *AstStringer) visitCall(c *Call) any {
 	return nil
 }
 
+func (as *AstStringer) visitLambda(l *Lambda) any {
+	as.str.WriteString("(lambda ")
+	if len(l.args) != 0 {
+		as.str.WriteString("(")
+		for i, arg := range l.args {
+			as.str.WriteString(arg.lexeme)
+			if i < len(l.args)-1 {
+				as.str.WriteString(" ")
+			}
+		}
+		as.str.WriteString(")")
+	}
+	l.body.accept(as)
+	as.str.WriteString(")")
+
+	return nil
+}
+
 func (as *AstStringer) visitPrintStmt(p *PrintStmt) {
 	as.str.WriteString("(print ")
 	p.val.accept(as)
@@ -159,7 +177,6 @@ func (as *AstStringer) visitFunStmt(f *FunStmt) {
 	}
 	f.body.accept(as)
 	as.str.WriteString(")")
-
 }
 
 func (as *AstStringer) visitReturnStmt(r *ReturnStmt) {

callable.go

@@ -6,7 +6,9 @@ type Callable interface {
 }
 
 type Function struct {
-	definition *FunStmt
+	name    Token
+	args    []Token
+	body    *BlockStmt
 	closure *Environment
 }
 
@@ -26,19 +28,19 @@ func (f *Function) call(i *Interpreter, args ...any) (ret any) {
 
 	env := newEnvironment(f.closure)
 
-	for idx, arg := range f.definition.args {
+	for idx, arg := range f.args {
 		env.define(arg.lexeme, args[idx])
 	}
 
-	i.executeBlock(f.definition.body, env)
+	i.executeBlock(f.body, env)
 
 	return nil
 }
 
 func (f *Function) arity() int {
-	return len(f.definition.args)
+	return len(f.args)
 }
 
-func newFunction(fun *FunStmt, env *Environment) Callable {
-	return &Function{fun, env}
+func newFunction(name Token, args []Token, body *BlockStmt, env *Environment) Callable {
+	return &Function{name, args, body, env}
 }

expr.go

@@ -3,6 +3,7 @@ package main
 type ExprVisitor interface {
 	visitCall(c *Call) any
 	visitUnary(u *Unary) any
+	visitLambda(l *Lambda) any
 	visitBinary(b *Binary) any
 	visitLiteral(l *Literal) any
 	visitGrouping(g *Grouping) any
@@ -56,10 +57,17 @@ type Call struct {
 	args   []Expr
 }
 
+type Lambda struct {
+	name Token
+	args []Token
+	body *BlockStmt
+}
+
 func (c *Call) expr()     {}
 func (u *Unary) expr()    {}
 func (a *Assign) expr()   {}
 func (b *Binary) expr()   {}
+func (l *Lambda) expr()   {}
 func (l *Literal) expr()  {}
 func (g *Grouping) expr() {}
 func (v *Variable) expr() {}
@@ -96,3 +104,7 @@ func (l *Logical) accept(v ExprVisitor) any {
 func (c *Call) accept(v ExprVisitor) any {
 	return v.visitCall(c)
 }
+
+func (l *Lambda) accept(v ExprVisitor) any {
+	return v.visitLambda(l)
+}

interpreter.go

@@ -192,7 +192,11 @@ func (i *Interpreter) visitCall(c *Call) any {
 }
 
 func (i *Interpreter) visitFunStmt(f *FunStmt) {
-	i.env.define(f.name.lexeme, newFunction(f, i.env))
+	i.env.define(f.name.lexeme, newFunction(f.name, f.args, f.body, i.env))
+}
+
+func (i *Interpreter) visitLambda(l *Lambda) any {
+	return newFunction(l.name, l.args, l.body, i.env)
 }
 
 func (i *Interpreter) visitReturnStmt(r *ReturnStmt) {

parser.go

@@ -431,7 +431,15 @@ func (p *Parser) arguments(callee Expr) Expr {
 	return &Call{callee, paren, arguments}
 }
 
-// primary -> NUMBER | STRING | "true" | "false" | "nil" | "(" expression ")" | IDENTIFIER
+// primary -> IDENTIFIER
+//
+//	| NUMBER
+//	| STRING
+//	| "true"
+//	| "false"
+//	| "nil"
+//	| "(" expression ")"
+//	| lambda
 func (p *Parser) primary() Expr {
 	switch {
 	case p.match(FALSE):
@@ -442,6 +450,10 @@ func (p *Parser) primary() Expr {
 		return &Literal{nil}
 	}
 
+	if p.match(FUN) {
+		return p.lambda()
+	}
+
 	if p.match(NUMBER, STRING) {
 		return &Literal{p.previous().literal}
 	}
@@ -461,6 +473,34 @@ func (p *Parser) primary() Expr {
 	return nil
 }
 
+func (p *Parser) lambda() Expr {
+	name := p.previous()
+
+	p.consume(LEFT_PAREN, "Expect '(' before lambda arguments.")
+
+	args := []Token{}
+	for !p.check(RIGHT_PAREN) {
+		args = append(
+			args,
+			p.consume(
+				IDENTIFIER,
+				"Expect lambda argument.",
+			),
+		)
+
+		if p.check(COMMA) {
+			p.advance()
+		}
+	}
+
+	p.consume(RIGHT_PAREN, "Expect ')' after lambda arguments.")
+	p.consume(LEFT_BRACE, "Expect '{' before lambda body.")
+
+	body := p.blockStmt()
+
+	return &Lambda{name, args, body}
+}
+
 func (p *Parser) previous() Token {
 	return p.tokens[p.current-1]
 }

tests/functions.lox

@@ -59,3 +59,13 @@ var counter = makeCounter();
 
 counter();
 counter();
+
+fun thrice(fn) {
+    for (var i = 1; i <= 3; i = i + 1) {
+        fn(i);
+    }
+}
+
+thrice(fun (a) { print a; });
+
+print fun () { return "hello, "; }() + "world";