fun declaration

ast_string.go

@@ -140,3 +140,16 @@ func (as *AstStringer) visitWhileStmt(w *WhileStmt) {
 func (as *AstStringer) visitBreakStmt(b *BreakStmt) {
 	as.str.WriteString("(break)")
 }
+
+func (as *AstStringer) visitFunStmt(f *FunStmt) {
+	as.str.WriteString(fmt.Sprintf("(fun %s", f.name.lexeme))
+	if len(f.args) != 0 {
+		as.str.WriteString("(")
+		for _, arg := range f.args {
+			as.str.WriteString(arg.lexeme)
+		}
+		as.str.WriteString(")")
+	}
+	as.str.WriteString(")")
+
+}

callable.go

@@ -4,3 +4,20 @@ type Callable struct {
 	arity int
 	call  func(*Interpreter, ...any) any
 }
+
+func newCallable(f *FunStmt) *Callable {
+	return &Callable{
+		arity: len(f.args),
+		call: func(i *Interpreter, args ...any) any {
+			env := newEnvironment(i.globals)
+
+			for idx, arg := range f.args {
+				env.set(arg.lexeme, args[idx])
+			}
+
+			i.executeBlock(f.body, env)
+
+			return nil
+		},
+	}
+}

interpreter.go

@@ -197,6 +197,10 @@ func (i *Interpreter) visitCall(c *Call) any {
 	return callable.call(i, args...)
 }
 
+func (i *Interpreter) visitFunStmt(f *FunStmt) {
+	i.env.set(f.name.lexeme, newCallable(f))
+}
+
 func (i *Interpreter) visitPrintStmt(p *PrintStmt) {
 	fmt.Printf("%v\n", i.evaluate(p.val))
 }
@@ -217,9 +221,13 @@ func (i *Interpreter) visitVarStmt(v *VarStmt) {
 }
 
 func (i *Interpreter) visitBlockStmt(b *BlockStmt) {
+	i.executeBlock(b, newEnvironment(i.env))
+}
+
+func (i *Interpreter) executeBlock(b *BlockStmt, current *Environment) {
 
 	parentEnv := i.env
-	i.env = newEnvironment(parentEnv)
+	i.env = current
 
 	for _, stmt := range b.stmts {
 

parser.go

@@ -43,18 +43,23 @@ func (p *Parser) parse() ([]Stmt, []error) {
 	return stmts, p.errors
 }
 
-// declaration -> varDecl | statement
+// declaration -> varDecl | funDecl | statement
 func (p *Parser) declaration() Stmt {
 	defer p.synchronize()
 	if p.match(VAR) {
 		return p.varDecl()
 	}
+
+	if p.match(FUN) {
+		return p.function("function")
+	}
+
 	return p.statement()
 }
 
 // varDecl -> "var" IDENTIFIER ("=" expression)? ";"
 func (p *Parser) varDecl() Stmt {
-	name := p.consume(IDENTIFIER, "expect identifier for variable")
+	name := p.consume(IDENTIFIER, "Expect identifier for variable")
 
 	var initializer Expr = nil
 	if p.match(EQUAL) {
@@ -66,6 +71,37 @@ func (p *Parser) varDecl() Stmt {
 	return &VarStmt{name, initializer}
 }
 
+// funDecl -> "fun" function
+// function -> IDENTIFIER "("  parameters? ")" blockStmt
+// parameters -> IDENTIFIER ( "," IDENTIFIER )*
+func (p *Parser) function(kind string) Stmt {
+	name := p.consume(IDENTIFIER, fmt.Sprintf("Expect %s name.", kind))
+
+	p.consume(LEFT_PAREN, fmt.Sprintf("Expect '(' after %s name.", kind))
+
+	args := []Token{}
+	for !p.check(RIGHT_PAREN) {
+		args = append(
+			args,
+			p.consume(
+				IDENTIFIER,
+				fmt.Sprintf("Expect %s argument.", kind),
+			),
+		)
+
+		if p.check(COMMA) {
+			p.advance()
+		}
+	}
+
+	p.consume(RIGHT_PAREN, fmt.Sprintf("Expect ')' after %s name.", kind))
+	p.consume(LEFT_BRACE, fmt.Sprintf("Expect '{' after %s arguments.", kind))
+
+	body := p.blockStmt()
+
+	return &FunStmt{name, args, body}
+}
+
 // statement ->  exprStmt
 //
 //	| whileStmt
@@ -132,7 +168,7 @@ func (p *Parser) printStmt() Stmt {
 }
 
 // blockStmt -> "{" statement* "}"
-func (p *Parser) blockStmt() Stmt {
+func (p *Parser) blockStmt() *BlockStmt {
 
 	stmts := []Stmt{}
 	for !p.check(RIGHT_BRACE) && !p.isAtEnd() {

stmt.go

@@ -3,10 +3,11 @@ package main
 type StmtVisitor interface {
 	visitIfStmt(i *IfStmt)
 	visitVarStmt(v *VarStmt)
+	visitEnvStmt(e *EnvStmt)
+	visitFunStmt(f *FunStmt)
 	visitExprStmt(es *ExprStmt)
 	visitPrintStmt(p *PrintStmt)
 	visitBlockStmt(b *BlockStmt)
-	visitEnvStmt(e *EnvStmt)
 	visitWhileStmt(w *WhileStmt)
 	visitBreakStmt(b *BreakStmt)
 }
@@ -49,7 +50,14 @@ type WhileStmt struct {
 
 type BreakStmt struct{}
 
+type FunStmt struct {
+	name Token
+	args []Token
+	body *BlockStmt
+}
+
 func (i *IfStmt) stmt()    {}
+func (f *FunStmt) stmt()   {}
 func (e *EnvStmt) stmt()   {}
 func (vs *VarStmt) stmt()  {}
 func (es *ExprStmt) stmt() {}
@@ -89,3 +97,7 @@ func (w *WhileStmt) accept(v StmtVisitor) {
 func (b *BreakStmt) accept(v StmtVisitor) {
 	v.visitBreakStmt(b)
 }
+
+func (f *FunStmt) accept(v StmtVisitor) {
+	v.visitFunStmt(f)
+}

tests/functions.lox

@@ -1,4 +1,26 @@
 
-print "functions test";
+print "native function";
 
 print clock();
+
+fun count(n) {
+    if (n > 1) count(n - 1);
+    print n;
+}
+
+count(10);
+
+fun hi(name, surname) {
+    print "hello, " + name + " " + surname + "!";
+}
+
+hi("John", "Doe");
+
+
+fun re(turn) {
+    print "before retrun";
+    return turn;
+    print "should not be printed";
+}
+
+print re("print");