scope and binding

ast_string.go

@@ -74,7 +74,9 @@ func (as *AstStringer) visitLogical(l *Logical) any {
 func (as *AstStringer) visitCall(c *Call) any {
 	as.str.WriteString("(call ")
 	c.callee.accept(as)
+	if len(c.args) != 0 {
 		as.str.WriteString(" ")
+	}
 	for i, arg := range c.args {
 		arg.accept(as)
 		if i < len(c.args)-1 {
@@ -98,7 +100,9 @@ func (as *AstStringer) visitLambda(l *Lambda) any {
 		}
 		as.str.WriteString(")")
 	}
-	l.body.accept(as)
+	for _, stmt := range l.body {
+		stmt.accept(as)
+	}
 	as.str.WriteString(")")
 
 	return nil
@@ -137,7 +141,7 @@ func (as *AstStringer) visitBlockStmt(b *BlockStmt) {
 
 func (as *AstStringer) visitIfStmt(i *IfStmt) {
 	as.str.WriteString("(if ")
-	i.expr.accept(as)
+	i.cond.accept(as)
 	as.str.WriteString(" ")
 	i.then.accept(as)
 	if i.or != nil {
@@ -164,7 +168,7 @@ func (as *AstStringer) visitBreakStmt(b *BreakStmt) {
 }
 
 func (as *AstStringer) visitFunStmt(f *FunStmt) {
-	as.str.WriteString(fmt.Sprintf("(fun %s", f.name.lexeme))
+	as.str.WriteString(fmt.Sprintf("(fun %s ", f.name.lexeme))
 	if len(f.args) != 0 {
 		as.str.WriteString("(")
 		for i, arg := range f.args {
@@ -175,7 +179,9 @@ func (as *AstStringer) visitFunStmt(f *FunStmt) {
 		}
 		as.str.WriteString(")")
 	}
-	f.body.accept(as)
+	for _, stmt := range f.body {
+		stmt.accept(as)
+	}
 	as.str.WriteString(")")
 }
 

callable.go

@@ -8,7 +8,7 @@ type Callable interface {
 type Function struct {
 	name    Token
 	args    []Token
-	body    *BlockStmt
+	body    []Stmt
 	closure *Environment
 }
 
@@ -41,6 +41,6 @@ func (f *Function) arity() int {
 	return len(f.args)
 }
 
-func newFunction(name Token, args []Token, body *BlockStmt, env *Environment) Callable {
+func newFunction(name Token, args []Token, body []Stmt, env *Environment) Callable {
 	return &Function{name, args, body, env}
 }

env.go

@@ -44,3 +44,20 @@ func (env *Environment) assign(key Token, val any) *RuntimeError {
 
 	return env.enclosing.assign(key, val)
 }
+
+func (env *Environment) getAt(distance int, key string) any {
+	return env.ancestor(distance).get(key)
+}
+
+func (env *Environment) assignAt(distance int, key Token, val any) {
+	env.ancestor(distance).values[key.lexeme] = val
+}
+
+func (env *Environment) ancestor(distance int) *Environment {
+	parent := env
+	for i := 0; i < distance; i++ {
+		parent = parent.enclosing
+	}
+
+	return parent
+}

expr.go

@@ -60,7 +60,7 @@ type Call struct {
 type Lambda struct {
 	name Token
 	args []Token
-	body *BlockStmt
+	body []Stmt
 }
 
 func (c *Call) expr()     {}

glox.go

@@ -28,12 +28,22 @@ func (gl *Glox) runPrompt() {
 	scanner := bufio.NewScanner(os.Stdin)
 	scanner.Split(bufio.ScanLines)
 
+	doRun := func(line []byte) {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Println(err)
+			}
+		}()
+
+		gl.run(line)
+	}
+
 	for {
 		print("> ")
 		if !scanner.Scan() {
 			break
 		}
-		gl.run(scanner.Bytes())
+		doRun(scanner.Bytes())
 	}
 }
 
@@ -48,11 +58,29 @@ func (gl *Glox) runFile(path string) {
 }
 
 func (gl *Glox) run(source []byte) {
-	tokens, _ := newScanner(source).scan()
+	tokens, err := newScanner(source).scan()
 
-	stmts, _ := newParser(tokens).parse()
+	if err != nil {
+		panic(err)
+	}
+
+	stmts, parseErrs := newParser(tokens).parse()
+
+	if parseErrs != nil {
+		panic(parseErrs)
+	}
 
 	fmt.Println(AstStringer{stmts: stmts})
 
-	gl.Interpreter.interpret(stmts)
+	resolveErrs := newResolver(gl.Interpreter).resolveStmts(stmts...)
+
+	if resolveErrs != nil {
+		panic(resolveErrs)
+	}
+
+	interpreterErrs := gl.Interpreter.interpret(stmts)
+
+	if interpreterErrs != nil {
+		panic(interpreterErrs)
+	}
 }

interpreter.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"log"
 	"reflect"
@@ -10,6 +11,7 @@ import (
 type Interpreter struct {
 	env     *Environment
 	globals *Environment
+	locals  map[Expr]int
 	errors  []error
 	brk     bool
 }
@@ -36,12 +38,13 @@ func newInterpreter() *Interpreter {
 	return &Interpreter{
 		env:     globals,
 		globals: globals,
+		locals:  map[Expr]int{},
 		errors:  []error{},
 		brk:     false,
 	}
 }
 
-func (i *Interpreter) interpret(stmts []Stmt) []error {
+func (i *Interpreter) interpret(stmts []Stmt) error {
 	defer i.recover()
 
 	i.errors = []error{}
@@ -50,7 +53,7 @@ func (i *Interpreter) interpret(stmts []Stmt) []error {
 		stmt.accept(i)
 	}
 
-	return i.errors
+	return errors.Join(i.errors...)
 }
 
 func (i *Interpreter) recover() {
@@ -135,12 +138,19 @@ func (i *Interpreter) visitUnary(u *Unary) any {
 }
 
 func (i *Interpreter) visitVariable(v *Variable) any {
-	return i.env.get(v.name.lexeme)
+	return i.lookUpVariable(v.name, v)
 }
 
 func (i *Interpreter) visitAssignment(a *Assign) any {
 	val := i.evaluate(a.value)
-	err := i.env.assign(a.variable, val)
+	distance, isLocal := i.locals[a]
+
+	if isLocal {
+		i.env.assignAt(distance, a.variable, val)
+		return val
+	}
+
+	err := i.globals.assign(a.variable, val)
 	if err != nil {
 		i.panic(err)
 	}
@@ -229,10 +239,10 @@ func (i *Interpreter) visitVarStmt(v *VarStmt) {
 }
 
 func (i *Interpreter) visitBlockStmt(b *BlockStmt) {
-	i.executeBlock(b, newEnvironment(i.env))
+	i.executeBlock(b.stmts, newEnvironment(i.env))
 }
 
-func (i *Interpreter) executeBlock(b *BlockStmt, current *Environment) {
+func (i *Interpreter) executeBlock(stmts []Stmt, current *Environment) {
 
 	parentEnv := i.env
 	i.env = current
@@ -243,7 +253,7 @@ func (i *Interpreter) executeBlock(b *BlockStmt, current *Environment) {
 		i.env = parentEnv
 	}()
 
-	for _, stmt := range b.stmts {
+	for _, stmt := range stmts {
 
 		if i.brk {
 			break
@@ -259,7 +269,7 @@ func (i *Interpreter) visitBreakStmt(b *BreakStmt) {
 }
 
 func (i *Interpreter) visitIfStmt(iff *IfStmt) {
-	if isTruthy(i.evaluate(iff.expr)) {
+	if isTruthy(i.evaluate(iff.cond)) {
 		iff.then.accept(i)
 
 	} else if iff.or != nil {
@@ -278,6 +288,8 @@ func (i *Interpreter) visitEnvStmt(e *EnvStmt) {
 		walker = walker.enclosing
 	}
 
+	fmt.Printf("globals: %+v\n", *i.globals)
+
 	for ident, e := range flatten {
 		fmt.Printf("%*s", ident, "")
 		fmt.Printf("%+v\n", *e)
@@ -296,6 +308,20 @@ func (i *Interpreter) visitWhileStmt(w *WhileStmt) {
 	}
 }
 
+func (i *Interpreter) resolve(expr Expr, depth int) {
+	i.locals[expr] = depth
+}
+
+func (i *Interpreter) lookUpVariable(name Token, expr Expr) any {
+	distance, isLocal := i.locals[expr]
+
+	if !isLocal {
+		return i.globals.get(name.lexeme)
+	}
+
+	return i.env.getAt(distance, name.lexeme)
+}
+
 func (i *Interpreter) panic(re *RuntimeError) {
 	i.errors = append(i.errors, re)
 	log.Println(re)

parser.go

@@ -1,8 +1,8 @@
 package main
 
 import (
+	"errors"
 	"fmt"
-	"log"
 )
 
 type Parser struct {
@@ -28,7 +28,7 @@ func newParser(tokens []Token) *Parser {
 }
 
 // program -> declaration* EOF
-func (p *Parser) parse() ([]Stmt, []error) {
+func (p *Parser) parse() ([]Stmt, error) {
 	defer p.recover()
 
 	stmts := []Stmt{}
@@ -40,7 +40,7 @@ func (p *Parser) parse() ([]Stmt, []error) {
 		}
 	}
 
-	return stmts, p.errors
+	return stmts, errors.Join(p.errors...)
 }
 
 // declaration -> varDecl | funDecl | statement
@@ -97,7 +97,7 @@ func (p *Parser) function(kind string) Stmt {
 	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()
+	body := p.block()
 
 	return &FunStmt{name, args, body}
 }
@@ -172,8 +172,7 @@ func (p *Parser) printStmt() Stmt {
 	return &PrintStmt{expr}
 }
 
-// blockStmt -> "{" statement* "}"
+func (p *Parser) block() []Stmt {
-func (p *Parser) blockStmt() *BlockStmt {
 
 	stmts := []Stmt{}
 	for !p.check(RIGHT_BRACE) && !p.isAtEnd() {
@@ -182,7 +181,12 @@ func (p *Parser) blockStmt() *BlockStmt {
 
 	p.consume(RIGHT_BRACE, "Unclosed block: Expected '}'.")
 
-	return &BlockStmt{stmts}
+	return stmts
+}
+
+// blockStmt -> "{" statement* "}"
+func (p *Parser) blockStmt() *BlockStmt {
+	return &BlockStmt{p.block()}
 }
 
 // breakStmt -> break ";"
@@ -496,7 +500,7 @@ func (p *Parser) lambda() Expr {
 	p.consume(RIGHT_PAREN, "Expect ')' after lambda arguments.")
 	p.consume(LEFT_BRACE, "Expect '{' before lambda body.")
 
-	body := p.blockStmt()
+	body := p.block()
 
 	return &Lambda{name, args, body}
 }
@@ -583,7 +587,6 @@ func (p *Parser) recover() {
 
 func (p *Parser) panic(pe *ParseError) {
 	p.errors = append(p.errors, pe)
-	log.Println(pe)
 	panic(pe)
 }
 

resolver.go

@@ -0,0 +1,188 @@
+package main
+
+type Scope map[string]bool
+
+type Resolver struct {
+	interpreter *Interpreter
+	scopes      Stack[Scope]
+}
+
+type ResolveError struct {
+	msg string
+}
+
+func (r *ResolveError) Error() string {
+	return r.msg
+}
+
+func newResolver(i *Interpreter) *Resolver {
+	return &Resolver{i, NewStack[Scope]()}
+}
+
+func (r *Resolver) resolveStmts(stmts ...Stmt) error {
+	for _, stmt := range stmts {
+		stmt.accept(r)
+	}
+
+	return nil
+}
+
+func (r *Resolver) resolveExprs(exprs ...Expr) error {
+	for _, expr := range exprs {
+		expr.accept(r)
+	}
+
+	return nil
+}
+
+func (r *Resolver) beginScope() {
+	r.scopes.Push(map[string]bool{})
+}
+
+func (r *Resolver) endScope() {
+	r.scopes.Pop()
+}
+
+func (r *Resolver) declare(token Token) {
+	if !r.scopes.Empty() {
+		r.scopes.Peek()[token.lexeme] = false
+	}
+}
+
+func (r *Resolver) define(token Token) {
+	if !r.scopes.Empty() {
+		r.scopes.Peek()[token.lexeme] = true
+	}
+}
+
+func (r *Resolver) visitBlockStmt(b *BlockStmt) {
+	r.beginScope()
+	r.resolveStmts(b.stmts...)
+	r.endScope()
+}
+
+func (r *Resolver) visitVarStmt(v *VarStmt) {
+	r.declare(v.name)
+	if v.initializer != nil {
+		r.resolveExprs(v.initializer)
+	}
+	r.define(v.name)
+}
+
+func (r *Resolver) visitVariable(v *Variable) any {
+	if !r.scopes.Empty() {
+		defined, declared := r.scopes.Peek()[v.name.lexeme]
+
+		if declared && !defined {
+			panic(&ResolveError{"Can't read local variable in its own initializer."})
+		}
+	}
+
+	r.resolveLocal(v, v.name)
+	return nil
+}
+
+func (r *Resolver) visitAssignment(a *Assign) any {
+	r.resolveExprs(a.value)
+	r.resolveLocal(a, a.variable)
+	return nil
+}
+
+func (r *Resolver) resolveLocal(expr Expr, name Token) {
+	for i := r.scopes.Size() - 1; i >= 0; i-- {
+		if _, exists := r.scopes.At(i)[name.lexeme]; exists {
+			r.interpreter.resolve(expr, r.scopes.Size()-1-i)
+			return
+		}
+	}
+}
+
+func (r *Resolver) visitFunStmt(fun *FunStmt) {
+	r.declare(fun.name)
+	r.define(fun.name)
+	r.resolveFun(fun)
+}
+
+func (r *Resolver) resolveFun(fun *FunStmt) {
+	r.beginScope()
+	for _, arg := range fun.args {
+		r.declare(arg)
+		r.define(arg)
+	}
+	r.resolveStmts(fun.body...)
+	r.endScope()
+}
+
+func (r *Resolver) visitExprStmt(es *ExprStmt) {
+	r.resolveExprs(es.expr)
+}
+
+func (r *Resolver) visitBreakStmt(b *BreakStmt) {}
+func (r *Resolver) visitEnvStmt(b *EnvStmt)     {}
+func (r *Resolver) visitIfStmt(ifs *IfStmt) {
+	r.resolveExprs(ifs.cond)
+	r.resolveStmts(ifs.then)
+	if ifs.or != nil {
+		r.resolveStmts(ifs.or)
+	}
+}
+
+func (r *Resolver) visitPrintStmt(p *PrintStmt) {
+	r.resolveExprs(p.val)
+}
+
+func (r *Resolver) visitReturnStmt(ret *ReturnStmt) {
+	if ret.value != nil {
+		r.resolveExprs(ret.value)
+	}
+}
+
+func (r *Resolver) visitWhileStmt(w *WhileStmt) {
+	r.resolveExprs(w.cond)
+	r.resolveStmts(w.body)
+}
+
+func (r *Resolver) visitBinary(b *Binary) any {
+	r.resolveExprs(b.left)
+	r.resolveExprs(b.right)
+	return nil
+}
+
+func (r *Resolver) visitCall(c *Call) any {
+	r.resolveExprs(c.callee)
+	for _, arg := range c.args {
+		r.resolveExprs(arg)
+	}
+	return nil
+}
+
+func (r *Resolver) visitGrouping(g *Grouping) any {
+	r.resolveExprs(g.expression)
+	return nil
+}
+
+func (r *Resolver) visitLambda(l *Lambda) any {
+	r.beginScope()
+	for _, arg := range l.args {
+		r.declare(arg)
+		r.define(arg)
+	}
+	r.resolveStmts(l.body...)
+	r.endScope()
+	return nil
+}
+
+func (r *Resolver) visitLiteral(l *Literal) any {
+	return nil
+}
+
+func (r *Resolver) visitLogical(l *Logical) any {
+	r.resolveExprs(l.left)
+	r.resolveExprs(l.right)
+	return nil
+}
+
+func (r *Resolver) visitUnary(u *Unary) any {
+	r.resolveExprs(u.right)
+	return nil
+}

stack.go

@@ -0,0 +1,47 @@
+package main
+
+type Stack[Item any] interface {
+	Push(Item)
+	Pop() Item
+	Peek() Item
+	At(int) Item
+	Size() int
+	Empty() bool
+}
+
+type node[Item any] struct {
+	item Item
+	next *node[Item]
+}
+
+type stack[OfType any] []OfType
+
+func NewStack[OfType any]() Stack[OfType] {
+	return &stack[OfType]{}
+}
+
+func (s *stack[Item]) Push(item Item) {
+	*s = append(*s, item)
+}
+
+func (s *stack[Item]) Pop() Item {
+	last := s.Peek()
+	*s = (*s)[:len(*s)-1]
+	return last
+}
+
+func (s *stack[Item]) At(idx int) Item {
+	return (*s)[idx]
+}
+
+func (s *stack[Item]) Peek() Item {
+	return (*s)[len(*s)-1]
+}
+
+func (s *stack[_]) Size() int {
+	return len(*s)
+}
+
+func (s *stack[_]) Empty() bool {
+	return s.Size() == 0
+}

stmt.go

@@ -39,7 +39,7 @@ type EnvStmt struct{}
 
 type IfStmt struct {
 	name Token
-	expr Expr
+	cond Expr
 	then Stmt
 	or   Stmt
 }
@@ -54,7 +54,7 @@ type BreakStmt struct{}
 type FunStmt struct {
 	name Token
 	args []Token
-	body *BlockStmt
+	body []Stmt
 }
 
 type ReturnStmt struct {

tests/functions.lox

@@ -4,6 +4,7 @@ print "native function";
 print clock();
 
 fun count(n) {
+    print n;
     if (n > 1) count(n - 1);
     print n;
 }
@@ -43,7 +44,6 @@ for (var i = 1; i <= 10; i = i + 1) {
     print fib(i);
 }
 
-
 fun makeCounter() {
     var i = 0;
 

tests/scope_and_binding.lox

@@ -0,0 +1,12 @@
+var a = "global";
+
+{
+    fun showA() {
+        print a;
+    }
+
+    showA();
+    var a = "inner v2";
+
+    showA();
+}