Add resolving and binding

errors/logger.go

@@ -8,17 +8,23 @@ type Logger interface {
 	RuntimeError(message string)
 }
 
-type mockErrorLogger struct{}
+type mockErrorLogger struct {
+	Errors        []string
+	RuntimeErrors []string
+}
 
 func (el *mockErrorLogger) Error(line int, message string) {
+	el.Errors = append(el.Errors, message)
 }
 
 func (el *mockErrorLogger) ErrorAtToken(t token.Token, message string) {
+	el.Errors = append(el.Errors, message)
 }
 
 func (el *mockErrorLogger) RuntimeError(message string) {
+	el.RuntimeErrors = append(el.RuntimeErrors, message)
 }
 
 func NewMockErrorLogger() *mockErrorLogger {
-	return &mockErrorLogger{}
+	return &mockErrorLogger{[]string{}, []string{}}
 }

interpreter/environment.go

@@ -17,6 +17,21 @@ func (e *environment) define(name string, value any) {
 	e.values[name] = value
 }
 
+// ancestor returns the environment at a given distance.
+func (e *environment) ancestor(distance int) *environment {
+	env := e
+	for i := 0; i < distance; i++ {
+		env = env.enclosing
+	}
+
+	return env
+}
+
+// getAt gets the value of a variable at a given distance.
+func (e *environment) getAt(distance int, name string) any {
+	return e.ancestor(distance).values[name]
+}
+
 // get gets the value of a variable in the environment.
 func (e *environment) get(name string) any {
 	value, ok := e.values[name]
@@ -31,6 +46,11 @@ func (e *environment) get(name string) any {
 	return value
 }
 
+// assignAt assigns a new value to a variable at a given distance.
+func (e *environment) assignAt(distance int, name string, value any) {
+	e.ancestor(distance).values[name] = value
+}
+
 // assign assigns a new value to a variable in the environment.
 func (e *environment) assign(name string, value any) {
 	_, ok := e.values[name]

interpreter/interpreter.go

@@ -19,6 +19,7 @@ type Interpreter struct {
 	errLogger errors.Logger
 	env       *environment
 	globals   *environment
+	locals    map[ast.Expr]int
 }
 
 // New creates a new Interpreter.
@@ -34,7 +35,7 @@ func New(el errors.Logger) *Interpreter {
 
 	globals.define("clock", clockCallable)
 
-	return &Interpreter{el, globals, globals}
+	return &Interpreter{el, globals, globals, make(map[ast.Expr]int)}
 }
 
 // Interpret interprets the AST.
@@ -134,7 +135,14 @@ func (i *Interpreter) VisitErrorExpr(e *ast.ErrorExpr) any {
 // VisitAssignExpr visits an AssignExpr.
 func (i *Interpreter) VisitAssignExpr(a *ast.AssignExpr) any {
 	value := i.evaluate(a.Value)
-	i.env.assign(a.Name.Lexeme, value)
+
+	depth, ok := i.locals[a]
+	if ok {
+		i.env.assignAt(depth, a.Name.Lexeme, value)
+	} else {
+		i.globals.assign(a.Name.Lexeme, value)
+	}
+
 	return value
 }
 
@@ -256,7 +264,17 @@ func (i *Interpreter) VisitCallExpr(c *ast.CallExpr) any {
 
 // VisitVariableExpr visits a VariableExpr.
 func (i *Interpreter) VisitVariableExpr(v *ast.VariableExpr) any {
-	return i.env.get(v.Name.Lexeme)
+	return i.lookUpVariable(&v.Name, v)
+}
+
+// lookUpVariable looks up a variable.
+func (i *Interpreter) lookUpVariable(name *token.Token, expr ast.Expr) any {
+	depth, ok := i.locals[expr]
+	if ok {
+		return i.env.getAt(depth, name.Lexeme)
+	}
+
+	return i.globals.get(name.Lexeme)
 }
 
 // checkNumberOperands checks if the operands are numbers.
@@ -304,6 +322,11 @@ func (i *Interpreter) execute(s ast.Stmt) {
 	s.Accept(i)
 }
 
+// resolve resolves the variables depths of an expression
+func (i *Interpreter) Resolve(e ast.Expr, depth int) {
+	i.locals[e] = depth
+}
+
 // executeBlock executes a block of statements.
 func (i *Interpreter) executeBlock(stmts []ast.Stmt, env *environment) {
 	previous := i.env

interpreter/interpreter_test.go

@@ -437,22 +437,27 @@ func TestInterpretBlockStatement(t *testing.T) {
 		outC <- buf.String()
 	}()
 
+	le := &ast.LiteralExpr{Value: 42.0}
+	ve := &ast.VariableExpr{
+		Name: token.Token{Type: token.IDENTIFIER, Lexeme: "foo"},
+	}
+
 	// begin unit test
 	i := New(errors.NewMockErrorLogger())
 	block := &ast.BlockStmt{
 		Statements: []ast.Stmt{
 			&ast.VarStmt{
 				Name:        token.Token{Type: token.IDENTIFIER, Lexeme: "foo"},
-				Initializer: &ast.LiteralExpr{Value: 42.0},
+				Initializer: le,
 			},
 			&ast.PrintStmt{
-				Expression: &ast.VariableExpr{
+				Expression: ve,
-					Name: token.Token{Type: token.IDENTIFIER, Lexeme: "foo"},
-				},
 			},
 		},
 	}
 
+	i.locals[le] = 0
+	i.locals[ve] = 0
 	i.VisitBlockStmt(block)
 	_, found := i.env.values["foo"]
 	if found {
@@ -655,10 +660,13 @@ func TestInterpretFunctionCall(t *testing.T) {
 
 func TestInterpretFunctionCallWithArguments(t *testing.T) {
 	i := New(errors.NewMockErrorLogger())
+
+	ve := &ast.VariableExpr{Name: token.Token{Type: token.IDENTIFIER, Lexeme: "a"}}
+
 	functionStmt := &ast.FunctionStmt{
 		Name:   token.Token{Type: token.IDENTIFIER, Lexeme: "foo"},
 		Params: []token.Token{{Type: token.IDENTIFIER, Lexeme: "a"}},
-		Body:   []ast.Stmt{&ast.BlockStmt{Statements: []ast.Stmt{&ast.PrintStmt{Expression: &ast.VariableExpr{Name: token.Token{Type: token.IDENTIFIER, Lexeme: "a"}}}}}},
+		Body:   []ast.Stmt{&ast.BlockStmt{Statements: []ast.Stmt{&ast.PrintStmt{Expression: ve}}}},
 	}
 
 	i.VisitFunctionStmt(functionStmt)
@@ -670,6 +678,7 @@ func TestInterpretFunctionCallWithArguments(t *testing.T) {
 		},
 	}
 
+	i.locals[ve] = 0
 	i.VisitCallExpr(callExpr)
 }
 

lox/lox.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"golox/interpreter"
 	"golox/parser"
+	"golox/resolver"
 	"golox/scanner"
 	"golox/token"
 	"os"
@@ -100,5 +101,13 @@ func (l *Lox) run(source string) {
 		return
 	}
 
+	resolver := resolver.New(l.interpreter, l)
+	resolver.Resolve(stmts)
+
+	// Stop if there was a resolution error.
+	if l.hadError {
+		return
+	}
+
 	l.interpreter.Interpret(stmts)
 }

resolver/resolver.go

@@ -0,0 +1,261 @@
+package resolver
+
+import (
+	"golox/ast"
+	"golox/errors"
+	"golox/interpreter"
+	"golox/token"
+)
+
+// FuncType represents the type of a function.
+type FuncType int
+
+const (
+	// NoneFuncType represents a function with no type.
+	NoneFuncType FuncType = iota
+	// FunctionFuncType represents a function.
+	FunctionFuncType
+	// MethodFuncType represents a method.
+	MethodFuncType
+	// InitializerFuncType represents an initializer.
+	InitializerFuncType
+)
+
+// Resolver implements variable resolution for the AST.
+type Resolver struct {
+	errLogger   errors.Logger
+	interpreter *interpreter.Interpreter
+	scopes      []map[string]bool
+	currFunc    FuncType
+}
+
+// New creates a new Resolver.
+func New(i *interpreter.Interpreter, el errors.Logger) *Resolver {
+	return &Resolver{el, i, []map[string]bool{}, NoneFuncType}
+}
+
+// VisitBlockStmt visits a block statement.
+func (r *Resolver) VisitBlockStmt(bs *ast.BlockStmt) any {
+	r.beginScope()
+	r.Resolve(bs.Statements)
+	r.endScope()
+	return nil
+}
+
+// Resolve resolves the variables for each statements in stmts.
+func (r *Resolver) Resolve(stmts []ast.Stmt) {
+	for _, stmt := range stmts {
+		r.resolveStmt(stmt)
+	}
+}
+
+// resolveStmt resolves a statement.
+func (r *Resolver) resolveStmt(stmt ast.Stmt) {
+	stmt.Accept(r)
+}
+
+// resolveExpr resolves an expression.
+func (r *Resolver) resolveExpr(expr ast.Expr) {
+	expr.Accept(r)
+}
+
+// beginScope begins a new scope.
+func (r *Resolver) beginScope() {
+	r.scopes = append(r.scopes, map[string]bool{})
+}
+
+// endScope ends the current scope.
+func (r *Resolver) endScope() {
+	r.scopes = r.scopes[:len(r.scopes)-1]
+}
+
+// visitVarStmt visits a variable statement.
+func (r *Resolver) VisitVarStmt(vs *ast.VarStmt) any {
+	r.declare(&vs.Name)
+	if vs.Initializer != nil {
+		r.resolveExpr(vs.Initializer)
+	}
+	r.define(&vs.Name)
+
+	return nil
+}
+
+// declare declares a variable in the current scope.
+func (r *Resolver) declare(name *token.Token) {
+	if len(r.scopes) == 0 {
+		return
+	}
+
+	scope := r.scopes[len(r.scopes)-1]
+	if _, ok := scope[name.Lexeme]; ok {
+		r.errLogger.ErrorAtToken(*name, "Variable with this name already declared in this scope.")
+	}
+	scope[name.Lexeme] = false
+}
+
+// define defines a variable in the current scope.
+func (r *Resolver) define(name *token.Token) {
+	if len(r.scopes) == 0 {
+		return
+	}
+
+	r.scopes[len(r.scopes)-1][name.Lexeme] = true
+}
+
+// VisitVariableExpr visits a variable expression.
+func (r *Resolver) VisitVariableExpr(ve *ast.VariableExpr) any {
+	if len(r.scopes) > 0 {
+		if _, ok := r.scopes[len(r.scopes)-1][ve.Name.Lexeme]; ok && !r.scopes[len(r.scopes)-1][ve.Name.Lexeme] {
+			r.errLogger.ErrorAtToken(ve.Name, "Cannot read local variable in its own initializer.")
+		}
+	}
+
+	r.resolveLocal(ve, &ve.Name)
+
+	return nil
+}
+
+// resolveLocal resolves a local variable.
+func (r *Resolver) resolveLocal(expr ast.Expr, name *token.Token) {
+	for i := len(r.scopes) - 1; i >= 0; i-- {
+		if _, ok := r.scopes[i][name.Lexeme]; ok {
+			r.interpreter.Resolve(expr, len(r.scopes)-1-i)
+			return
+		}
+	}
+}
+
+// VisitAssignExpr visits an assignment expression.
+func (r *Resolver) VisitAssignExpr(ae *ast.AssignExpr) any {
+	r.resolveExpr(ae.Value)
+	r.resolveLocal(ae, &ae.Name)
+
+	return nil
+}
+
+// VisitFunctionStmt visits a function statement.
+func (r *Resolver) VisitFunctionStmt(fs *ast.FunctionStmt) any {
+	r.declare(&fs.Name)
+	r.define(&fs.Name)
+
+	r.resolveFunction(fs, FunctionFuncType)
+
+	return nil
+}
+
+// resolveFunction resolves a function.
+func (r *Resolver) resolveFunction(fs *ast.FunctionStmt, t FuncType) {
+	enclosingFunc := r.currFunc
+	r.currFunc = t
+
+	r.beginScope()
+	for _, param := range fs.Params {
+		r.declare(&param)
+		r.define(&param)
+	}
+
+	r.Resolve(fs.Body)
+	r.endScope()
+
+	r.currFunc = enclosingFunc
+}
+
+// VisitExpressionStmt visits an expression statement.
+func (r *Resolver) VisitExpressionStmt(es *ast.ExpressionStmt) any {
+	r.resolveExpr(es.Expression)
+	return nil
+}
+
+// VisitIfStmt visits an if statement.
+func (r *Resolver) VisitIfStmt(is *ast.IfStmt) any {
+	r.resolveExpr(is.Condition)
+	r.resolveStmt(is.ThenBranch)
+	if is.ElseBranch != nil {
+		r.resolveStmt(is.ElseBranch)
+	}
+
+	return nil
+}
+
+// VisitPrintStmt visits a print statement.
+func (r *Resolver) VisitPrintStmt(ps *ast.PrintStmt) any {
+	r.resolveExpr(ps.Expression)
+
+	return nil
+}
+
+// VisitReturnStmt visits a return statement.
+func (r *Resolver) VisitReturnStmt(rs *ast.ReturnStmt) any {
+	if r.currFunc == NoneFuncType {
+		r.errLogger.ErrorAtToken(rs.Keyword, "Cannot return from top-level code.")
+	}
+
+	if rs.Value != nil {
+		r.resolveExpr(rs.Value)
+	}
+
+	return nil
+}
+
+// VisitWhileStmt visits a while statement.
+func (r *Resolver) VisitWhileStmt(ws *ast.WhileStmt) any {
+	r.resolveExpr(ws.Condition)
+	r.resolveStmt(ws.Body)
+
+	return nil
+}
+
+// VisitErrorStmt visits an error statement.
+func (r *Resolver) VisitErrorStmt(es *ast.ErrorStmt) any {
+	return nil
+}
+
+// VisitBinaryExpr visits a binary expression.
+func (r *Resolver) VisitBinaryExpr(be *ast.BinaryExpr) any {
+	r.resolveExpr(be.Left)
+	r.resolveExpr(be.Right)
+
+	return nil
+}
+
+// VisitCallExpr visits a call expression.
+func (r *Resolver) VisitCallExpr(ce *ast.CallExpr) any {
+	r.resolveExpr(ce.Callee)
+	for _, arg := range ce.Arguments {
+		r.resolveExpr(arg)
+	}
+
+	return nil
+}
+
+// VisitGroupingExpr visits a grouping expression.
+func (r *Resolver) VisitGroupingExpr(ge *ast.GroupingExpr) any {
+	r.resolveExpr(ge.Expression)
+
+	return nil
+}
+
+// VisitLiteralExpr visits a literal expression.
+func (r *Resolver) VisitLiteralExpr(le *ast.LiteralExpr) any {
+	return nil
+}
+
+// VisitLogicalExpr visits a logical expression.
+func (r *Resolver) VisitLogicalExpr(le *ast.LogicalExpr) any {
+	r.resolveExpr(le.Left)
+	r.resolveExpr(le.Right)
+
+	return nil
+}
+
+// VisitUnaryExpr visits a unary expression.
+func (r *Resolver) VisitUnaryExpr(ue *ast.UnaryExpr) any {
+	r.resolveExpr(ue.Right)
+
+	return nil
+}
+
+// VisitErrorExpr visits an error statement.
+func (r *Resolver) VisitErrorExpr(ee *ast.ErrorExpr) any {
+	return nil
+}

resolver/resolver_test.go

@@ -0,0 +1,276 @@
+package resolver
+
+import (
+	"testing"
+
+	"golox/ast"
+	"golox/errors"
+	"golox/interpreter"
+	"golox/token"
+)
+
+func TestResolver_VisitBlockStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	blockStmt := &ast.BlockStmt{
+		Statements: []ast.Stmt{},
+	}
+
+	resolver.VisitBlockStmt(blockStmt)
+
+	if len(resolver.scopes) != 0 {
+		t.Errorf("expected scopes to be empty, got %v", resolver.scopes)
+	}
+}
+
+func TestResolver_VisitVarStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	varStmt := &ast.VarStmt{
+		Name:        token.Token{Lexeme: "a"},
+		Initializer: nil,
+	}
+
+	resolver.VisitVarStmt(varStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitVariableExpr(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	varExpr := &ast.VariableExpr{
+		Name: token.Token{Lexeme: "a"},
+	}
+
+	resolver.VisitVariableExpr(varExpr)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitAssignExpr(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	assignExpr := &ast.AssignExpr{
+		Name:  token.Token{Lexeme: "a"},
+		Value: &ast.LiteralExpr{Value: 42},
+	}
+
+	resolver.VisitAssignExpr(assignExpr)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitFunctionStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	funcStmt := &ast.FunctionStmt{
+		Name:   token.Token{Lexeme: "foo"},
+		Params: []token.Token{},
+		Body:   []ast.Stmt{},
+	}
+
+	resolver.VisitFunctionStmt(funcStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitReturnStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	returnStmt := &ast.ReturnStmt{
+		Keyword: token.Token{Lexeme: "return"},
+		Value:   &ast.LiteralExpr{Value: 42},
+	}
+
+	resolver.currFunc = FunctionFuncType
+	resolver.VisitReturnStmt(returnStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitIfStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	ifStmt := &ast.IfStmt{
+		Condition: &ast.LiteralExpr{Value: true},
+		ThenBranch: &ast.BlockStmt{
+			Statements: []ast.Stmt{},
+		},
+		ElseBranch: nil,
+	}
+
+	resolver.VisitIfStmt(ifStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitWhileStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	whileStmt := &ast.WhileStmt{
+		Condition: &ast.LiteralExpr{Value: true},
+		Body: &ast.BlockStmt{
+			Statements: []ast.Stmt{},
+		},
+	}
+
+	resolver.VisitWhileStmt(whileStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_VisitExpressionStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	exprStmt := &ast.ExpressionStmt{
+		Expression: &ast.LiteralExpr{Value: 42},
+	}
+
+	resolver.VisitExpressionStmt(exprStmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_Resolve(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	stmts := []ast.Stmt{
+		&ast.BlockStmt{
+			Statements: []ast.Stmt{
+				&ast.VarStmt{
+					Name:        token.Token{Lexeme: "a"},
+					Initializer: nil,
+				},
+				&ast.VarStmt{
+					Name:        token.Token{Lexeme: "a"},
+					Initializer: nil,
+				},
+			},
+		},
+	}
+
+	resolver.Resolve(stmts)
+
+	if len(logger.Errors) != 1 {
+		t.Errorf("expected 1 error, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_ResolveStmt(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	stmt := &ast.VarStmt{
+		Name:        token.Token{Lexeme: "a"},
+		Initializer: nil,
+	}
+
+	resolver.resolveStmt(stmt)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_ResolveExpr(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	expr := &ast.LiteralExpr{Value: 42}
+
+	resolver.resolveExpr(expr)
+
+	if len(logger.Errors) != 0 {
+		t.Errorf("expected no errors, got %v", logger.Errors)
+	}
+}
+
+func TestResolver_Declare(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	resolver.beginScope()
+	resolver.declare(&token.Token{Lexeme: "a"})
+
+	if len(resolver.scopes) != 1 {
+		t.Errorf("expected 1 scope, got %v", resolver.scopes)
+	}
+}
+
+func TestResolver_Define(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	resolver.beginScope()
+	resolver.define(&token.Token{Lexeme: "a"})
+
+	if len(resolver.scopes) != 1 {
+		t.Errorf("expected 1 scope, got %v", resolver.scopes)
+	}
+}
+
+func TestResolver_BeginScope(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	resolver.beginScope()
+
+	if len(resolver.scopes) != 1 {
+		t.Errorf("expected 1 scope, got %v", resolver.scopes)
+	}
+}
+
+func TestResolver_EndScope(t *testing.T) {
+	logger := errors.NewMockErrorLogger()
+	interp := &interpreter.Interpreter{}
+	resolver := New(interp, logger)
+
+	resolver.beginScope()
+	resolver.endScope()
+
+	if len(resolver.scopes) != 0 {
+		t.Errorf("expected 0 scopes, got %v", resolver.scopes)
+	}
+}

testdata/closure.lox

@@ -0,0 +1,10 @@
+var a = "global";
+{
+  fun showA() {
+    print a;
+  }
+
+  showA();
+  var a = "block";
+  showA();
+}