blocks, env

.gitignore

@@ -0,0 +1 @@
+glox

ast_string.go

@@ -7,11 +7,12 @@ import (
 
 type AstStringer struct {
 	str   strings.Builder
+	stmts []Stmt
 }
 
-func (as AstStringer) String(stmts []Stmt) string {
+func (as AstStringer) String() string {
 
-	for _, stmt := range stmts {
+	for _, stmt := range as.stmts {
 		stmt.accept(&as)
 	}
 
@@ -80,3 +81,14 @@ func (as *AstStringer) visitVarStmt(vs *VarStmt) {
 		as.str.WriteString(fmt.Sprintf("(var %v)", vs.name.literal))
 	}
 }
+
+func (as *AstStringer) visitBlockStmt(b *BlockStmt) {
+	as.str.WriteString("(block ")
+
+	for _, stmt := range b.stmts {
+		stmt.accept(as)
+	}
+
+	as.str.WriteString(")")
+
+}

env.go

@@ -0,0 +1,37 @@
+package main
+
+type Environment struct {
+	values map[string]any
+	parent *Environment
+}
+
+func newEnvironment(parent *Environment) *Environment {
+	return &Environment{values: map[string]any{}, parent: parent}
+}
+
+func (env *Environment) get(key string) any {
+	if found, ok := env.values[key]; ok {
+		return found
+	}
+
+	if env.parent != nil {
+		return env.parent.get(key)
+	}
+
+	return nil
+}
+
+func (env *Environment) exists(key string) bool {
+	_, ok := env.values[key]
+
+	if !ok && env.parent != nil {
+		return env.parent.exists(key)
+	}
+
+	return ok
+
+}
+
+func (env *Environment) set(key string, val any) {
+	env.values[key] = val
+}

glox.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bufio"
+	"fmt"
 	"log"
 	"os"
 )
@@ -32,7 +33,7 @@ func (gl *Glox) runPrompt() {
 		if !scanner.Scan() {
 			break
 		}
-		gl.run(scanner.Bytes(), true)
+		gl.run(scanner.Bytes())
 	}
 }
 
@@ -43,32 +44,15 @@ func (gl *Glox) runFile(path string) {
 		log.Fatal(err)
 	}
 
-	runErrors := gl.run(file, false)
-
-	if len(runErrors) != 0 {
-		for _, e := range runErrors {
-			log.Print(e)
-		}
-
-		os.Exit(1)
-	}
-
+	gl.run(file)
 }
 
-func (gl *Glox) run(source []byte, interactive bool) []error {
-	tokens, err := newScanner(source).scan()
+func (gl *Glox) run(source []byte) {
+	tokens, _ := newScanner(source).scan()
 
-	if err != nil {
-		return []error{err}
-	}
+	stmts, _ := newParser(tokens).parse()
 
-	stmts, parseErrs := newParser(tokens).parse()
+	fmt.Println(AstStringer{stmts: stmts})
 
-	if len(parseErrs) != 0 && !interactive {
-		return parseErrs
-	}
-
-	println(AstStringer{}.String(stmts))
-
-	return gl.Interpreter.interpret(stmts)
+	gl.Interpreter.interpret(stmts)
 }

interpreter.go

@@ -7,7 +7,7 @@ import (
 )
 
 type Interpreter struct {
-	env    map[string]any
+	env    *Environment
 	errors []error
 }
 
@@ -21,7 +21,7 @@ func (re *RuntimeError) Error() string {
 }
 
 func newInterpreter() *Interpreter {
-	return &Interpreter{env: make(map[string]any)}
+	return &Interpreter{env: newEnvironment(nil)}
 }
 
 func (i *Interpreter) interpret(stmts []Stmt) []error {
@@ -118,25 +118,30 @@ func (i *Interpreter) visitUnary(u *Unary) any {
 }
 
 func (i *Interpreter) visitVariable(v *Variable) any {
-	if found, ok := i.env[v.name.lexeme]; ok {
-		return found
+
+	val := i.env.get(v.name.lexeme)
+
+	if val == nil {
+		i.panic(&RuntimeError{v.name, fmt.Sprintf("Can't evaluate: Undefined variable '%s'.", v.name.lexeme)})
+		return nil
 	}
 
-	i.panic(&RuntimeError{v.name, fmt.Sprintf("Undefined variable '%s'.", v.name.lexeme)})
-
-	return nil
+	return val
 }
 
 func (i *Interpreter) visitAssignment(a *Assign) any {
-	if _, ok := i.env[a.variable.lexeme]; ok {
-		val := i.evaluate(a.value)
-		i.env[a.variable.lexeme] = val
-		return val
-	}
 
-	i.panic(&RuntimeError{a.variable, fmt.Sprintf("Undefined variable '%s'.", a.variable.lexeme)})
+	if !i.env.exists(a.variable.lexeme) {
+		i.panic(&RuntimeError{a.variable, fmt.Sprintf("Can't assign: undefined variable '%s'.", a.variable.lexeme)})
 
 		return nil
+	}
+
+	val := i.evaluate(a.value)
+
+	i.env.set(a.variable.lexeme, val)
+
+	return val
 }
 
 func (i *Interpreter) visitPrintStmt(p *PrintStmt) {
@@ -155,7 +160,19 @@ func (i *Interpreter) visitVarStmt(v *VarStmt) {
 		val = i.evaluate(v.initializer)
 	}
 
-	i.env[v.name.lexeme] = val
+	i.env.set(v.name.lexeme, val)
+}
+
+func (i *Interpreter) visitBlockStmt(b *BlockStmt) {
+
+	parentEnv := i.env
+	i.env = newEnvironment(parentEnv)
+
+	for _, stmt := range b.stmts {
+		stmt.accept(i)
+	}
+
+	i.env = parentEnv
 }
 
 func (i *Interpreter) panic(re *RuntimeError) {

parser.go

@@ -66,11 +66,16 @@ func (p *Parser) varDecl() Stmt {
 	return &VarStmt{name, initializer}
 }
 
-// statement -> exprStmt | printStmt
+// statement -> exprStmt | printStmt | block
 func (p *Parser) statement() Stmt {
 	if p.match(PRINT) {
 		return p.printStmt()
 	}
+
+	if p.match(LEFT_BRACE) {
+		return p.block()
+	}
+
 	return p.exprStmt()
 }
 
@@ -88,6 +93,19 @@ func (p *Parser) printStmt() Stmt {
 	return &PrintStmt{expr}
 }
 
+// block -> "{" statement* "}"
+func (p *Parser) block() Stmt {
+
+	stmts := []Stmt{}
+	for !p.check(RIGHT_BRACE) {
+		stmts = append(stmts, p.declaration())
+	}
+
+	p.consume(RIGHT_BRACE, "Unclosed block: Expected '}'.")
+
+	return &BlockStmt{stmts}
+}
+
 // expression -> assignment
 func (p *Parser) expression() Expr {
 	return p.assignment()
@@ -199,7 +217,7 @@ func (p *Parser) primary() Expr {
 		return &Grouping{expr}
 	}
 
-	p.panic(&ParseError{p.peek(), "Expect expression"})
+	// p.panic(&ParseError{p.peek(), "Expect expression"})
 
 	return nil
 }

stmt.go

@@ -1,9 +1,10 @@
 package main
 
 type StmtVisitor interface {
-	visitPrintStmt(p *PrintStmt)
-	visitExprStmt(es *ExprStmt)
 	visitVarStmt(v *VarStmt)
+	visitExprStmt(es *ExprStmt)
+	visitPrintStmt(p *PrintStmt)
+	visitBlockStmt(b *BlockStmt)
 }
 
 type Stmt interface {
@@ -24,9 +25,14 @@ type VarStmt struct {
 	initializer Expr
 }
 
-func (p *PrintStmt) stmt() {}
-func (es *ExprStmt) stmt() {}
+type BlockStmt struct {
+	stmts []Stmt
+}
+
 func (vs *VarStmt) stmt()  {}
+func (es *ExprStmt) stmt() {}
+func (p *PrintStmt) stmt() {}
+func (b *BlockStmt) stmt() {}
 
 func (p *PrintStmt) accept(v StmtVisitor) {
 	v.visitPrintStmt(p)
@@ -39,3 +45,7 @@ func (se *ExprStmt) accept(v StmtVisitor) {
 func (vs *VarStmt) accept(v StmtVisitor) {
 	v.visitVarStmt(vs)
 }
+
+func (b *BlockStmt) accept(v StmtVisitor) {
+	v.visitBlockStmt(b)
+}

tests/blocks.lox

@@ -0,0 +1,22 @@
+var a = "global a";
+var b = "global b";
+var c = "global c";
+
+{
+    var a = "outer a";
+    var b = "outer b";
+    {
+        var a = "inner a";
+        print a;
+        print b;
+        print c;
+    }
+
+    print a;
+    print b;
+    print c;
+}
+
+print a;
+print b;
+print c;