Return statements

evaluator/evaluator.go

@@ -16,17 +16,21 @@ func Eval(node ast.Node) object.Object {
 
 	// Statements
 	case *ast.Program:
-		return evalStatements(node.Statements)
+		return evalProgram(node)
 
 	case *ast.ExpressionStatement:
 		return Eval(node.Expression)
 
 	case *ast.BlockStatement:
-		return evalStatements(node.Statements)
+		return evalBlockStatements(node)
 
 	case *ast.IfExpression:
 		return evalIfExpression(node)
 
+	case *ast.ReturnStatement:
+		val := Eval(node.ReturnValue)
+		return &object.ReturnValue{Value: val}
+
 	// Expressions
 	case *ast.IntegerLiteral:
 		return &object.Integer{Value: node.Value}
@@ -48,11 +52,29 @@ func Eval(node ast.Node) object.Object {
 	return nil
 }
 
-func evalStatements(stmts []ast.Statement) object.Object {
+func evalProgram(program *ast.Program) object.Object {
 	var result object.Object
 
-	for _, statement := range stmts {
+	for _, statement := range program.Statements {
 		result = Eval(statement)
+
+		if returnValue, ok := result.(*object.ReturnValue); ok {
+			return returnValue.Value
+		}
+	}
+
+	return result
+}
+
+func evalBlockStatements(block *ast.BlockStatement) object.Object {
+	var result object.Object
+
+	for _, statement := range block.Statements {
+		result = Eval(statement)
+
+		if result != nil && result.Type() == object.RETURN_VALUE_OBJ {
+			return result
+		}
 	}
 
 	return result

evaluator/evaluator_test.go

@@ -111,6 +111,34 @@ func TestIfElseExpression(t *testing.T) {
 	}
 }
 
+func TestReturnStatements(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"return 10;", 10},
+		{"return 10; 9;", 10},
+		{"return 2 * 5; 9;", 10},
+		{"9; return 2 * 5; 9;", 10},
+		{`
+				if (10 > 1) {
+				  if (10 > 1) {
+					return 10;
+				  }
+				
+				  return 1;
+				}
+			`,
+			10,
+		},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}
+
 func testEval(input string) object.Object {
 	l := lexer.New(input)
 	p := parser.New(l)

object/object.go

@@ -8,6 +8,7 @@ const (
 	INTEGER_OBJ      = "INTEGER"
 	BOOLEAN_OBJ      = "BOOLEAN"
 	NULL_OBJ         = "NULL"
+	RETURN_VALUE_OBJ = "RETURN_VALUE"
 )
 
 type Object interface {
@@ -46,3 +47,15 @@ func (n *Null) Type() ObjectType {
 func (n *Null) Inspect() string {
 	return "null"
 }
+
+type ReturnValue struct {
+	Value Object
+}
+
+func (rv ReturnValue) Type() ObjectType {
+	return RETURN_VALUE_OBJ
+}
+
+func (rv ReturnValue) Inspect() string {
+	return rv.Value.Inspect()
+}