handle with setq special form in evaluator (#33)

evaluator/evaluator.go

@@ -166,7 +166,11 @@ func evalValueList(consCell *ast.ConsCell, env *object.Environment) []object.Obj
 		if isError(car) {
 			return []object.Object{car}
 		}
-		list = append(list, car)
+		if symbol, ok := car.(*object.Symbol); ok {
+			list = append(list, symbol.Value)
+		} else {
+			list = append(list, car)
+		}
 
 		// move to the next cons cell or return the list if the cdr is nil
 		switch cdr := consCell.Cdr().(type) {
@@ -232,6 +236,8 @@ func evalSpecialForm(sexp *ast.ConsCell, env *object.Environment) object.Object
 		return evalBackquote(sexp, env)
 	case "if":
 		return evalIf(sexp, env)
+	case "setq":
+		return evalSetq(sexp, env)
 	}
 
 	return newError("unknown special form: %s", spForm.Value)
@@ -428,3 +434,42 @@ func isTruthy(obj object.Object) bool {
 		return true
 	}
 }
+
+func evalSetq(consCell *ast.ConsCell, env *object.Environment) object.Object {
+	spForm, ok := consCell.Car().(*ast.SpecialForm)
+	if !ok {
+		return newError("expect special form, got %T", consCell.Car())
+	}
+	if spForm.Token.Type != token.SETQ {
+		return newError("expect special form setq, got %s", spForm.Token.Type)
+	}
+
+	cdr, ok := consCell.Cdr().(*ast.ConsCell)
+	if !ok {
+		return newError("not defined name of symbol")
+	}
+
+	symbolName, ok := cdr.Car().(*ast.Symbol)
+	if !ok {
+		return newError("expect symbol, got %T", cdr.Car())
+	}
+
+	cddr, ok := cdr.Cdr().(*ast.ConsCell)
+	if !ok {
+		return newError("not defined value of symbol")
+	}
+
+	value := Eval(cddr.Car(), env)
+	if isError(value) {
+		return value
+	}
+
+	symbol := &object.Symbol{
+		Name:  symbolName.Value,
+		Value: value,
+	}
+
+	env.Set(symbolName.Value, symbol)
+
+	return symbol
+}

evaluator/evaluator_test.go

@@ -19,15 +19,30 @@ func testEval(input string) object.Object {
 
 func testIntegerObject(t *testing.T, obj object.Object, expected int64) bool {
 	result, ok := obj.(*object.Integer)
-	if !ok {
-		t.Errorf("object is not Integer. got=%T (%+v)", obj, obj)
-		return false
+	if ok {
+		if result.Value != expected {
+			t.Errorf("object has wrong value. got=%d, want=%d", result.Value, expected)
+			return false
+		}
+		return true
 	}
-	if result.Value != expected {
-		t.Errorf("object has wrong value. got=%d, want=%d", result.Value, expected)
-		return false
+
+	symbol, ok := obj.(*object.Symbol)
+	if ok {
+		integer, ok := symbol.Value.(*object.Integer)
+		if !ok {
+			t.Errorf("object is not Integer. got=%T (%+v)", result.Value, result.Value)
+			return false
+		}
+		if integer.Value != expected {
+			t.Errorf("object has wrong value. got=%d, want=%d", integer.Value, expected)
+			return false
+		}
+		return true
 	}
-	return true
+
+	t.Errorf("object is not Integer. got=%T (%+v)", obj, obj)
+	return false
 }
 
 func TestEvalIntegerExpression(t *testing.T) {
@@ -201,3 +216,20 @@ func TestIfExpression(t *testing.T) {
 		}
 	}
 }
+
+func TestSetqExpression(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected int64
+	}{
+		{"(setq x 10) x", 10},
+		{"(setq x 10) (setq x 20) x", 20},
+		{"(setq x 10) (setq y 20) (+ x y)", 30},
+		{"(setq x (+ 1 1)) x", 2},
+	}
+
+	for _, tt := range tests {
+		evaluated := testEval(tt.input)
+		testIntegerObject(t, evaluated, tt.expected)
+	}
+}