len buiiltin function!!

evaluator/builtins.go

@@ -0,0 +1,21 @@
+package evaluator
+
+import "github.com/Jonak-Adipta-Kalita/JAK-Programming-Language/object"
+
+var builtins = map[string]*object.Builtin{
+	"len": &object.Builtin{
+		Fn: func(args ...object.Object) object.Object {
+			if len(args) != 1 {
+				return newError("wrong number of arguments. got=%d, want=1",
+					len(args))
+			}
+			switch arg := args[0].(type) {
+			case *object.String:
+				return &object.Integer{Value: int64(len(arg.Value))}
+			default:
+				return newError("argument to `len` not supported, got %s",
+					args[0].Type())
+			}
+		},
+	},
+}

evaluator/evaluator.go

@@ -96,11 +96,15 @@ func evalIdentifier(
 	node *ast.Identifier,
 	env *object.Environment,
 ) object.Object {
-	val, ok := env.Get(node.Value)
-	if !ok {
-		return newError("identifier not found: " + node.Value)
+	if val, ok := env.Get(node.Value); ok {
+		return val
 	}
-	return val
+
+	if builtin, ok := builtins[node.Value]; ok {
+		return builtin
+	}
+
+	return newError("identifier not found: " + node.Value)
 }
 
 func evalProgram(program *ast.Program, env *object.Environment) object.Object {
@@ -278,13 +282,16 @@ func isError(obj object.Object) bool {
 }
 
 func applyFunction(fn object.Object, args []object.Object) object.Object {
-	function, ok := fn.(*object.Function)
-	if !ok {
+	switch fn := fn.(type) {
+	case *object.Function:
+		extendedEnv := extendFunctionEnv(fn, args)
+		evaluated := Eval(fn.Body, extendedEnv)
+		return unwrapReturnValue(evaluated)
+	case *object.Builtin:
+		return fn.Fn(args...)
+	default:
 		return newError("not a function: %s", fn.Type())
 	}
-	extendedEnv := extendFunctionEnv(function, args)
-	evaluated := Eval(function.Body, extendedEnv)
-	return unwrapReturnValue(evaluated)
 }
 
 func extendFunctionEnv(

object/object.go

@@ -25,6 +25,8 @@ const (
 
 	RETURN_VALUE_OBJ = "RETURN_VALUE"
 	FUNCTION_OBJ     = "FUNCTION"
+
+	BUILTIN_OBJ = "BUILTIN"
 )
 
 type Boolean struct {
@@ -88,3 +90,12 @@ type String struct {
 
 func (s *String) Type() ObjectType { return STRING_OBJ }
 func (s *String) Inspect() string  { return s.Value }
+
+type BuiltinFunction func(args ...Object) Object
+
+type Builtin struct {
+	Fn BuiltinFunction
+}
+
+func (b *Builtin) Type() ObjectType { return BUILTIN_OBJ }
+func (b *Builtin) Inspect() string  { return "builtin function" }