further improvements

internal/evaluator/evaluator.go

@@ -126,7 +126,7 @@ func Eval(node ast.Node, env *object.Environment) object.Object {
 	case *ast.FunctionLiteral:
 		params := node.Parameters
 		body := node.Body
-		return &object.Function{Parameters: params, Env: env, Body: body}
+		return object.Function{Parameters: params, Env: env, Body: body}
 
 	// Expressions
 	case *ast.IntegerLiteral:
@@ -560,12 +560,12 @@ func evalExpressions(exps []ast.Expression, env *object.Environment) []object.Ob
 func applyFunction(fn object.Object, args []object.Object) object.Object {
 	switch fn := fn.(type) {
 
-	case *object.Function:
+	case object.Function:
 		extendedEnv := extendFunctionEnv(fn, args)
 		evaluated := Eval(fn.Body, extendedEnv)
 		return unwrapReturnValue(evaluated)
 
-	case *object.Builtin:
+	case object.Builtin:
 		if result := fn.Fn(args...); result != nil {
 			return result
 		}
@@ -577,7 +577,7 @@ func applyFunction(fn object.Object, args []object.Object) object.Object {
 	}
 }
 
-func extendFunctionEnv(fn *object.Function, args []object.Object) *object.Environment {
+func extendFunctionEnv(fn object.Function, args []object.Object) *object.Environment {
 	env := object.NewEnclosedEnvironment(fn.Env)
 
 	for paramIdx, param := range fn.Parameters {

internal/evaluator/evaluator_test.go

@@ -354,7 +354,7 @@ func TestFunctionObject(t *testing.T) {
 	input := "fn(x) { x + 2; };"
 
 	evaluated := testEval(input)
-	fn, ok := evaluated.(*object.Function)
+	fn, ok := evaluated.(object.Function)
 	if !ok {
 		t.Fatalf("object is not Function. got=%T (%+v)", evaluated, evaluated)
 	}