type checking and error handling for builtins improved.

builtins/max.go

@@ -2,28 +2,30 @@ package builtins
 
 import (
 	"monkey/object"
+	"monkey/typing"
 	"sort"
 )
 
 // Max ...
 func Max(args ...object.Object) object.Object {
-	if len(args) != 1 {
-		return newError("wrong number of arguments. got=%d, want=1",
-			len(args))
+	if err := typing.Check(
+		"max", args,
+		typing.ExactArgs(1),
+		typing.WithTypes(object.ARRAY_OBJ),
+	); err != nil {
+		return newError(err.Error())
 	}
 
-	if a, ok := args[0].(*object.Array); ok {
-		// TODO: Make this more generic
-		xs := make([]int, len(a.Elements))
-		for n, e := range a.Elements {
-			if i, ok := e.(*object.Integer); ok {
-				xs = append(xs, int(i.Value))
-			} else {
-				return newError("item #%d  not an `int` got=%s", n, e.Type())
-			}
+	a := args[0].(*object.Array)
+	// TODO: Make this more generic
+	xs := make([]int, len(a.Elements))
+	for n, e := range a.Elements {
+		if i, ok := e.(*object.Integer); ok {
+			xs = append(xs, int(i.Value))
+		} else {
+			return newError("item #%d  not an `int` got=%s", n, e.Type())
 		}
-		sort.Ints(xs)
-		return &object.Integer{Value: int64(xs[len(xs)-1])}
 	}
-	return newError("argument #1 to `max` expected to be `array` got=%T", args[0].Type())
+	sort.Ints(xs)
+	return &object.Integer{Value: int64(xs[len(xs)-1])}
 }