further improvements

internal/object/int.go

@@ -27,17 +27,21 @@ func (i Integer) String() string {
 }
 
 func (i Integer) Add(other Object) (Object, error) {
-	if !AssertTypes(other, IntegerType) {
+	switch obj := other.(type) {
+	case Integer:
+		return Integer{i.Value + obj.Value}, nil
+	default:
 		return nil, NewBinaryOpError(i, other, "+")
 	}
-	return Integer{i.Value + other.(Integer).Value}, nil
 }
 
 func (i Integer) Sub(other Object) (Object, error) {
-	if !AssertTypes(other, IntegerType) {
+	switch obj := other.(type) {
+	case Integer:
+		return Integer{i.Value - obj.Value}, nil
+	default:
 		return nil, NewBinaryOpError(i, other, "-")
 	}
-	return Integer{i.Value - other.(Integer).Value}, nil
 }
 
 func (i Integer) Mul(other Object) (Object, error) {
@@ -115,15 +119,16 @@ func (i Integer) Negate() Object {
 }
 
 func (i Integer) Compare(other Object) int {
-	if obj, ok := other.(Integer); ok {
-		switch {
-		case i.Value < obj.Value:
+	switch obj := other.(type) {
+	case Integer:
+		if i.Value < obj.Value {
 			return -1
-		case i.Value > obj.Value:
-			return 1
-		default:
-			return 0
 		}
+		if i.Value > obj.Value {
+			return 1
+		}
+		return 0
+	default:
+		return -1
 	}
-	return -1
 }