new function isRational() that return true is the passed value is integere or fraction

utils.go

@@ -44,6 +44,13 @@ func IsFract(v any) (ok bool) {
 	return ok
 }
 
+func IsRational(v any) (ok bool) {
+	if _, ok = v.(*fraction); !ok {
+		_, ok = v.(int64)
+	}
+	return ok
+}
+
 func IsNumber(v any) (ok bool) {
 	return IsFloat(v) || IsInteger(v)
 }