util files moved form kern to util package

kern/function.go

@@ -14,6 +14,11 @@ type FuncTemplate func(ctx ExprContext, name string, args map[string]any) (resul
 
 type DeepFuncTemplate func(a, b any) (eq bool, err error)
 
+func IsFunctor(v any) (ok bool) {
+	_, ok = v.(Functor)
+	return
+}
+
 // ---- Common functor definition
 type BaseFunctor struct {
 	info ExprFunc