Is there a way to safely redeclare a symbol?

Question

I often find myself experimenting in the REPL and I will say something like:

subset Bar of Int where * %% 57;

Then I play around with checks on the Bar-ness for things for a bit.

Everything is happy, until I realize that I want to change the definition of Bar.

If I just redefine Bar, I get a Redeclaration of symbol exception.

I tried using MONKEY-TYPING and augment like this:

use MONKEY-TYPING;
augment subset Bar of Int where * %% 37;

But that netted me the same error.

Why do I want this? So I can iterate on my subset (or class, or other symbol) definitions, while reusing the tests I've already typed that are in my history.

Answer 1

该REPL有它的缺点。它是EVAL试图协同工作的语句的精心构建。有时那行不通。

我想我们能做的最好的就是引入REPL命令，该命令会使它忘记以前所做的一切。欢迎补丁！:-)

Answer 2

我认为 REPL 的部分魔力是通过EVAL将每个新输入放入新的嵌套词法范围中来实现的。因此，如果您使用mythen 声明事物，则可以使用稍后输入的声明来隐藏它们：

my subset Bar of Int where * %% 57;
sub take-Bar(Bar $n) { say "$n is Bar" }
take-Bar 57;

my subset Bar of Int where * %% 42;
sub take-Bar(Bar $n) { say "$n is Bar" }
take-Bar 42;

如果省略my，则将使用forsubset和class声明，因为实际上是+ 将符号添加到封闭包中...；事实证明，如果您从包中删除该符号，您可以稍后再次隐藏它：ourourmy

subset Bar of Int where * %% 57;
GLOBAL::<Bar>:delete;
subset Bar of Int where * %% 42;
42 ~~ Bar;

注意：这些结果仅来自我在 REPL 中的实验。我不确定是否还有其他未知的副作用。