From: MonkeeSage <MonkeeSage@...>
Date: 2007-12-19T08:20:06+09:00
Subject: Re: Using 'when' as a statement modifier

On Dec 17, 10:31 pm, Tom Agnew <agne...@nospam.net> wrote:
> Hello all,
>
> I have a suggestion for an enhancement that could add to the readability
> of my programs.
>
> I'm a frequent user of 'if' and 'unless' statement modifiers.  It's a
> beautiful abbreviation that enhances the readability of my code.
>
> Here is a pattern that I use from time to time:
>
>         result = func(x) unless func(x)==y
>
> This has the potential to invoke func(x) twice in some implementations.
>
> It occurred to me that the 'case' semantics could be borrowed to create
> a useful new modifier.  Here's a suggestion that might be more efficient
> and possibly more readable:
>
>         result = func(x) when result==y

I'm not sure how easy it would be to implement or what other
drawbacks / benefits it might entail, but just for clarification, this
looks like it would be sugar for something like this (I'd never write
this, just trying to illustrate what I think is happening)...

result = tmp = func(x) == y ? tmp : nil; tmp = nil

> The modifier would act as a mini-continuation, so that the result would
> not be updated (i.e., it would be rolled back) if the condition is not
> satisfied.
>
> Then 'when' modifier could invoke the case equality operator by default.
>   For example:
>
>         result = func1(x) when 200..499
>         result = func2(x) when 500..999
>
> or even:
>
>         result = translate(x) when Class1,Class2
>         result = translate(x) when value1,range2,Class3
>
> Anyone else have a use for this?  Any thoughts??

In these examples (besides allowing multiple conditions), what would
be the difference between 'when' and 'if'?

> Best regards,
> Tom Agnew

Regards,
Jordan