From: "David A. Black" <dblack@...>
Date: 2008-05-25T19:55:43+09:00
Subject: Re: lambda, ->, haskell, and so on

Hi --

On Sun, 25 May 2008, Phlip wrote:

>>     assert_yin_yang -> { q +=  0 }, 'it broke!', -> { q == 42 }
>
> Props! I was hoping that's what -> was for!
>
> About _{}, I meant making a global identifier out of _ was dangerous. Of 
> course we sometimes use it as a private identifier, in a Prolog kinda way, 
> such as |a,_,c|, to identify a variable we don't want anyone to access. My 
> library should not collide with anyone doing that, so I did not put _{} in 
> it; it's just a recommendation in the documentation.

My advice, in passing, would be not to recommend it. As you say, _ is
usually used (though I don't tend to use it myself) as a throwaway,
precisely because it's non-communicative. So having it do something
where someone looking at the code might actually want to know what
it's doing is probably not ideal.

> The "in the way" alternative was:
>
>  assert_yin_yang proc{ q +=  0 }, 'it broke!',
>                  proc{ q == 42 }
>
> That sorta obviates my standard advertizing jingle - more assert bang for 
> less coding buck! 'proc' ain't DRY there...

I don't think I'd describe those two 'proc's as a case of repeating
yourself, since each of them is serving the minimal purpose that
'proc' can serve. Or, to put it another way, proc { q == 42 } is in no
way a repetition of proc { q += 0 }.


David

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