[racket] (where-not ...) in Redex

I would almost prefer the use of 'when' for 'where' and the introduction of 'unless'. 

The type setting of 'when' could still use 'where' as the English word (and perhaps we can have a way to override it). 

I am not sure how to type set 'unless' other than by providing a the negative operator as an argument != 

-- Matthias




On Aug 22, 2012, at 3:47 PM, Asumu Takikawa wrote:

> Hi all,
> 
> Had a question/feature request for Redex. In various models, I've
> encountered situations where I wanted the dual behavior to the
> (where pattern term) clause of Redex (i.e., does term *not* match this
> pattern).
> 
> In the past, I've used side-conditions or where clauses with predicate
> metafunctions for this case. For example,
>  (side-condition ,(not (redex-match ...)))
> 
>  or
> 
>  (where #f (matches this that))
> 
> Both of these have the disadvantage that it's more work to typeset.
> It would be convenient to have a form like
>  (where-not pattern term)
> 
> that would typeset like the following:
> 
>  where term ≠ pattern
> 
> This seems like a common enough pattern that it would be nice to support
> it as a built-in (and typeset) construct. Does that seem like a
> reasonable thing to add?
> 
> Cheers,
> Asumu
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users

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