[racket] [redex] side-condition matching upon errors

+1 for the debug annotation! it would be really helpful!

-- Éric


On Sep 4, 2013, at 3:04 PM, Robby Findler <robby at eecs.northwestern.edu> wrote:

> Just to be clear, the proposed change would affect only define-judgment-form, since that's the only place where side-condition is not implicitly unquoted.
> 
> But adding some kind of "debug" annotation that meant "if you get here, print something out" sounds actually quite useful.
> 
> Robby
> 
> 
> On Wed, Sep 4, 2013 at 1:50 PM, Jonathan Schuster <schuster at ccs.neu.edu> wrote:
> 
> As for backwards compatibility issues, I don't know how much people rely on side-condition taking something not-#f/#t... Probably too much :)
> (also, there could be a `side-condition-soft' variant that is not strict in the boolean-ness, or vice-versa)
> 
> 
> Well, if we're willing to force clients to change their code, then it isn't hard for them to write their own metafunctions that turn non-#f things into #ts.
> 
> But I think you're right that just changing this is a good idea and backwards compatibility be damned. I'll put it on my list.
> 
> There's at least one situation in which non-booleans in side conditions are important: debugging. Much of my Redex debugging involves adding code along the lines of "(side-condition (displayln (term <something>)))". Forcing booleans there would make that line even more verbose, and when it's being written a lot, that pain adds up.
> 
> I'd be in favor of something like side-condition-soft as described above. Or alternatively, it might make sense to have a "debug" clause that acts like printf, or even a "racket-expression" clause that evaluates the given racket expression, but does not affect the result of a metafunction the way side-condition does.
>