Right, so I need a separate metafunction for each pattern I want to negate.

On Mon, Oct 24, 2016 at 6:56 PM, Robby Findler <ro...@eecs.northwestern.edu>
wrote:

> I am saying to write this:
>
> (define-metafunction L
>   [(not-thing pat) #false]
>   [(not-thing any) #true])
>
> and then where you wrote:
>
>   (where/not pat tm)
>
> write this:
>
>   (where #true (not-thing pat))
>
>
>
> On Mon, Oct 24, 2016 at 5:47 PM, Sam Caldwell <s...@ccs.neu.edu> wrote:
> >> In the meantime, consider using a metafunction with an `else` clause.
> >
> > This would entail fixing the pattern, right? As in, I can write a
> > metafunction deciding whether a term does not match a pattern, but I
> can't
> > write a metafunction taking both the term and the pattern.
> >
> > I'm ok with failed matches not being first-class in Redex, but I'm a
> little
> > disappointed if I can't create my own shorthand.
> >
> > Thanks,
> > Sam Caldwell
> >
> > On Mon, Oct 24, 2016 at 6:31 PM, Robby Findler <
> ro...@eecs.northwestern.edu>
> > wrote:
> >>
> >> Unfortunately, Redex's pattern language does not currently support
> >> `not`. It might be easy to add it, or maybe hard, or maybe impossible.
> >> Offhand, it seems probably possible to support in the unifier and
> >> impossible in the enumerator and not hard in the matcher.
> >>
> >> In the meantime, consider using a metafunction with an `else` clause.
> >>
> >> Robby
> >>
> >>
> >> On Mon, Oct 24, 2016 at 5:15 PM, Sam Caldwell <s...@ccs.neu.edu> wrote:
> >> > I have a Redex judgment that I would like to specify in terms of a
> >> > *failed*
> >> > pattern match. I can write this like so:
> >> >
> >> > [(side-condition ,(not (redex-match? L pat (term tm)))
> >> > ------------------------------------------------------------------
> >> > ...]
> >> >
> >> > which works, but I would rather just abbreviate this using a macro
> >> > (since
> >> > afaict there are no existing constructs in redex to do this), so I
> could
> >> > write for instance:
> >> >
> >> > [(where/not pat tm)
> >> > --------------------------
> >> > ...]
> >> >
> >> > But then I get an error: "define-judgment-form: expected judgment form
> >> > name
> >> > in: where/not"
> >> >
> >> > Does anybody know how to achieve this?
> >> >
> >> > Thanks,
> >> > Sam Caldwell
> >> >
> >> > Full example:
> >> >
> >> > ==============================================================
> >> >
> >> > #lang racket
> >> >
> >> > (require redex)
> >> >
> >> > (define-language L
> >> >   (E number (+ E E)))
> >> >
> >> > (define-syntax (where/not stx)
> >> >   (syntax-case stx ()
> >> >     [(_ pat tm)
> >> >      #'(side-condition ,(not (redex-match? L pat (term tm))))]))
> >> >
> >> > (define-judgment-form L
> >> >   #:mode (j I)
> >> >   [(where/not number E)
> >> >    ---------------------
> >> >    (j E)])
> >> >
> >> > --
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> >
>
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