On Tue, Oct 14, 2014 at 10:26:46PM +0200, S. Doaitse Swierstra wrote:
> The GHC manual already for quite a number of version states:
>
> • Arrow notation (see Section 7.17, “Arrow notation ”) uses whatever
> arr, (>>>), first, app, (|||) and loop functions are in scope.
> But unlike the other constructs, the types of these functions must
> match the Prelude types very closely. Details are in flux; if you want to use
> this, ask!
>
> When using this feature we get the error:
>
> "Var/Type length mismatch:
> [s{tv aVL} [tv]]
> []
> ghc: panic! (the 'impossible' happened)
> (GHC version 7.8.3 for x86_64-apple-darwin):
> tcTyVarDetails s{tv aVL} [tv]
>
> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug";
>
> So our question is whether we should really report this as a bug, and/or what
> we can do about this.
It already has a bug entry: #7828. What would help is to know the kind
of use you have in mind, to see whether it fits with the proposed solution.
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