Hi Merijn, Let me suggest the Fail type family in http://www.haskell.org/pipermail/haskell-cafe/2013-November/111549.html
-- Adam On Tue, Jan 14, 2014 at 8:56 AM, Merijn Verstraaten <mer...@inconsistent.nl> wrote: > I was trying to fix one of my closed type families examples for the new > syntax, and run into an unfortunate issue. Due to a kind error in my code one > of my constraints was being silently discarded (see ticket: > https://ghc.haskell.org/trac/ghc/ticket/8669) > > The main reason I resorted to this (in hindsight) ill-kinded hack is the lack > of a vacuous (i.e. never holding) constraint to produce type errors. I would > love to be able to explicitly force GHC into realising "this constraint can > never hold", if I had the ability to pass along a String/Symbol to be > reported to the user, that would be even better. > > Cheers, > Merijn > > _______________________________________________ > Glasgow-haskell-users mailing list > Glasgow-haskell-users@haskell.org > http://www.haskell.org/mailman/listinfo/glasgow-haskell-users > _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
