Re: Pattern synonym type flexibility

Think about it this way. The matching aspect of a pattern synonym is basically about defining a function to a somewhat weird type, except of course optimized and maybe a bit more general. data HList :: [*] -> * where HNil :: HList '[] HCons :: a -> HList as -> HList (a ': as) data

Re: Pattern synonym type flexibility

I don't know what that means. There's no way to enforce duality at the term level. Enforcing it at the type level prevents me from doing what I want and serves no apparent purpose. Remember that pattern synonyms are all about providing nice syntax, not adding essential expressiveness. On Apr 20,

Re: Pattern synonym type flexibility

Shouldn't the design simply be both directions are the dual of the other, and pure in some sense ? On Wednesday, April 20, 2016, David Feuer wrote: > To some degree, it probably could be. But I believe that imposing any > substantial relationship between the smart

Re: Pattern synonym type flexibility

To some degree, it probably could be. But I believe that imposing any substantial relationship between the smart constructor and the pattern synonym is likely to fall squarely into the category of things that are subtle, hard, and almost completely useless. In the arrangement I suggested, people

Re: Pattern synonym type flexibility

Would that duality be related to the given vs wanted constraints ? On Wednesday, April 20, 2016, David Feuer wrote: > As far as I can tell from the 7.10 documentation, it's impossible to > make a bidirectional pattern synonym used as a constructor have a > different type

Pattern synonym type flexibility

As far as I can tell from the 7.10 documentation, it's impossible to make a bidirectional pattern synonym used as a constructor have a different type signature than when used as a pattern. Has this been improved in 8.0? I really want something like class FastCons x xs | xs -> x where fcons :: x