#10828: TH could do a better job of representing GADTs -------------------------------------+------------------------------------- Reporter: spinda | Owner: jstolarek Type: feature request | Status: new Priority: normal | Milestone: 8.0.1 Component: Template Haskell | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by jstolarek): * owner: => jstolarek Comment: I can work on implementing that, but I have one question:
I think, in light of comment:5, we should add proper GADT support in TH. Why "in light of comment:5"? I read through #10447 and I saw this example by Simon:
{{{#!hs data T1 a where MkT1 :: (a~Int) => a -> T1 a data T2 a where MkT2 :: Int -> T2 Int data T3 a where MkT3 :: (a~Int) => a -> T3 Int }}} All these declarations can be represented in TH: {{{#!hs data T1 a = a ~ Int => MkT1 a data T2 a = a ~ Int => MkT2 Int data T3 a = forall b. (a ~ Int, b ~ Int) => MkT3 b }}} It is possible to automatically derive `Foldable` for all three declarations `T1`, `T2` and `T3`, both in GADT form as well as in the standard form given above, so `DerivingFoldable` makes no distinction between these three declarations. Are there other declarations where `Foldable` distinguishes the two forms? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10828#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler