#10405: Pattern synonym fails with (Exp Bool) but works with (t ~ Bool => Exp t) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.1-rc1 checker) | Keywords: Resolution: invalid | Architecture: x86 Operating System: Linux | Test Case: Type of failure: GHC rejects | Blocking: valid program | Differential Revisions: Blocked By: | Related Tickets: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Egg on my face, I should have realised that. Thanks for the response. For anyone in a similar situation and for future evaluation of #9953 I have the expression: {{{#!haskell data Tag a where TInt :: Tag Int TBool :: Tag Bool … data Exp a where Fn₁ :: String -> Tag a -> (a -> b) -> (Exp a -> Exp b) Fn₂ :: String -> Tag a -> Tag b -> (a -> b -> c) -> (Exp a -> Exp b -> Exp c) … }}} To be able to match against expressions of type `Exp a` I needed to add an additional tag for the return type: {{{#!haskell data Exp a where Fn₁ :: String -> Tag a -> Tag b -> (a -> b) -> (Exp a -> Exp b) Fn₂ :: String -> Tag a -> Tag b -> Tag c -> (a -> b -> c) -> (Exp a -> Exp b -> Exp c) … }}} {{{#!haskell pattern Leq :: (a ~ Int, b ~ Int, c ~ Bool) => Exp a -> Exp b -> Exp c pattern Leq a b ← Fn₂ "leq" TInt TInt TBool _ a b where Leq a b = Fn₂ "leq" TInt TInt TBool (<=) a b }}} is the final version. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10405#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler