#15645: TypeChecking of Monad patterns incorrect with RebindableSyntax and OverloadedStrings -------------------------------------+------------------------------------- Reporter: NeilMitchell | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by NeilMitchell): The use case is for `Prelude` replacement modules that seek to switch the type of `[Char]` to something like `Text`. A standard way is to define your own `Monad`/`MonadFail` class which has `fail :: Text -> m a` in it. If that class is forced to have `fail :: [Char] -> m a` instead (as it is now) then all your users have to implement a function working on `[Char]`, even though for everything else in your custom library, they never see `[Char]` and your custom `Prelude` has no other `[Char]` related functions. In the particular example I'm working on, the `Char` type has been eliminated entirely, aside from the `fail` function. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15645#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler