#12652: Type checker no longer accepting code using function composition and rank-n types -------------------------------------+------------------------------------- Reporter: ezyang | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler (Type | Version: 8.1 checker) | 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: | -------------------------------------+------------------------------------- Comment (by simonpj): Richard is right on all counts. This works {{{ h = (.) @(M ()) @(M ()) @Int f g }}} recalling that `(.)` has type {{{ (.) :: forall b c a. (b -> c) -> (a -> b) -> a -> c -- Defined in ‘GHC.Base’ }}} It seems to me that if a special case for `($)` is justified, then having one for `(.)` as well would make sense. Perhaps using it should require `-XImpredicativeTypes` though? Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12652#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler