#9981: Potential typechecker regression in GHC 7.10.1RC -------------------------------------+------------------------------------- Reporter: hvr | Owner: simonpj Type: bug | Status: new Priority: highest | Milestone: 7.10.1 Component: Compiler | Version: 7.10.1-rc1 (Type checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: GHC rejects Architecture: | valid program Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- The following snippet (extracted from hackage:index-core) is accepted by GHCs prior to GHC 7.10: {{{#!hs {-# LANGUAGE Rank2Types, TypeOperators #-} module Foo where type a :-> b = forall i . a i -> b i class IFunctor f where fmapI :: (a :-> b) -> (f a :-> f b) class (IFunctor m) => IMonad m where returnI :: a :-> m a bindI :: (a :-> m b) -> (m a :-> m b) (?>=) :: (IMonad m) => m a i -> (a :-> m b) -> m b i (?>=) = flip bindI }}} {{{ $ ghci-7.8.4 -Wall Foo.hs GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Control.IMonad.Core ( Foo.hs, interpreted ) Ok, modules loaded: Control.IMonad.Core. λ:2> :browse type (:->) (a :: * -> *) (b :: * -> *) = forall i. a i -> b i class IFunctor (f :: (* -> *) -> * -> *) where fmapI :: (a :-> b) -> f a :-> f b class IFunctor m => IMonad (m :: (* -> *) -> * -> *) where returnI :: a i -> m a i bindI :: (a :-> m b) -> m a :-> m b (?>=) :: IMonad m => m a i -> (a :-> m b) -> m b i }}} vs. {{{ $ ghci-7.10.0.20141227 -Wall Foo.hs GHCi, version 7.10.0.20141227: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Control.IMonad.Core ( Foo.hs, interpreted ) Foo.hs:15:14: Couldn't match type ‘a i0 -> m b i0’ with ‘forall i1. a i1 -> m b i1’ Expected type: (a i0 -> m b i0) -> m a i -> m b i Actual type: a :-> m b -> m a i -> m b i Relevant bindings include (?>=) :: m a i -> a :-> m b -> m b i (bound at Foo.hs:15:1) In the first argument of ‘flip’, namely ‘bindI’ In the expression: flip bindI Failed, modules loaded: none. λ:2> }}} I'm not sure though whether that module was valid to begin with... -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9981 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler