Fixity of field-deconstructors incorrect

The example below

module Foo where

data SomeException

newtype ContT r m a = ContT {runContT :: (a -> m r) -> m r}

runContT' :: ContT r m a -> (a -> m r) -> m r
runContT' = runContT

catch_ :: IO a -> (SomeException -> IO a) -> IO a
catch_ = undefined

-- has type error
foo :: IO ()
foo = (undefined :: ContT () IO a) `runContT` (undefined :: a -> IO ()) `catch_` (undefined :: SomeException -> IO ()) 

-- typechecks
foo' :: IO ()
foo' = (undefined :: ContT () IO a) `runContT'` (undefined :: a -> IO ()) `catch_` (undefined :: SomeException -> IO ())

works with GHC 7.10 but breaks with GHC HEAD currently with:

foo.hs:15:47: error:
    • Couldn't match expected type ‘a0 -> IO ()’
                  with actual type ‘IO ()’
    • In the second argument of ‘runContT’, namely
        ‘(undefined :: a -> IO ())
         `catch_` (undefined :: SomeException -> IO ())’
      In the expression:
        runContT
          (undefined :: ContT () IO a)
          (undefined :: a -> IO ())
          `catch_` (undefined :: SomeException -> IO ())
      In an equation for ‘foo’:
          foo
            = runContT
                (undefined :: ContT () IO a)
                (undefined :: a -> IO ())
                `catch_` (undefined :: SomeException -> IO ())

foo.hs:15:48: error:
    • Couldn't match expected type ‘IO ()’
                  with actual type ‘a1 -> IO ()’
    • In the first argument of ‘catch_’, namely
        ‘(undefined :: a -> IO ())’
      In the second argument of ‘runContT’, namely
        ‘(undefined :: a -> IO ())
         `catch_` (undefined :: SomeException -> IO ())’
      In the expression:
        runContT
          (undefined :: ContT () IO a)
          (undefined :: a -> IO ())
          `catch_` (undefined :: SomeException -> IO ())

Trac metadata

Trac field	Value
Version	7.10.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture