Re: [GHC] #14643: Partial type signatures interact unexpectedly with :browse (was: Partial type signatures in spliced TH declarations behave unexpectedly)

7 Jan 2018

      #14643: Partial type signatures interact unexpectedly with :browse
-------------------------------------+-------------------------------------
        Reporter:  mnislaih          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      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:                    |
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Comment (by RyanGlScott):

 Note that this has nothing to do with Template Haskell. You can also
 trigger the issue with this (slightly more) minimal file:

 {{{#!hs
 {-# LANGUAGE PartialTypeSignatures #-}
 {-# LANGUAGE TemplateHaskell #-}
 module Bug where

 f :: (Monad m, _) => [m a] -> m [a]
 f' :: (Monad m, _) => [m a] -> m [a]
 f = f'
 f' [] = return []
 f' (x:xx) = f xx

 g, g' :: (Monad m, _) => [m a] -> m [a]
 g = g'
 g' [] = return []
 g' (x:xx) = g xx
 }}}

 {{{
 $ ghci Bug.hs -Wno-partial-type-signatures
 GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 Ok, one module loaded.
 λ> :browse
 f :: (Monad m, Monad m) => [m a] -> m [a]
 f' :: (Monad m, Monad m) => [m a] -> m [a]
 g ::
   (Monad GHC.Types.Any, Monad m) =>
   [GHC.Types.Any GHC.Types.Any] -> GHC.Types.Any [GHC.Types.Any]
 g' :: (Monad GHC.Types.Any, Monad m) => [m a] -> m [a]
 }}}

 The same behavior also happens with `:type v` (but not `:type`, since that
 performs deep instantiation of the types):

 {{{
 λ> :type +v f
 f :: (Monad m, Monad m) => [m a] -> m [a]
 λ> :type +v f'
 f' :: (Monad m, Monad m) => [m a] -> m [a]
 λ> :type +v g
 g :: (Monad GHC.Types.Any, Monad m) =>
      [GHC.Types.Any GHC.Types.Any] -> GHC.Types.Any [GHC.Types.Any]
 λ> :type +v g'
 g' :: (Monad GHC.Types.Any, Monad m) => [m a] -> m [a]
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14643#comment:2
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