[GHC] #9913: Discrepancy in type synonym definition and usage

20 Dec 2014


      #9913: Discrepancy in type synonym definition and usage
-------------------------------------+-------------------------------------
       Reporter:  Iceland_jack       |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  lowest             |               Milestone:
      Component:  Compiler (Parser)  |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  x86                |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:  GHC
     Blocked By:                     |  rejects valid program
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Minor consistency issue, the following compiles fine (note parentheses):

 {{{#!hs
 type Alg f a = f a -> a

 initial :: Alg(f) a
 initial = undefined
 }}}

 But changing the definition to mirror its use:

 {{{#!hs
 type Alg(f) a = f a -> a

 initial :: Alg(f) a
 initial = undefined
 }}}

 and it fails with:

 {{{#!hs
     Unexpected type ‘f’
     In the type declaration for ‘Alg’
     A type declaration should have form
       type Alg a b c = ...
 Failed, modules loaded: none.
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9913
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