[GHC] #9613: when giving an error "No instance for C (a -> b)", suggest that a function may be underapplied

19 Sep 2014

      #9613: when giving an error "No instance for C (a -> b)", suggest that a function
may be underapplied
-------------------------------------+-------------------------------------
       Reporter:  rwbarton           |                   Owner:
           Type:  feature request    |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler (Type     |                 Version:  7.8.3
  checker)                           |        Operating System:
       Keywords:                     |  Unknown/Multiple
   Architecture:  Unknown/Multiple   |         Type of failure:
     Difficulty:  Unknown            |  None/Unknown
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
 Suggestion of ibotty here:
 http://www.reddit.com/r/haskell/comments/2go92u/beginner_error_messages_in_c...

 {{{
 Prelude> print length

 <interactive>:2:1:
     No instance for (Show ([a0] -> Int)) arising from a use of ‘print’
         but there is an instance for (Show Int);
         maybe you omitted an argument to ‘length’ of type [a0]?
     In the expression: print length
     In an equation for ‘it’: it = print length
 }}}

 I guess the trickiest part will be figuring out what function is
 underapplied.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9613
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler