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

31 Jul 2015

      #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)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by thomie):

 The message is now (ghc-7.10.2):

 {{{
 Prelude> print length

 <interactive>:2:1:
     No instance for (Show (t0 a0 -> Int))
       (maybe you haven't applied enough arguments to a function?)
       arising from a use of ‘print’
     In the expression: print length
     In an equation for ‘it’: it = print length
 }}}

 In commit bc2289e13d9586be087bd8136943dc35a0130c88:
 {{{
 Author: Mike Izbicki <>
 Date:   Wed Nov 19 18:29:37 2014 -0600

     ghc generates more user-friendly error messages

     Test Plan: Compiled ghc fine.  Opened ghci and fed it invalid code.
 It gave the improved error messages in response.

     Reviewers: austin

     Subscribers: thomie, simonpj, spacekitteh, rwbarton, simonmar, carter

     Differential Revision: https://phabricator.haskell.org/D201
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9613#comment:3
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