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

[GHC]

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

 the underapplied function is
 {{{
 length . head . tail
 }}}

 it is missing an argument of type {{{[[a0]]}}}.

 am i missing things?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9613#comment:2>
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