[GHC] #11112: Error message for accidentally using -> instead of =>

19 Nov 2015

      #11112: Error message for accidentally using -> instead of =>
-------------------------------------+-------------------------------------
           Reporter:  JulesBean      |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  7.10.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 Consider the following typo:

 {{{#!hs
 sort :: Ord s -> [s] -> [s]
 sort xs = Data.List.sort xs
 }}}

 GHC's error message in 7.10 is

 {{{
     Expected a type, but ‘Ord s’ has kind ‘GHC.Prim.Constraint’
     In the type signature for ‘Main.sort’:
       Main.sort :: Ord s -> [s] -> [s]
 }}}

 I would suggest that mentioning kinds and GHC.Prim.Constraint is a bit
 unfriendly in a vanilla session (with ConstraintKinds etc switched off).

 For comparison, the 6.12 error message was

 {{{
     Class `Ord' used as a type
     In the type signature for `sort': sort :: Ord a -> [a] -> [a]
 }}}

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11112
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