[GHC] #10794: Extension request: "where" clauses in type signatures

[GHC]

#10794: Extension request: "where" clauses in type signatures
-------------------------------------+-------------------------------------
        Reporter:  danso             |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  lowest            |               Milestone:
       Component:  Compiler (Type    |                 Version:  7.10.2
  checker)                           |
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by nomeata):

 {{{#!hs
 fold :: f -> [a] -> a
         where f :: a -> a -> a
 }}}
 is certainly confusing, because in the first line `f` is used like a type,
 but in the second, `f` is used like a value (or `a -> a -> a` is used like
 a kind

 Maybe you meant
 {{{#!hs
 fold :: f -> [a] -> a
         where f = a -> a -> a
 }}}
 which could be extended to allow

 {{{#!hs
 fold :: f -> [a] -> a
         where f :: *
               f = a -> a -> a
 }}}

 I’m sure the type level programming wizards and dependently typed
 programmers will have the greatest need for such an extension, and have a
 good opinion here.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10794#comment:1>
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