[GHC] #12928: Too easy to trigger CUSK condition using TH

[GHC]

#12928: Too easy to trigger CUSK condition using TH
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        Reporter:  int-index         |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  high              |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 >  How come we don't have a notion of "complete user-supplied type" to
 support polymorphic recursion at term level and still retain type
 inference?

 We do!  It's called a type signature.

 An alternative to the CUSK thing would be to provide for kind siguatures;
 e.g.
 {{{
 type D :: (* -> *) -> *
 type D f = f Int
 }}}
 We didn't do that because at the time it seemed more syntactically
 invasive.  But it'd make it all much clearer.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12928#comment:3>
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