[GHC] #11243: Use Type Synonyms to Compress Errors

[GHC]

#11243: Use Type Synonyms to Compress Errors
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        Reporter:  crockeea          |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by rwbarton):

 So the large types appear in the known constraints and the types of things
 in scope, like
 {{{
 examples/Main.hs:113:23:
     Could not deduce (Typeable (* -> *) sym0)
       arising from a use of ‘genKeys’
     from the context [LARGE]
       bound by the inferred type of
                prfTest :: [LARGE]
       at examples/Main.hs:(104,1)-(123,18)
     The type variable ‘sym0’ is ambiguous
     Relevant bindings include
       ast0 :: [LARGE]
         (bound at examples/Main.hs:110:3)
     In the first argument of ‘evalCryptoRandIO’, namely
       ‘(genKeys v ast0)’
     In the second argument of ‘(=<<)’, namely
       ‘evalCryptoRandIO (genKeys v ast0)’
     In a stmt of a 'do' block:
       (ast1, idMap) <- time "Generating keys: "
                        =<< evalCryptoRandIO (genKeys v ast0)
 }}}

 I think this isn't what changed in HEAD; that was when the error actually
 involved a disagreement between types which were expressed using type
 synonyms.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11243#comment:4>
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