[GHC] #11712: Very confusing error message with -fprint-explicit-kinds

[GHC]

#11712: Very confusing error message with -fprint-explicit-kinds
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by bgamari:

@@ -11,1 +11,3 @@
- the second it is applied to three.
+ the second it is applied to three. Presuambly this is due to the former
+ being kind heterogeneous, so at very least I'd think that `~~` should be
+ used here.

New description:

 While trying to work out a type error I encountered the following,

 {{{
 compiler/utils/Binary.hs:607:59: error:
     • Could not deduce: (~) * * arg *
       from the context: (~) * k (arg -> res)
     ...
 }}}

 Note how in the first line `(~)` is applied to four arguments whereas on
 the second it is applied to three. Presuambly this is due to the former
 being kind heterogeneous, so at very least I'd think that `~~` should be
 used here.

 In general, it would be nice if we could make equalities a bit more
 readable, perhaps special-casing them in the pretty-printer as,
 {{{
 (a :: k) ~ (b :: k')
 }}}

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11712#comment:1>
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