[GHC] #9173: Better type error messages

[GHC]

#9173: Better type error messages
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        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.8.2
      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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Comment (by chreekat):

 Replying to [comment:20 sgillespie]:
 > I'd like to have a look. What is the proposed message? Should we use the
 original message below?
 >
 > {{{
 > Foo.hs:2:20
 >   inferred: "Just 5" has type "Maybe a0"
 >   expected: second argument of "($)" must have type "Int"
 >   in the expression: addThree $ Just 5
 > }}}

 I vote for the simpler wording change rather than whatever acrobatics
 would be required to overcome the problems listed here:
 https://mail.haskell.org/pipermail/ghc-devs/2015-August/009559.html

 I guess that the patch mentioned above makes those bigger changes
 possible, but still.

 For the wording change, I think adding "...from context" is universally
 desired. See my comment:14, and the one following it, for suggested text.

 Incidentally, I dislike the eldest proposal (quoted in this comment)
 because it splits the necessary information over a couple lines, which is
 not so nice for integrating with vim's `:make` command. ;)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9173#comment:21>
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