#3714: Improve error message if an associated family declaration has excess
parameters
---------------------------+------------------------------------------------
Reporter: simonpj | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 6.10.4
Resolution: | Keywords:
Difficulty: | Os: Unknown/Multiple
Testcase: | Architecture: Unknown/Multiple
Failure: None/Unknown |
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Comment (by MartijnVanSteenbergen):
Yes, I do intend to never use specific types for {{{e}}} when writing
instances. In every instance it will be a 'polymorphic' {{{e}}} (if
polymorphic is the right word here), so it behaves like argument, not an
index (using Simon's terms). I'm sorry I haven't been able to make myself
clear sooner. :-) The idea behind the bang solution is exactly what I have
in mind.
Part of the confusion I think is that I was already expecting this to
work: the problem only occurs inside type classes and instances, and the
compiler knows exactly where the bangs should go, namely those
indices/parameters on the left of the {{{::}}} that do not appear in the
type class header.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3714#comment:5>
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