[GHC] #8634: Code valid in GHC 7.6 is impossible to move over GHC 7.7 (because of liberal coverage condition)
GHC
ghc-devs at haskell.org
Fri Dec 27 19:22:38 UTC 2013
#8634: Code valid in GHC 7.6 is impossible to move over GHC 7.7 (because of
liberal coverage condition)
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Reporter: danilo2 | Owner:
Type: bug | Status: new
Priority: high | Milestone:
Component: Compiler | Version: 7.7
Resolution: | Keywords:
Operating System: | Architecture: Unknown/Multiple
Unknown/Multiple | Difficulty: Unknown
Type of failure: None/Unknown | Blocked By:
Test Case: | Related Tickets: #1241, #2247, #8356
Blocking: |
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Comment (by rwbarton):
> Unfortunatelly I can not :( Look, Vector_testid indicates, that it holds
"testid" method (it should be named Vector_method1 instead - sorry for
that typo.
> If we get more associated functions, we would have Vector_method2,
Vector_method3 etc, so we need to distinguish them - see the sample code
in this comment.
That doesn't seem to be a problem, as those will be instances of different
classes `Method2`, `Method3`.
{{{#!haskell
instance (m ~ Vector_method1, out ~ (t1->t1)) => Method1 (Vector a) m out
where
method1 = (Vector_method1 . testid)
instance (m ~ Vector_method2, out ~ (t1->(t1,t1))) => Method2 (Vector a) m
out where
method2 = (Vector_method2 . testf2)
}}}
With these changes your second program runs for me with GHC HEAD as long
as I comment out `testx`--which is not used in the program.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8634#comment:4>
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