#3877: Require XOverlappingInstances for the most specific instance only
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Reporter: traz161616 | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: 7.0.1
Component: Compiler (Type checker) | Version: 6.12.1
Resolution: | Keywords: XOverlappingInstances
Testcase: | Blockedby:
Difficulty: | Os: Unknown/Multiple
Blocking: | Architecture: Unknown/Multiple
Failure: GHC rejects valid program |
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Changes (by gidyn):
* status: closed => new
* cc: gid...@… (added)
* os: Linux => Unknown/Multiple
* architecture: x86_64 (amd64) => Unknown/Multiple
* resolution: wontfix =>
Comment:
I've just been his by this, and it's exceedingly annoying; we are
prevented from writing custom Show instances for type synonyms.
I've changed the title to request this change, as described in the
documentation.(Perhaps the rule should instead say that the overlapping
instance declaration should be compiled in this way, rather than the
overlapped one ... We are interested to receive feedback on these points.)
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3877#comment:4>
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