#3877: Require XOverlappingInstances for the most specific instance only
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Reporter: traz161616 | Owner: igloo
Type: feature request | Status: new
Priority: normal | Milestone: 7.2.1
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 simonpj):
* owner: => igloo
Comment:
OK done:
{{{
Tue Dec 14 10:05:00 PST 2010 [email protected]
* Instance declaration overlap allowed if *either* has
-XOverlappingInstances
This satisfies Trac #3877. Documentation is changed too.
I'm not sure if this should go in 7.0.2.
M ./compiler/types/InstEnv.lhs -8 +12
M ./docs/users_guide/glasgow_exts.xml -19 +10
}}}
I'm agnostic about whether this should sneak into 7.0.2 (even if there is
time to do so). It allows more programs to compile (like a bug fix), but
it'd mean that any program relying on it would have to depend on 7.0.2 and
not 7.0.1 etc.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3877#comment:13>
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The Glasgow Haskell Compiler
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