#6002: GHC 7.4+ thinks class instance is incoherent, 7.0.4 disagrees
---------------------------------+------------------------------------------
Reporter: heisenbug | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
---------------------------------+------------------------------------------
Comment(by simonpj):
Reminder: I said "I was going to say that a workaround is to use
`-XIncoherentInstances`; but in fact that does not currently work,
although it should. I'll fix that part."
I don't know why 7.0.4 accepted it. But HEAD's rejection is for a good
reason, as I explain above.
Nothing to do with phantom types; the issue here, as I say above, is what
the type-function application `(Plus a1 a2)` might evaluate to.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6002#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
