#3965: 'deriving Data' compilation regression 6.10.1 -> 6.12.1
-------------------------+--------------------------------------------------
Reporter: ronwalf | Owner:
Type: bug | Status: merge
Priority: high | Milestone: 6.12.3
Component: Compiler | Version: 6.12.1
Keywords: | Difficulty:
Os: MacOS X | Testcase: deriving/should_compile/T3965
Architecture: x86 | Failure: GHC rejects valid program
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Changes (by simonpj):
* status: new => merge
* testcase: => deriving/should_compile/T3965
Comment:
Great report, thanks. Fixed by
{{{
Fri Apr 9 19:44:20 BST 2010 [email protected]
* Fix Trac #3965: tighten conditions when deriving Data
It's tricky to set up the context for a Data instance. I got it wrong
once, and fixed it -- hence the "extra_constraints" in
TcDeriv.inferConstraints.
But it still wasn't right! The tricky bit is that dataCast1 is only
generated when T :: *->*, and dataCast2 when T :: *->*->*. (See
the code in TcGenDeriv for dataCastX.
M ./compiler/typecheck/TcDeriv.lhs -8 +14
}}}
Perhaps merge to 6.12.3
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3965#comment:4>
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