Fri Apr 9 11:44:20 PDT 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
View patch online:
http://darcs.haskell.org/cgi-bin/darcsweb.cgi?r=ghc;a=darcs_commitdiff;h=20100409184420-1287e-797ef851921f64e3563eae5626faa8836a8f315e.gz
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