[GHC] #8560: undeducable Typeable error with data kinds when deriving Data for GADT in GHC version 7.7.20131122
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Mon Nov 25 17:14:04 UTC 2013
#8560: undeducable Typeable error with data kinds when deriving Data for GADT in
GHC version 7.7.20131122
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Reporter: carter | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.7
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture: Unknown/Multiple
Type of failure: None/Unknown | Difficulty: Unknown
Test Case: | Blocked By:
Blocking: | Related Tickets:
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Comment (by simonpj):
I have not even begun to think what `deriving( Data )` might do for GADTs.
At Lennart's request, we did make "standalone deriving" simply generate
code, and if it doesn't typecheck it's your problem. See
[http://www.haskell.org/ghc/docs/latest/html/users_guide/deriving.html
#stand-alone-deriving the manual] (fourth bullet). See #3102, and #3702
for someone who liked it.
I'm not sure that was a good decision, especially for jolly complicated
classes like `Data`.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8560#comment:4>
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