#4528: stand-alone deriving sometimes fails for GADTs
------------------------------------------+---------------------------------
Reporter: nestra | Owner:
Type: bug | Status: merge
Priority: normal | Milestone:
Component: Compiler (Type checker) | Version: 7.0.1
Keywords: deriving mechanism, GADTs | Testcase:
deriving/should_fail/T4528, deriving/should_run/T4528a
Blockedby: | Difficulty:
Os: Linux | Blocking:
Architecture: x86_64 (amd64) | Failure: Compile-time
performance bug
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Changes (by simonpj):
* status: new => merge
* testcase: => deriving/should_fail/T4528, deriving/should_run/T4528a
Comment:
OK two patches. This one tightens up the defn of what can be
enumerations.
{{{
Wed Dec 15 04:19:27 PST 2010 [email protected]
* Tighten up what it means to be an "enumeration data constructor"
See Note [Enumeration types] in TyCon, and comments in Trac #4528
M ./compiler/iface/BuildTyCl.lhs -2 +6
M ./compiler/types/TyCon.lhs -1 +11
}}}
As a result you now get
{{{
T4528.hs:10:1:
Can't make a derived instance of `Enum (Foo a)':
`Foo' is not an enumeration type
(an enumeration consists of one or more nullary, non-GADT
constructors)
In the stand-alone deriving instance for `Enum (Foo a)'
}}}
A second patch fixes a bug in the byte code generator, whereby it didn't
know that an enumeration can (in GHC) have a phantom argument:
{{{
data T a = A | B | C
}}}
This crashes 7.0.1 when loaded into GHCi. Fixed by
{{{
Wed Dec 15 12:18:17 GMT 2010 [email protected]
* Allow enumerations to have phantom arguments.
The bytecode generator was being too eager.
Fixes Trac #4528, or rather, a near variant.
M ./compiler/ghci/ByteCodeGen.lhs -2 +2
}}}
Both have tests; both could be merged.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4528#comment:2>
GHC <http://www.haskell.org/ghc/>
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