#3927: Incomplete/overlapped pattern warnings + GADTs = inadequate
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Reporter: simonpj | Owner: simonpj
Type: bug | Status: new
Priority: high | Milestone: 7.0.1
Component: Compiler | Version: 6.12.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by simonpj):
Ok so you are saying that GHC is giving correct messages, but you'd like
to see the warning become an error.
I don't think we'll do this:
* Technically dead GADT case alternatives are not ill-typed. (Just look
at any GADT paper.)
* More pragmatically, GHC can spot ''some'' dead code, but not ''all''
dead code. Eg
{{{
f x y | x > y = ...
| x <= y = ....
| otherwise = ...dead code...
}}}
Even thinking only of type equalities, the solver cannot guarantee to
find all unsatisfiable contexts. So it'd be tricky to pin down exactly
which programs were errors (and hence would not even compile) and which
were only warnings (and hence would run).
All in all, I think it's best as it is. That said, the original bug
report of this ticket still stands.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3927#comment:8>
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