#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 Saizan):
Replying to [comment:6 simonpj]:
> Pumpkin, GHC is quite correct in its warnings about your code. If you
put in the "error" lines in your code above, then GHC correctly warns
that those branches are inaccessible:
> {{{
> T3927b.hs:26:11:
> Inaccessible code in
> a pattern with constructor `Fz', in an equation for `index'
> Couldn't match type `Nz' with `Ns n'
> In the pattern: Fz
> In an equation for `index':
> index Nil Fz
> = error
> "GHC shouldn't even let me write this combination of ..."
> }}}
but with the latest GHC HEAD that's an error not just a warning (ghci
refuses to load the module, at least), so it actually implements what
pumpkin is advocating in comment #7
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3927#comment:10>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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