[GHC] #11066: Inacessible branch should be warning - otherwise breaks type soundness?
GHC
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Tue Nov 7 17:17:32 UTC 2017
#11066: Inacessible branch should be warning - otherwise breaks type soundness?
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Reporter: rrnewton | Owner: (none)
Type: bug | Status: new
Priority: high | Milestone: 8.4.1
Component: Compiler | Version: 7.10.2
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Incorrect | Unknown/Multiple
warning at compile-time | Test Case:
Blocked By: | Blocking:
Related Tickets: #8128, #8740 | Differential Rev(s): Phab:D1454
Wiki Page: |
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Comment (by simonpj):
> If what you're saying is that the fact that its type family Gcd :: Nat
-> Nat -> Nat, rather than that other form, that is causing the problem
Precisely. If `Gcd` is nullary, then `Gcd a b` can never be equal to `1`.
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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11066#comment:32>
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