[GHC] #8779: Exhaustiveness checks for pattern synonyms
GHC
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Wed Jun 8 09:08:58 UTC 2016
#8779: Exhaustiveness checks for pattern synonyms
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Reporter: nomeata | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler (Type | Version: 7.8.1
checker) | Keywords:
Resolution: | PatternSynonyms
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by simonpj):
What you say is attractive Reid, but consider a snoc-view of a list. We
might want to say that the two patterns `SnocNil` and `SnocCons` are
exhaustive, but the fact that they are really is something that needs
proof (`SnocCons` at least is defined via a view).
Moreover, if we match on `SnocCons` and miss out `SnocNil` we'd like to
report `SnocNil` as missing, rather than `[]`. And vice versa with
matching on `SnocNil` and omitting `SnocCons`.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8779#comment:32>
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