[GHC] #15692: GHC panic from pattern synonyms + deferred type errors
GHC
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Thu Oct 4 15:03:40 UTC 2018
#15692: GHC panic from pattern synonyms + deferred type errors
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Reporter: Iceland_jack | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.6.1
Resolution: | Keywords:
| PatternSynonyms
Operating System: Unknown/Multiple | Architecture:
Type of failure: Compile-time | Unknown/Multiple
crash or panic | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
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Comment (by Simon Peyton Jones <simonpj@…>):
In [changeset:"9ebfa03d9e9cbf79f698b5d4bd39e799e4e9a02c/ghc" 9ebfa03/ghc]:
{{{
#!CommitTicketReference repository="ghc"
revision="9ebfa03d9e9cbf79f698b5d4bd39e799e4e9a02c"
Fail fast on pattern synonyms
We were recovering too eagerly from errors in pattern-synonym
type inference, leading to a cascade of confusing follow up errors
(Trac #15685, #15692).
The underlying issue is that a pattern synonym should have a closed,
fixed type, with no unification variables in it. But it wasn't!
Fixing this made me change the interface to simplifyInfer slightly.
Instead of /emitting/ a residual implication constraint, it
now /returns/ it, so that the caller can decide what to do.
}}}
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15692#comment:3>
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