[GHC] #10134: Pattern Matching Causes Infinite Type Error

[GHC]

#10134: Pattern Matching Causes Infinite Type Error
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        Reporter:  dongen            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.8.4
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by goldfire):

 This smells like a "Let should not be generalised" problem. dongen: Does
 enabling the `MonoLocalBinds` extension fix the problem? Conversely, in
 your one-module, no-dependencies version, does enabling `NoMonoLocalBinds`
 cause the problem to appear?

 The `TypeFamilies` extension implies `MonoLocalBinds`.

 My guess is that this is a case where using definitions whose types
 mention type families means that a `let` should not be generalised. And
 that will be hard to fix without enabling `MonoLocalBinds` by default.

 Interesting -- I'd love to see that minimal case!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10134#comment:13>
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