[GHC] #10876: stack overflow regression

13 Sep 2015

      #10876: stack overflow regression
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              Reporter:  dmwit       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.2
  (Type checker)                     |
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
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 I would like to teach GHC that `<=` is transitive. I tried a module that
 looks like this:

 {{{#!hs
 {-# LANGUAGE GADTs, Rank2Types, TypeOperators #-}
 import GHC.TypeLits
 trans :: (a <= b, b <= c) => ((a <= c) => d) -> d
 trans = undefined
 }}}

 In 7.8, this is a type error; in 7.10 the compiler thinks a long time
 before emitting a stack overflow exception.

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10876
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