[GHC] #11652: Cyclical dependencies aren't reported in pure functions

[GHC]

#11652: Cyclical dependencies aren't reported in pure functions
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        Reporter:  keynan            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ezyang):

 Solving this problem in general would amount to solving the halting
 problem but I would definitely like to see some heuristics to give
 warnings in cases like this.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11652#comment:1>
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