[GHC] #13787: The compiler told me to report this. I have no idea what happened

[GHC]

#13787: The compiler told me to report this. I have no idea what happened
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        Reporter:  gleb_dianov       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.2
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Description changed by gleb_dianov:

@@ -37,0 +37,4 @@
+
+ UPD.
+ I updated to lts-8.16. Then I commented out the function and compiled the
+ project and when I uncommented it the compiler didn't crash

New description:

 Hi,
 Here is the error:

 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-unknown-linux):
         initTc: unsolved constraints
   WC {wc_insol = [W] err_aaeS :: t_aaeR[tau:1] (CHoleCan: err)}


 {{{#!hs
 teach :: l ~ S l' => ErrorFunction m -> ErrorFunction o -> LearningRate ->
 Vector (Example i o) m -> Network i l o -> Either StopCriteria (Either
 Error Iterations) -> NetowrkArgs i l o -> NetworkArgs i l o
 teach totalErr errF learnRate examples stopCriteria network args =
 teachNetwork network 0
     where teachNetwork :: Network i l o -> Iterations -> Network i l o
           teachNetwork net i
             | not $ shouldStop stopCriteria (networkError net) i =
 teachNetwork (foldl updateNetworkHelper net examples) (i + 1)
             | otherwise = net

           networkError :: Network i l o -> Error
           networkError = undefined

           updateNetworkHelper :: Network i l o -> Example i o -> Network i
 l o
           updateNetworkHelper net@(layer :~~ netTail) example = if example
 ^. output == runNetwork net (examples ^. input) then net else snd $
 updateNetwork layer netTail errF (example ^. inputs) (example ^. outputs)
 }}}

 This function broke the compiler. Here is a link to the git repo with this
 code (module Network) https://gitlab.com/gleb_dianov/neural-haskell

 With this project I wanted to show how cool Haskell is, but now I can only
 show how GHC crashes :(

 UPD.
 I updated to lts-8.16. Then I commented out the function and compiled the
 project and when I uncommented it the compiler didn't crash

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13787#comment:2>
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