[GHC] #10356: Couldn't match type ‘a’ with ‘Int’ / ‘a’ is untouchable / inside the constraints ()

[GHC]

#10356: Couldn't match type ‘a’ with ‘Int’ / ‘a’ is untouchable / inside the
constraints ()
-------------------------------------+-------------------------------------
              Reporter:  radix       |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  normal      |         Milestone:
             Component:  Compiler    |           Version:  7.10.1
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:  x86_64      |   Type of failure:  Compile-time
  (amd64)                            |  crash
             Test Case:              |        Blocked By:
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 Sadly I'm a Haskell newbie, so this won't be a very good bug report, but I
 am working on a codebase and I triggered a GHC bug (at least according to
 GHC itself).

 {{{
 Building json-log-viewer-0.0.1...
 Preprocessing executable 'json-log-viewer' for json-log-viewer-0.0.1...
 [3 of 3] Compiling Main             ( src/Main.hs, dist/build/json-log-
 viewer/json-log-viewer-tmp/Main.o )

 src/Main.hs:316:41:
     Couldn't match type ‘a’ with ‘Int’
       ‘a’ is untouchable
         inside the constraints ()
         bound by the inferred type of refreshMessages :: IO ()
         at src/Main.hs:(300,7)-(324,48)ghc: panic! (the 'impossible'
 happened)
   (GHC version 7.10.1 for x86_64-apple-darwin):
         No skolem info: a_al2w[sk]

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 I saved the state of the code in a git branch and put it here:
 https://github.com/radix/json-log-viewer/tree/ghc-bug

 I'll also attach my list of cabal dependencies installed. The only tricky
 one is that I'm working off of an unreleased version of `vty-ui`, at this
 revision: https://github.com/jtdaugherty/vty-
 ui/commit/c3a0c4b660119a4d5862a6f549a98739a3fc5fa7


 I also don't know if the program is "valid" -- I'm in the middle of a
 refactor, and it's a big cluttered program that I know is very poorly
 written. Sorry about that. I would not usually report a bug in such a
 situation but the compiler implored me to, so I am.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10356>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler