panic! initTc: unsolved constraints

New haskeller here, I was doing an exercise at http://exercism.io/exercises/haskell/rotational-cipher/readme and got the following error message from the compiler.

Compiling Main             ( RotationalCipher.hs, .stack-work/dist/x86_64-linux-tinfo6/Cabal-1.24.2.0/build/Main.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.2 for x86_64-unknown-linux):
	initTc: unsolved constraints
  WC {wc_insol =
        [W] find_a7hU :: t_a7hT[tau:1] (CHoleCan: find)
        [W] find_a7iF :: t_a7iE[tau:1] (CHoleCan: find)}

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

Progress: 16/17
--  While building custom Setup.hs for package rotational-cipher-1.1.0.1 using:
      /home/websterw/.stack/setup-exe-cache/x86_64-linux-tinfo6/Cabal-simple_mPHDZzAJ_1.24.2.0_ghc-8.0.2 --builddir=.stack-work/dist/x86_64-linux-tinfo6/Cabal-1.24.2.0 build lib:rotational-cipher test:test --ghc-options " -ddump-hi -ddump-to-file"
    Process exited with code: ExitFailure 1

I was using the normal project setup that exercism uses for this problem, with my code residing a file called RotationalCipher.hs. The contents of this file are as follows.

rotate :: Int -> String -> String
rotate n = map (rot n) 

rot :: Int -> Char -> Char
rot i c 
  | c `elem` ['a'..'z'] = let translate = zip (lowershift n) ['a'..'z'] in
      fst (find (\x -> snd x == c) translate)
  | c `elem` ['A'..'Z'] = let translate = zip (uppershift n) ['A'..'Z'] in
      fst (find (\x -> snd x == c) translate)
  | otherwise = c
  where lowershift n = take 26 $ drop n $ cycle ['a'..'z']
        uppershift n = take 26 $ drop n $ cycle ['A'..'Z']

The error occured when I ran stack test

I am using fedora linux as my operating system on x86_64

Trac metadata

Trac field	Value
Version	8.0.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture