Simplifier ticks exhausted: a 10-line case

I was trying to define a function that could take itself as an argument.

newtype MobiusFn a = MobiusFn {
    func :: MobiusFn a -> a
}

spin :: MobiusFn a -> a
spin mf = func mf mf

Use it to find suffixes of a String

suffixes :: String -> [String]
suffixes = spin $ MobiusFn suffixesMF
    where suffixesMF _ [] = []
          suffixesMF mf s@(_:xs) = s : spin mf xs

Add main and compile

main = readLn >>= (print . suffixes)

The compiler panicked with

[1 of 1] Compiling Main             ( test.hs, test.o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for i386-unknown-linux):
        Simplifier ticks exhausted
  When trying UnfoldingDone mf_s1UD

But if we ignore the empty string case, it works well with non-empty strings.

suffixes :: String -> [String]
suffixes = spin $ MobiusFn suffixesMF
    where suffixesMF _ s@[_] = [s]
          suffixesMF mf s@(_:xs) = s : spin mf xs

Two versions tested.

GHC version 8.0.1 for i386-unknown-linux
GHC version 7.10.3 for i386-unknown-linux

Thank you for reading.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler
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