I was fighting with Haskell last weekend. At first, I couldn't install some missing libraries with Cabal, and then, when trying to find out what's wrong, I ended up removing the whole Haskell installation — only to find out I could no longer install neither the Haskell Platform nor even just Cabal Install! The warnings I would see were more or less about the use of the single quote in source code:
Preprocessing library text-0.11.2.3...
Data/Text.hs:6:52:
warning: missing terminating ' character [-Winvalid-pp-token]
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