Well, I was confused because getContents seems to be of type "IO String": http://www.haskell.org/ghc/docs/latest/html/libraries/base/P...
I can see why a lazy input stream could make things opaque even in a completely type-safe program, though.
Using getContents is fine for a quick way to slurp in a file, but it's like doing a read without checking for -1. Since haskell is lazy, figuring out why an underlying read failed can be fairly confusing.
If you think your program is doing IO and there's no IO type getting in the way, unsafePerformIO is lurking in the darkness.