Could you elaborate, please? Or point me to a discussion of the issues with said functions? Thanks!
More practically, `getContent` is evil because it locks the file it is reading for an unbounded amount of time: as long as it's content (the giant string representing the file), isn't either out of scope (and eventually garbage collected) or fully evaluated.
That can be a problem if you intent to open loads of files (you could hit the OS limit) or if you want to modify the file after reading part of it.
Lazy IO is therefore quite embarrassing. Several people are working at hopefully safer alternatives right now.
Is there's something I'm missing that says "hey, this function uses unsafePerformIO behind the scenes" or whatnot? Being not very experienced with Haskell I'm a little worried about library functions being unsafe without me realizing it.
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.
I can see why a lazy input stream could make things opaque even in a completely type-safe program, though.
If you write
do h <- openFile "foo.txt" ReadMode
x <- hGetContents h
putStr x
do h <- openFile "foo.txt" ReadMode
x <- hGetContents h
hClose h
putStr x