4 ms·
Do you have any references for that? I looked through some Haskell documentation and didn't see anything warning about those functions being unsafe (although th
by camccann 17y ago
Do you have any references for that? I looked through some Haskell documentation and didn't see anything warning about those functions being unsafe (although there does seem to be an unsafeHGetContents in System.IO.Unsafe).
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.
- jfoutz 17y agoIt's just getContents (and brother hGetContents). 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.
- camccann 17y agoWell, I was confused because getContents seems to be of type "IO String": http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3AgetContents 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.
- shrughes 17y agoThe behavior of hGetContents is documented at http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#v%3AhGetContents http://www.haskell.org/ghc/docs/latest/html/libraries/base/S... . If you write do h <- openFile "foo.txt" ReadMode x <- hGetContents h putStr x you'll get different behavior than if you write do h <- openFile "foo.txt" ReadMode x <- hGetContents h hClose h putStr x In the first example, you'll print out the contents of the file. In the latter, you'll print out nothing.