Hi, This is a pretty simple problem to fix. (>>=) has type IO a -> (a -> IO b) -> IO b. 'readFile my_file' has type IO String, so this means whatever comes on the RHS of >>= should have type (String -> IO b). In your case, it doesn't. It has type String -> [something], but the [something] isn't an IO type. Hint: you need to put a call to 'return' in there. - Hal On Mon, 2003-09-15 at 06:55, Frederic BELLOC wrote:
HI, I have a recurrent probleme with function readFile and Monad : it is that i try to get a line, transform it and stock it in a list and what i want is that function return me the list. But hugs say me that in
readFile my_file >>= \s -> map cons_line (lines s) readFile is a IO String type but is used here as [[Char]] type... and i don't know what to do...
Ghc say me that is the lambda abstraction that fails with "map cons_line (lines s)" , he couldn't match IO against [] !
Help me please, i understand well (i hope) how Monad work but here i don't see a solution.
Sorry for my poor english but i'm already a student.
Thanks for all. -- -- Hal Daume III | hdaume@isi.edu "Arrest this man, he talks in maths." | www.isi.edu/~hdaume