[Haskell-beginners] Picking apart getLine
anguscomber at gmail.com
Tue Jan 7 16:54:15 UTC 2014
Before looking at getLine, I can understand this:
getnumber :: IO Int
getnumber = do x <- getChar
if isDigit x then
return (ord x - ord '0')
OK, it is not a very useful function but at least I understand it. return
is required so that the function returns an IO Int.
But I don't understand this:
getLine' :: IO String
getLine' = do x <- getChar
if x == '\n' then
xs <- getLine'
I can understand what will happen if a user enters a newline (only).
return  brings the empty list into the monadic world.
But what is happening if x is not a newline?
xs <- getLine' will recursively call getChar and retrieve another character
from the input stream. But it will do this BEFORE the return (x:xs) - so
what is happening to all the head elements in the list - the x element?
It is difficult to picture in my mind how this is working. I understand
recursion but this looks tricky.
Can someone help me work this out?
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Beginners