Hi Andrew,

I don't know whether it's intentional, but the patterns for "case line of" are not exaustive. Are you sure you do not expect anything else apart from a single "." or a line starting with '#'?

More below:

On Mon, May 5, 2008 at 1:45 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:
Neil Mitchell wrote:
hGetContents might be a different way to write a similar thing:

read_args h = do
    src <- hGetContents h
    let (has,rest) = span ("#" `isPrefixOf`) $ lines src
    return (map tail has)

Of course, depending on exactly the kind of IO control you need to do,
it may not work.
 
Please correct me if I am wrong; but the rest of the contents from the handle h will be unavailable after the evaluation of this function: it goes into a semi-closed state. (Correctly so: 'src' is supposed to have the entire contents obtained from h if needed.)

Another minor observation: if the partial pattern in the original code was intentional, then this is not exactly the same.

what about

read_args' :: [String] -> ([String],[String])
read_args' src = span ("#" `isPrefixOf`) $ lines src

and then using

s <- hGetContents
let (arg, rest) = read_args' $ lines s
...

So that you can get both the result and the remaining list of lines, in case you need them. Again, this does not exactly stop where there is a "." on a single line; it stops as soon as it gets a line without a '#'.

Abhay