[Haskell-cafe] A common pattern

Andrew Coppin andrewcoppin at btinternet.com
Mon May 5 06:29:04 EDT 2008

Abhay Parvate wrote:
> 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 '#'?

It's reading a wire protocol, so if you hit anything else there's been a 
protocol error. Arguably I should probably catch this case and report it 
gracefully. But really, there isn't much you could usefully do in this 


> 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.)

Quite so. If I was going with this approach, I'd have to call 
hGetContents and then parse the entire stream and act on it.

For my current application, which is basically a server that receives 
requests and then replies to them, I *think* you could possibly do that. 
If, however, there were to be some command that said "hey, disregard 
everything I just said, and switch to this new parsing mode..." then I'd 
have a problem implementing that this way.

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