2011/4/19 Daniel Schüssler
Hello,
for reference, said instance is:
instance Monad m => Monad (Iteratee a m) where return x = yield x (Chunks [])
m0 >>= f = ($ m0) $ fix $ \bind m -> Iteratee $ runIteratee m >>= \r1 -> case r1 of Continue k -> return (Continue (bind . k)) Error err -> return (Error err) Yield x (Chunks []) -> runIteratee (f x) Yield x extra -> runIteratee (f x) >>= \r2 -> case r2 of Continue k -> runIteratee (k extra) Error err -> return (Error err) Yield x' _ -> return (Yield x' extra)
The thing I don't understand yet is the last line: Why is it OK to discard the leftover input from the (f x) Iteratee and yield just the leftover input from the first one (m0)?
On that stage no input was given to (f x), we just runned it without anything and it already yielded something. So whatever it yielded must be without leftovers. Now, that's what I get from reading the code. I don't remember if it is explicitly allowed or forbidden for an iteratee to generate leftovers out of nowhere. My guess is that it doesn't make much sense to allow it. Cheers, -- Felipe.