In my case leftover is not important. But in common case... Just an idea...
What if we provide iterWhile :: Iteratee a m () -> Iteratee a m b -> Iteratee a m b The first Iteratee only control when the result should be yeilded and feed an input to second Iteratee. Then we can change manyToOne to manyToOne' :: Iteratee a m () -> [Iteratee a m b] -> Iteratee a m [b] manyToOne' iw = iterWhile iw . manyToOne 2011/4/29 Felipe Almeida Lessa <felipe.le...@gmail.com> > On Fri, Apr 29, 2011 at 6:32 AM, John Lato <jwl...@gmail.com> wrote: > > If you do this, the user needs to take care to order the iteratees so > that > > the last iteratee has small leftovers. Consider: > > > > manyToOne [consumeALot, return ()] > > > > In this case, the entire stream consumed by the first iteratee will need > to > > be retained and passed on by manyToOne. In many cases, the user may not > > know how much each iteratee will consume, which can make these semantics > > problematic. > > > > Iteratee has 'enumPair', (renamed 'zip' in HEAD) which returns the > leftovers > > from whichever iteratee consumes more. This avoids the problem of > retaining > > extra data, and seems simpler to reason about. Although if you really > need > > to consume a predictable amount of data, the safest is probably to run > the > > whole thing in a 'take'. > > My motivation is: in general it is difficult (impossible?) to choose > the iteratee that consumed more data because you don't know what the > data is. For example, if you give 'Chunks [a,b]' to two iteratees and > one of them returns 'Chunks [c]' and the other one returns 'Chunks > [d]', which one consumed more data? The answer is that it depends on > the types. If they are Ints, both consumed the same, if they are > ByteStrings, you would need to check if one is prefix of the other. > What if one returns 'Chunks [c]' and the other one returns 'Chunks > [d,e]'? If they are ByteStrings, should we compare 'c' against 'd ++ > e'? > > So I thought it would be easier to program with an API that is > predictable and immune to changes in block sizes. If you don't want > leftovers, just use 'manyToOne [..., dropWhile (const True)]', which > guarantees that you won't leak. > > Cheers, > > -- > Felipe. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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