
Mitchell, Neil wrote:
Hi
Were we to keep it, do you have a better naming suggestion?
[Warning: untested code]
filterAccum :: (acc -> x -> (acc,Bool)) -> acc -> [x] -> (acc, [x]) filterAccum f a [] = (a, []) filterAccum f a (x:xs) = (an, [x|b]++rest) where (a2,b) = f a x (an,rest) = filterAccum f a2 xs
This follows the type of mapAccumL, and is more general than your function.
can we call it filterAccumL then? It took me a while to figure out from the code whether it was truly an "L" or "R" version, and in principle there could be filterAccumR (although I don't know why we'd want it)
You could change the utility function to be (acc -> x -> (acc,Maybe y)) to get a variant that is more general than both mapAccum and filterAccum.
in which case the result type would be (acc, [y]), and it would have a similar type and semantics to Data.Maybe.mapMaybe :: (a -> Maybe b) -> [a] -> [b] .. maybeAccumL? :-) -Isaac