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)
Yes, that would be the sensible name. However, I don't think it deserves to be in the standard libraries :-) If anyone feels it should be, that sounds like it should be a separate proposal from nubOrd.
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? :-)
Yes, that does seem like the correct name for it. Again, I don't think it's a massively useful function - the Accum functions just aren't as useful anymore now Monads are better understood. Thanks Neil ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================