Re: Proposal: add 'equating' function to Data.List

Put in a separate proposal for Data.List.uncons. It is a reasonable, self-contained function that encourages good style. The name has been commonly used and reinvented over and over and as a top level proposal we can have any bikeshedding discussion without derailing this one. I honestly thought it was already in there. -Edward

On Jul 18, 2014, at 5:19 PM, David Feuer wrote:

What I'd like for Data.List is

uncons :: [a] -> Maybe (a, [a]). uncons [] = Nothing uncons (a:as) = Just (a,as)

I believe Data.Text and maybe even Data.ByteString have similar functions. The main reason, I think:

The idiom

do x <- listToMaybe xss ... ... tail xss ...

is a bit ugly as the safety of tail xs depends implicitly on the fact that listToMaybe guards it, and because it treats the head and tail completely differently. Far prettier:

do (x,xs) <- uncons xss ...

_______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries