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
  ...

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