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As an exercise from RWH, I needed to write a function that splits a list every time the predicate is false (words == splitWith (== ' ') for strings):

splitWith :: (a -> Bool) -> [a] -> [[a]]
splitWith _ [] = []
splitWith p xs
    | null pre = splitWith p post'
    | otherwise = pre : splitWith p post'
    where
        (pre, post) = break p xs
        post' = if null post then [] else tail post

My concern is the if..then..else chain; it seems "forced". I have to make sure that post isn't null, or it will crash on the call to tail.

Is there a better way to write this?

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You can gin up a safe version of tail lickety-split by using drop 1.

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  • \$\begingroup\$ Seriously -_-. I've actually used that before. Thank you; that solves it nicely. \$\endgroup\$ – Carcigenicate Sep 7 '14 at 2:34

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