Why is there no splitBy in the list module?
maeder at tzi.de
Thu Jul 13 08:51:37 EDT 2006
Donald Bruce Stewart schrieb:
> -- | The 'splitBy' function takes a predicate and splits the input
> -- list at each element which satisfies the predicate.
> splitBy :: (a -> Bool) -> [a] -> [[a]]
> splitBy p s =
> case s of
>  -> 
> _ -> let (l, r) = break p s in
> case r of
> _ : t@(_:_) -> l : splitBy p t
> _ -> [l]
> -- | The 'split' function splits the input list on each occurrence of
> -- the given element.
> split :: Eq a => a -> [a] -> [[a]]
> split c = splitBy (== c)
> prop_lines_split xs =
> lines xs == split '\n' xs
> prop_words_split xs =
> words xs == split ' ' xs
The last property is wrong. It must be:
words xs == filter (not . null) (split ' ' xs)
Another property of my suggested functions:
splitWords, splitLines, splitFields :: Eq a => a -> [a] -> [[a]]
id = concat . intersperse [c] . splitFields c -- :: [a] -> [a]
splitLines is equal to splitFields as long as there is no last seperator
(or terminator) element. splitWords can be easily derived from
splitLines or splitFields via "filter (not . null)".
splitFields c = splitLines c . (++ [c])
Which of the two versions splitFields or splitLines should get the
general name "split" is a matter of taste and of compatibility to the
currently incompatible Data.PackedString or (your) Data.ByteString.
If we cannot agree, I'ld suggest to keep (my) longer names, only.
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