[Haskell-cafe] wordsBy in the base libraries?
ndmitchell at gmail.com
Mon Oct 22 05:50:44 EDT 2007
We certainly need a function to split a list into sections. Whether it
be wordsBy, or something like linesBy, or some new split variant.
> > > wordsBy :: (a -> Bool) -> [a] -> [[a]]
> > > wordsBy p s = case dropWhile p s of
> > >  -> 
> > > s':rest -> (s':w) : wordsBy p s''
> > > where (w, s'') = break p rest
You are still over by one test. Try instead:
wordsBy :: (a -> Bool) -> [a] -> [[a]]
wordsBy p s = case dropWhile p s of
 -> 
s':rest -> (s':w) : wordsBy p (drop 1 s'')
where (w, s'') = break p rest
The supero paper (http://www-users.cs.york.ac.uk/~ndm/supero/) has a
very short explanation of this.
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