[Haskell-cafe] Unfoldr love
jgbailey at gmail.com
Thu Oct 25 18:52:47 EDT 2007
In my best Homer Simposon voice - "unfoldr - is there anything it can't do?"
I have strange unfoldr love right now. I'm probably too impressed by
this function, but it takes a string and splits it into a list of
words, while keeping "quoted" phrases together:
phrasesAndWords :: String -> [String]
let startsWith w c = [c] `isPrefixOf` w
endsWith w c = [c] `isSuffixOf` w
buildPhrases  = Nothing
| w `startsWith` '"' = -- A word starts with a '"', now
look for ending '"'
let (p, rest) = break (`endsWith` '"') (w:ws)
case () of
() | null p -> Just ((init . tail) w, ws) --
single word in quotes
| null rest -> Just ((tail . unwords) p, rest)
-- No ending quote
-- Some amount of words in the phrase and some not
| otherwise -> Just ((init . tail) (unwords (p
++ [head rest])), tail rest)
| otherwise = Just (w, ws)
-- Use of words makes sure any valid quotes appear at beginning or
-- end of a word.
unfoldr buildPhrases . words
Of course it's not a full parser (no nested quotes or escaping) but
who would think unfoldr could do that?
p.s. Style comments, improvements welcome.
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