Curry: An Integrated Functional Logic Language

takeWhile _ [] = []
takeWhile p (x:xs) = if p x then x : takeWhile p xs else []
-- Return suffix without takeWhile prefix
dropWhile :: (a -> Bool) -> [a] -> [a]
dropWhile _ [] = []
dropWhile p (x:xs) = if p x then dropWhile p xs else x:xs
-- (span p xs) is equivalent to (takeWhile p xs, dropWhile p xs)
span :: (a -> Bool) -> [a] -> ([a],[a])
span _ [] = ([],[])
span p (x:xs)
| p x = let (ys,zs) = span p xs in (x:ys, zs)
| otherwise = ([],x:xs)
-- (break p xs) is equivalent to (takeWhile (not.p) xs, dropWhile (not.p) xs)
-- i.e., it breaks a list at the first occurrence of an element satisfying p
break :: (a -> Bool) -> [a] -> ([a],[a])
break p = span (not . p)
-- Break a string into list of lines where a line is terminated at a
-- newline character. The resulting lines do not contain newline characters.
lines :: String -> [String]
lines [] = []
lines (c:cs) = let (l,restcs) = splitline (c:cs) in l : lines restcs
where splitline [] = ([],[])
splitline (c:cs) = if c==’\n’
then ([],cs)
else let (ds,es) = splitline cs in (c:ds,es)
-- Concatenate a list of strings with terminating newlines
unlines :: [String] -> String
unlines ls = concatMap (++"\n") ls
-- Break a string into a list of words where the words are delimited by
-- white spaces.
words :: String -> [String]
words s = let s1 = dropWhile isSpace s
in if s1=="" then []
else let (w,s2) = break isSpace s1
in w : words s2
where
isSpace c = c == ’ ’ || c == ’\t’ || c == ’\n’ || c == ’\r’
-- Concatenate a list of strings with a blank between two strings.
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