"Committed_by_peb"

src/GF/Data/Utilities.hs

@@ -4,9 +4,9 @@
 -- Stability   : (stable)
 -- Portability : (portable)
 --
--- > CVS $Date: 2005/04/11 13:52:49 $ 
+-- > CVS $Date: 2005/05/09 09:28:44 $ 
 -- > CVS $Author: peb $
--- > CVS $Revision: 1.1 $
+-- > CVS $Revision: 1.2 $
 --
 -- Basic functions not in the standard libraries
 -----------------------------------------------------------------------------
@@ -14,6 +14,8 @@
 
 module GF.Data.Utilities where
 
+import Monad (liftM)
+
 -- * functions on lists
 
 sameLength :: [a] -> [a] -> Bool
@@ -21,6 +23,10 @@ sameLength [] [] = True
 sameLength (_:xs) (_:ys) = sameLength xs ys
 sameLength _ _ = False
 
+notLongerThan, longerThan :: Int -> [a] -> Bool
+notLongerThan n = null . snd . splitAt n
+longerThan    n = not . notLongerThan n
+
 lookupList :: Eq a => a -> [(a, b)] -> [b]
 lookupList a [] = []
 lookupList a (p:ps) | a == fst p = snd p : lookupList a ps
@@ -42,6 +48,18 @@ foldMerge merge zero = fm
 	  fm [a] = a
 	  fm abs = let (as, bs) = split abs in fm as `merge` fm bs
 
+select :: [a] -> [(a, [a])]
+select [] = []
+select (x:xs) = (x,xs) : [ (y,x:ys) | (y,ys) <- select xs ]
+
+updateNth :: (a -> a) -> Int -> [a] -> [a]
+updateNth update 0 (a : as) = update a : as
+updateNth update n (a : as) = a : updateNth update (n-1) as
+
+updateNthM :: Monad m => (a -> m a) -> Int -> [a] -> m [a]
+updateNthM update 0 (a : as) = liftM (:as) (update a)
+updateNthM update n (a : as) = liftM (a:)  (updateNthM update (n-1) as)
+
 -- * functions on pairs
 
 mapFst :: (a -> a') -> (a, b) -> (a', b)