{-# LANGUAGE Safe #-} {- arch-tag: List utilities main file Copyright (c) 2004-2011 John Goerzen <jgoerzen@complete.org> All rights reserved. For license and copyright information, see the file LICENSE -} {- | Module : Data.List.Utils Copyright : Copyright (C) 2004-2011 John Goerzen License : BSD3 Maintainer : John Goerzen <jgoerzen@complete.org> Stability : provisional Portability: portable This module provides various helpful utilities for dealing with lists. Written by John Goerzen, jgoerzen\@complete.org -} module Data.List.Utils(-- * Merging merge, mergeBy, -- * Tests startswith, endswith, contains, hasAny, -- * Association List Utilities {- | These functions are designed to augment the association list functions in "Data.List" and provide an interface similar to "Data.FiniteMap" or "Data.Map" for association lists. -} addToAL, delFromAL, flipAL, keysAL, valuesAL, hasKeyAL, -- ** Association List Conversions strFromAL, strToAL, -- * Conversions split, join, replace, genericJoin, takeWhileList, dropWhileList, spanList, breakList, -- ** Advanced Conversions WholeFunc(..), wholeMap, fixedWidth, -- * Fixed-Width and State Monad Utilities grab, -- * Miscellaneous countElem, elemRIndex, alwaysElemRIndex, seqList, subIndex, uniq -- -- * Sub-List Selection -- sub, ) where import Data.List(intersperse, concat, isPrefixOf, isSuffixOf, elemIndices, elemIndex, elemIndices, tails, find, findIndex, isInfixOf, nub) import Control.Monad.State(State, get, put) import Data.Maybe(isJust) {- | Merge two sorted lists into a single, sorted whole. Example: > merge [1,3,5] [1,2,4,6] -> [1,1,2,3,4,5,6] QuickCheck test property: prop_merge xs ys = merge (sort xs) (sort ys) == sort (xs ++ ys) where types = xs :: [Int] -} merge :: (Ord a) => [a] -> [a] -> [a] merge = mergeBy (compare) {- | Merge two sorted lists using into a single, sorted whole, allowing the programmer to specify the comparison function. QuickCheck test property: prop_mergeBy xs ys = mergeBy cmp (sortBy cmp xs) (sortBy cmp ys) == sortBy cmp (xs ++ ys) where types = xs :: [ (Int, Int) ] cmp (x1,_) (x2,_) = compare x1 x2 -} mergeBy :: (a -> a -> Ordering) -> [a] -> [a] -> [a] mergeBy cmp [] ys = ys mergeBy cmp xs [] = xs mergeBy cmp (allx@(x:xs)) (ally@(y:ys)) -- Ordering derives Eq, Ord, so the comparison below is valid. -- Explanation left as an exercise for the reader. -- Someone please put this code out of its misery. | (x `cmp` y) <= EQ = x : mergeBy cmp xs ally | otherwise = y : mergeBy cmp allx ys {- | Returns true if the given list starts with the specified elements; false otherwise. (This is an alias for "Data.List.isPrefixOf".) Example: > startswith "He" "Hello" -> True -} startswith :: Eq a => [a] -> [a] -> Bool startswith = isPrefixOf {- | Returns true if the given list ends with the specified elements; false otherwise. (This is an alias for "Data.List.isSuffixOf".) Example: > endswith "lo" "Hello" -> True -} endswith :: Eq a => [a] -> [a] -> Bool endswith = isSuffixOf {- | Returns true if the given list contains any of the elements in the search list. -} hasAny :: Eq a => [a] -- ^ List of elements to look for -> [a] -- ^ List to search -> Bool -- ^ Result hasAny [] _ = False -- An empty search list: always false hasAny _ [] = False -- An empty list to scan: always false hasAny search (x:xs) = if x `elem` search then True else hasAny search xs {- | Similar to Data.List.takeWhile, takes elements while the func is true. The function is given the remainder of the list to examine. -} takeWhileList :: ([a] -> Bool) -> [a] -> [a] takeWhileList _ [] = [] takeWhileList func list@(x:xs) = if func list then x : takeWhileList func xs else [] {- | Similar to Data.List.dropWhile, drops elements while the func is true. The function is given the remainder of the list to examine. -} dropWhileList :: ([a] -> Bool) -> [a] -> [a] dropWhileList _ [] = [] dropWhileList func list@(x:xs) = if func list then dropWhileList func xs else list {- | Similar to Data.List.span, but performs the test on the entire remaining list instead of just one element. @spanList p xs@ is the same as @(takeWhileList p xs, dropWhileList p xs)@ -} spanList :: ([a] -> Bool) -> [a] -> ([a], [a]) spanList _ [] = ([],[]) spanList func list@(x:xs) = if func list then (x:ys,zs) else ([],list) where (ys,zs) = spanList func xs {- | Similar to Data.List.break, but performs the test on the entire remaining list instead of just one element. -} breakList :: ([a] -> Bool) -> [a] -> ([a], [a]) breakList func = spanList (not . func) {- | Given a delimiter and a list (or string), split into components. Example: > split "," "foo,bar,,baz," -> ["foo", "bar", "", "baz", ""] > split "ba" ",foo,bar,,baz," -> [",foo,","r,,","z,"] -} split :: Eq a => [a] -> [a] -> [[a]] split _ [] = [] split delim str = let (firstline, remainder) = breakList (startswith delim) str in firstline : case remainder of [] -> [] x -> if x == delim then [] : [] else split delim (drop (length delim) x) {- | Given a list and a replacement list, replaces each occurance of the search list with the replacement list in the operation list. Example: >replace "," "." "127,0,0,1" -> "127.0.0.1" This could logically be thought of as: >replace old new l = join new . split old $ l -} replace :: Eq a => [a] -> [a] -> [a] -> [a] replace old new l = join new . split old $ l {- | Given a delimiter and a list of items (or strings), join the items by using the delimiter. Example: > join "|" ["foo", "bar", "baz"] -> "foo|bar|baz" -} join :: [a] -> [[a]] -> [a] join delim l = concat (intersperse delim l) {- | Like 'join', but works with a list of anything showable, converting it to a String. Examples: > genericJoin ", " [1, 2, 3, 4] -> "1, 2, 3, 4" > genericJoin "|" ["foo", "bar", "baz"] -> "\"foo\"|\"bar\"|\"baz\"" -} genericJoin :: Show a => String -> [a] -> String genericJoin delim l = join delim (map show l) {-# DEPRECATED contains "Use Data.List.isInfixOf, will be removed in MissingH 1.1.0" #-} {- | Returns true if the given parameter is a sublist of the given list; false otherwise. Example: > contains "Haskell" "I really like Haskell." -> True > contains "Haskell" "OCaml is great." -> False This function was submitted to GHC and was applied as 'Data.List.isInfixOf'. This function therefore is deprecated and will be removed in future versions. -} contains :: Eq a => [a] -> [a] -> Bool contains = isInfixOf -- above function submitted to GHC as Data.List.isInfixOf on 8/31/2006 {- | Adds the specified (key, value) pair to the given list, removing any existing pair with the same key already present. -} addToAL :: Eq key => [(key, elt)] -> key -> elt -> [(key, elt)] addToAL l key value = (key, value) : delFromAL l key {- | Removes all (key, value) pairs from the given list where the key matches the given one. -} delFromAL :: Eq key => [(key, a)] -> key -> [(key, a)] delFromAL l key = filter (\a -> (fst a) /= key) l {- | Returns the keys that comprise the (key, value) pairs of the given AL. Same as: >map fst -} keysAL :: [(key, a)] -> [key] keysAL = map fst {- | Returns the values the comprise the (key, value) pairs of the given AL. Same as: >map snd -} valuesAL :: [(a, value)] -> [value] valuesAL = map snd {- | Indicates whether or not the given key is in the AL. -} hasKeyAL :: Eq a => a -> [(a, b)] -> Bool hasKeyAL key list = elem key (keysAL list) {- | Flips an association list. Converts (key1, val), (key2, val) pairs to (val, [key1, key2]). -} flipAL :: (Eq key, Eq val) => [(key, val)] -> [(val, [key])] flipAL oldl = let worker :: (Eq key, Eq val) => [(key, val)] -> [(val, [key])] -> [(val, [key])] worker [] accum = accum worker ((k, v):xs) accum = case lookup v accum of Nothing -> worker xs ((v, [k]) : accum) Just y -> worker xs (addToAL accum v (k:y)) in worker oldl [] {- | Converts an association list to a string. The string will have one pair per line, with the key and value both represented as a Haskell string. This function is designed to work with [(String, String)] association lists, but may work with other types as well. -} strFromAL :: (Show a, Show b) => [(a, b)] -> String strFromAL inp = let worker (key, val) = show key ++ "," ++ show val in unlines . map worker $ inp {- | The inverse of 'strFromAL', this function reads a string and outputs the appropriate association list. Like 'strFromAL', this is designed to work with [(String, String)] association lists but may also work with other objects with simple representations. -} strToAL :: (Read a, Read b) => String -> [(a, b)] strToAL inp = let worker line = case reads line of [(key, remainder)] -> case remainder of ',':valstr -> (key, read valstr) _ -> error "Data.List.Utils.strToAL: Parse error on value" _ -> error "Data.List.Utils.strToAL: Parse error on key" in map worker (lines inp) {- FIXME TODO: sub -} {- | Returns a count of the number of times the given element occured in the given list. -} countElem :: Eq a => a -> [a] -> Int countElem i = length . filter (i==) {- | Returns the rightmost index of the given element in the given list. -} elemRIndex :: Eq a => a -> [a] -> Maybe Int elemRIndex item l = case reverse $ elemIndices item l of [] -> Nothing (x:_) -> Just x {- | Like elemRIndex, but returns -1 if there is nothing found. -} alwaysElemRIndex :: Eq a => a -> [a] -> Int alwaysElemRIndex item list = case elemRIndex item list of Nothing -> -1 Just x -> x {- | Forces the evaluation of the entire list. -} seqList :: [a] -> [a] seqList [] = [] seqList list@(x:xs) = seq (seqList xs) list -------------------------------------------------- -- Advanced Conversions -------------------------------------------------- {- | The type used for functions for 'wholeMap'. See 'wholeMap' for details. -} newtype WholeFunc a b = WholeFunc ([a] -> (WholeFunc a b, [a], [b])) {- | This is an enhanced version of the concatMap or map functions in Data.List. Unlike those functions, this one: * Can consume a varying number of elements from the input list during each iteration * Can arbitrarily decide when to stop processing data * Can return a varying number of elements to insert into the output list * Can actually switch processing functions mid-stream * Is not even restricted to processing the input list intact The function used by wholeMap, of type 'WholeFunc', is repeatedly called with the input list. The function returns three things: the function to call for the next iteration (if any), what remains of the input list, and the list of output elements generated during this iteration. The return value of 'wholeMap' is the concatenation of the output element lists from all iterations. Processing stops when the remaining input list is empty. An example of a 'WholeFunc' is 'fixedWidth'. -} wholeMap :: WholeFunc a b -> [a] -> [b] wholeMap _ [] = [] -- Empty input, empty output. wholeMap (WholeFunc func) inplist = let (nextfunc, nextlist, output) = func inplist in output ++ wholeMap nextfunc nextlist {- | A parser designed to process fixed-width input fields. Use it with 'wholeMap'. The Int list passed to this function is the list of the field widths desired from the input. The result is a list of those widths, if possible. If any of the input remains after processing this list, it is added on as the final element in the result list. If the input is less than the sum of the requested widths, then the result list will be short the appropriate number of elements, and its final element may be shorter than requested. Examples: >wholeMap (fixedWidth [1, 2, 3]) "1234567890" > --> ["1","23","456","7890"] >wholeMap (fixedWidth (repeat 2)) "123456789" > --> ["12","34","56","78","9"] >wholeMap (fixedWidth []) "123456789" > --> ["123456789"] >wholeMap (fixedWidth [5, 3, 6, 1]) "Hello, This is a test." > --> ["Hello",", T","his is"," ","a test."] -} fixedWidth :: [Int] -> WholeFunc a [a] fixedWidth len = WholeFunc (fixedWidthFunc len) where -- Empty input: Empty output, stop fixedWidthFunc _ [] = ((fixedWidth []), [], []) -- Empty length: Stop here. fixedWidthFunc [] x = ((fixedWidth []), [], [x]) -- Stuff to process: Do it. fixedWidthFunc (len:lenxs) input = (fixedWidth lenxs, next, [this]) where (this, next) = splitAt len input {- | Helps you pick out fixed-width components from a list. Example: >conv :: String -> (String,String) >conv = runState $ > do f3 <- grab 3 > n2 <- grab 2 > return $ f3 ++ "," ++ n2 > >main = print $ conv "TestIng" Prints: >("Tes,tI","ng") -} grab :: Int -> State [a] [a] grab count = do g <- get (x, g') <- return $ splitAt count g put g' return x {- | Similar to Data.List.elemIndex. Instead of looking for one element in a list, this function looks for the first occurance of a sublist in the list, and returns the index of the first element of that occurance. If there is no such list, returns Nothing. If the list to look for is the empty list, will return Just 0 regardless of the content of the list to search. Examples: >subIndex "foo" "asdfoobar" -> Just 3 >subIndex "foo" [] -> Nothing >subIndex "" [] -> Just 0 >subIndex "" "asdf" -> Just 0 >subIndex "test" "asdftestbartest" -> Just 4 >subIndex [(1::Int), 2] [0, 5, 3, 2, 1, 2, 4] -> Just 4 -} subIndex :: Eq a => [a] -> [a] -> Maybe Int subIndex substr str = findIndex (isPrefixOf substr) (tails str) {- | Given a list, returns a new list with all duplicate elements removed. For example: >uniq "Mississippi" -> "Misp" You should not rely on this function necessarily preserving order, though the current implementation happens to. This function is not compatible with infinite lists. This is presently an alias for Data.List.nub -} uniq :: Eq a => [a] -> [a] uniq = nub ----- same as --uniq (x:xs) = x : [y | y <- uniq xs, y /= x]