{-# OPTIONS -fno-implicit-prelude #-} ----------------------------------------------------------------------------- -- | -- Module : Data.List -- Copyright : (c) The University of Glasgow 2001 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : provisional -- Portability : portable -- -- Operations on lists. -- -----------------------------------------------------------------------------moduleData.List( -- * Basic functions (++) -- :: [a] -> [a] -> [a] ,head-- :: [a] -> a ,last-- :: [a] -> a ,tail-- :: [a] -> [a] ,init-- :: [a] -> [a] ,null-- :: [a] -> Bool ,length-- :: [a] -> Int -- * List transformations ,map-- :: (a -> b) -> [a] -> [b] ,reverse-- :: [a] -> [a] ,intersperse-- :: a -> [a] -> [a] ,intercalate,transpose-- :: [[a]] -> [[a]] -- * Reducing lists (folds) ,foldl-- :: (a -> b -> a) -> a -> [b] -> a ,foldl'-- :: (a -> b -> a) -> a -> [b] -> a ,foldl1-- :: (a -> a -> a) -> [a] -> a ,foldr-- :: (a -> b -> b) -> b -> [a] -> b ,foldr1-- :: (a -> a -> a) -> [a] -> a -- ** Special folds ,concat-- :: [[a]] -> [a] ,concatMap-- :: (a -> [b]) -> [a] -> [b] ,and-- :: [Bool] -> Bool ,or-- :: [Bool] -> Bool ,any-- :: (a -> Bool) -> [a] -> Bool ,all-- :: (a -> Bool) -> [a] -> Bool ,sum-- :: (Num a) => [a] -> a ,product-- :: (Num a) => [a] -> a ,maximum-- :: (Ord a) => [a] -> a ,minimum-- :: (Ord a) => [a] -> a -- * Building lists -- ** Scans ,scanl-- :: (a -> b -> a) -> a -> [b] -> [a] ,scanl1-- :: (a -> a -> a) -> [a] -> [a] ,scanr-- :: (a -> b -> b) -> b -> [a] -> [b] ,scanr1-- :: (a -> a -> a) -> [a] -> [a] -- ** Accumulating maps ,mapAccumL-- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c]) ,mapAccumR-- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c]) -- ** Infinite lists ,iterate-- :: (a -> a) -> a -> [a] ,repeat-- :: a -> [a] ,replicate-- :: Int -> a -> [a] ,cycle-- :: [a] -> [a] -- ** Unfolding ,unfoldr-- :: (b -> Maybe (a, b)) -> b -> [a] -- * Sublists -- ** Extracting sublists ,take-- :: Int -> [a] -> [a] ,drop-- :: Int -> [a] -> [a] ,splitAt-- :: Int -> [a] -> ([a], [a]) ,takeWhile-- :: (a -> Bool) -> [a] -> [a] ,dropWhile-- :: (a -> Bool) -> [a] -> [a] ,span-- :: (a -> Bool) -> [a] -> ([a], [a]) ,break-- :: (a -> Bool) -> [a] -> ([a], [a]) ,group-- :: Eq a => [a] -> [[a]] ,inits-- :: [a] -> [[a]] ,tails-- :: [a] -> [[a]] -- ** Predicates ,isPrefixOf-- :: (Eq a) => [a] -> [a] -> Bool ,isSuffixOf-- :: (Eq a) => [a] -> [a] -> Bool ,isInfixOf-- :: (Eq a) => [a] -> [a] -> Bool -- * Searching lists -- ** Searching by equality ,elem-- :: a -> [a] -> Bool ,notElem-- :: a -> [a] -> Bool ,lookup-- :: (Eq a) => a -> [(a,b)] -> Maybe b -- ** Searching with a predicate ,find-- :: (a -> Bool) -> [a] -> Maybe a ,filter-- :: (a -> Bool) -> [a] -> [a] ,partition-- :: (a -> Bool) -> [a] -> ([a], [a]) -- * Indexing lists -- | These functions treat a list @xs@ as a indexed collection, -- with indices ranging from 0 to @'length' xs - 1@. , (!!) -- :: [a] -> Int -> a ,elemIndex-- :: (Eq a) => a -> [a] -> Maybe Int ,elemIndices-- :: (Eq a) => a -> [a] -> [Int] ,findIndex-- :: (a -> Bool) -> [a] -> Maybe Int ,findIndices-- :: (a -> Bool) -> [a] -> [Int] -- * Zipping and unzipping lists ,zip-- :: [a] -> [b] -> [(a,b)] ,zip3,zip4,zip5,zip6,zip7,zipWith-- :: (a -> b -> c) -> [a] -> [b] -> [c] ,zipWith3,zipWith4,zipWith5,zipWith6,zipWith7,unzip-- :: [(a,b)] -> ([a],[b]) ,unzip3,unzip4,unzip5,unzip6,unzip7-- * Special lists -- ** Functions on strings ,lines-- :: String -> [String] ,words-- :: String -> [String] ,unlines-- :: [String] -> String ,unwords-- :: [String] -> String -- ** \"Set\" operations ,nub-- :: (Eq a) => [a] -> [a] ,delete-- :: (Eq a) => a -> [a] -> [a] , (\\) -- :: (Eq a) => [a] -> [a] -> [a] ,union-- :: (Eq a) => [a] -> [a] -> [a] ,intersect-- :: (Eq a) => [a] -> [a] -> [a] -- ** Ordered lists ,sort-- :: (Ord a) => [a] -> [a] ,insert-- :: (Ord a) => a -> [a] -> [a] -- * Generalized functions -- ** The \"@By@\" operations -- | By convention, overloaded functions have a non-overloaded -- counterpart whose name is suffixed with \`@By@\'. -- *** User-supplied equality (replacing an @Eq@ context) -- | The predicate is assumed to define an equivalence. ,nubBy-- :: (a -> a -> Bool) -> [a] -> [a] ,deleteBy-- :: (a -> a -> Bool) -> a -> [a] -> [a] ,deleteFirstsBy-- :: (a -> a -> Bool) -> [a] -> [a] -> [a] ,unionBy-- :: (a -> a -> Bool) -> [a] -> [a] -> [a] ,intersectBy-- :: (a -> a -> Bool) -> [a] -> [a] -> [a] ,groupBy-- :: (a -> a -> Bool) -> [a] -> [[a]] -- *** User-supplied comparison (replacing an @Ord@ context) -- | The function is assumed to define a total ordering. ,sortBy-- :: (a -> a -> Ordering) -> [a] -> [a] ,insertBy-- :: (a -> a -> Ordering) -> a -> [a] -> [a] ,maximumBy-- :: (a -> a -> Ordering) -> [a] -> a ,minimumBy-- :: (a -> a -> Ordering) -> [a] -> a -- ** The \"@generic@\" operations -- | The prefix \`@generic@\' indicates an overloaded function that -- is a generalized version of a "Prelude" function. ,genericLength-- :: (Integral a) => [b] -> a ,genericTake-- :: (Integral a) => a -> [b] -> [b] ,genericDrop-- :: (Integral a) => a -> [b] -> [b] ,genericSplitAt-- :: (Integral a) => a -> [b] -> ([b], [b]) ,genericIndex-- :: (Integral a) => [b] -> a -> b ,genericReplicate-- :: (Integral a) => a -> b -> [b] ,stripPrefix)whereimportData.MaybeimportData.Char (isSpace)infix5\\-- newer versions of cpp don't like lines ending with a backslash -- ----------------------------------------------------------------------------- -- List functions -- | The 'elemIndex' function returns the index of the first element -- in the given list which is equal (by '==') to the query element, -- or 'Nothing' if there is no such element.elemIndex::Eqa=>a->[a]->MaybeIntelemIndexx=findIndex(x==) -- | The 'elemIndices' function extends 'elemIndex', by returning the -- indices of all elements equal to the query element, in ascending order.elemIndices::Eqa=>a->[a]->[Int]elemIndicesx=findIndices(x==) -- | The 'find' function takes a predicate and a list and returns the -- first element in the list matching the predicate, or 'Nothing' if -- there is no such element.find::(a->Bool)->[a]->Maybeafindp=listToMaybe.filterp-- | The 'findIndex' function takes a predicate and a list and returns -- the index of the first element in the list satisfying the predicate, -- or 'Nothing' if there is no such element.findIndex::(a->Bool)->[a]->MaybeIntfindIndexp=listToMaybe.findIndicesp-- | The 'findIndices' function extends 'findIndex', by returning the -- indices of all elements satisfying the predicate, in ascending order.findIndices::(a->Bool)->[a]->[Int]findIndicespxs=[i|(x,i)<-zipxs[0..],px] -- | The 'isPrefixOf' function takes two lists and returns 'True' -- iff the first list is a prefix of the second.isPrefixOf::(Eqa)=>[a]->[a]->BoolisPrefixOf[]_=TrueisPrefixOf_[]=FalseisPrefixOf(x:xs) (y:ys)=x==y&&isPrefixOfxsys-- | The 'isSuffixOf' function takes two lists and returns 'True' -- iff the first list is a suffix of the second. -- Both lists must be finite.isSuffixOf::(Eqa)=>[a]->[a]->BoolisSuffixOfxy=reversex`isPrefixOf`reverseyisInfixOf::(Eqa)=>[a]->[a]->BoolisInfixOfxy=undefinedstripPrefix::Eqa=>[a]->[a]->Maybe[a]stripPrefix=undefined-- | The 'nub' function removes duplicate elements from a list. -- In particular, it keeps only the first occurrence of each element. -- (The name 'nub' means \`essence\'.) -- It is a special case of 'nubBy', which allows the programmer to supply -- their own equality test.nub::(Eqa)=>[a]->[a] -- stolen from HBCnubl=nub'l[] -- 'wherenub'[]_=[] -- 'nub'(x:xs)ls-- '|x`elem`ls=nub'xsls-- '|otherwise=x:nub'xs(x:ls) -- ' -- | The 'nubBy' function behaves just like 'nub', except it uses a -- user-supplied equality predicate instead of the overloaded '==' -- function.nubBy::(a->a->Bool)->[a]->[a]nubByeql=nubBy'l[]wherenubBy'[]_=[]nubBy'(y:ys)xs|elem_byeqyxs=nubBy'ysxs|otherwise=y:nubBy'ys(y:xs) -- Not exported: -- Note that we keep the call to `eq` with arguments in the -- same order as in the reference implementation -- 'xs' is the list of things we've seen so far, -- 'y' is the potential new elementelem_by::(a->a->Bool)->a->[a]->Boolelem_by__[]=Falseelem_byeqy(x:xs)=x`eq`y||elem_byeqyxs-- | 'delete' @x@ removes the first occurrence of @x@ from its list argument. -- For example, -- -- > delete 'a' "banana" == "bnana" -- -- It is a special case of 'deleteBy', which allows the programmer to -- supply their own equality test.delete::(Eqa)=>a->[a]->[a]delete=deleteBy(==) -- | The 'deleteBy' function behaves like 'delete', but takes a -- user-supplied equality predicate.deleteBy::(a->a->Bool)->a->[a]->[a]deleteBy__[]=[]deleteByeqx(y:ys)=ifx`eq`ythenyselsey:deleteByeqxys-- | The '\\' function is list difference ((non-associative). -- In the result of @xs@ '\\' @ys@, the first occurrence of each element of -- @ys@ in turn (if any) has been removed from @xs@. Thus -- -- > (xs ++ ys) \\ xs == ys. -- -- It is a special case of 'deleteFirstsBy', which allows the programmer -- to supply their own equality test. (\\)::(Eqa)=>[a]->[a]->[a] (\\)=foldl(flipdelete) -- | The 'union' function returns the list union of the two lists. -- For example, -- -- > "dog" `union` "cow" == "dogcw" -- -- Duplicates, and elements of the first list, are removed from the -- the second list, but if the first list contains duplicates, so will -- the result. -- It is a special case of 'unionBy', which allows the programmer to supply -- their own equality test.union::(Eqa)=>[a]->[a]->[a]union=unionBy(==) -- | The 'unionBy' function is the non-overloaded version of 'union'.unionBy::(a->a->Bool)->[a]->[a]->[a]unionByeqxsys=xs++foldl(flip(deleteByeq)) (nubByeqys)xs-- | The 'intersect' function takes the list intersection of two lists. -- For example, -- -- > [1,2,3,4] `intersect` [2,4,6,8] == [2,4] -- -- If the first list contains duplicates, so will the result. -- It is a special case of 'intersectBy', which allows the programmer to -- supply their own equality test.intersect::(Eqa)=>[a]->[a]->[a]intersect=intersectBy(==) -- | The 'intersectBy' function is the non-overloaded version of 'intersect'.intersectBy::(a->a->Bool)->[a]->[a]->[a]intersectByeqxsys=[x|x<-xs,any(eqx)ys] -- | The 'intersperse' function takes an element and a list and -- \`intersperses\' that element between the elements of the list. -- For example, -- -- > intersperse ',' "abcde" == "a,b,c,d,e"intersperse::a->[a]->[a]intersperse_[]=[]intersperse_[x]=[x]interspersesep(x:xs)=x:sep:interspersesepxsintercalate::[a]->[[a]]->[a]intercalatexsxss=concat(interspersexsxss) -- | The 'transpose' function transposes the rows and columns of its argument. -- For example, -- -- > transpose [[1,2,3],[4,5,6]] == [[1,4],[2,5],[3,6]]transpose::[[a]]->[[a]]transpose[]=[]transpose([]:xss)=transposexsstranspose((x:xs):xss)=(x:[h|(h:t)<-xss]):transpose(xs:[t|(h:t)<-xss]) -- | The 'partition' function takes a predicate a list and returns -- the pair of lists of elements which do and do not satisfy the -- predicate, respectively; i.e., -- -- > partition p xs == (filter p xs, filter (not . p) xs)partition::(a->Bool)->[a]->([a],[a]) {-# INLINE partition #-}partitionpxs=foldr(selectp) ([],[])xsselectpx(ts,fs)|px=(x:ts,fs)|otherwise=(ts,x:fs) -- | The 'mapAccumL' function behaves like a combination of 'map' and -- 'foldl'; it applies a function to each element of a list, passing -- an accumulating parameter from left to right, and returning a final -- value of this accumulator together with the new list.mapAccumL::(acc->x->(acc,y)) -- Function of elt of input list -- and accumulator, returning new -- accumulator and elt of result list->acc-- Initial accumulator->[x] -- Input list->(acc, [y]) -- Final accumulator and result listmapAccumL_s[]=(s, [])mapAccumLfs(x:xs)=(s'',y:ys)where(s',y)=fsx(s'',ys)=mapAccumLfs'xs-- | The 'mapAccumR' function behaves like a combination of 'map' and -- 'foldr'; it applies a function to each element of a list, passing -- an accumulating parameter from right to left, and returning a final -- value of this accumulator together with the new list.mapAccumR::(acc->x->(acc,y)) -- Function of elt of input list -- and accumulator, returning new -- accumulator and elt of result list->acc-- Initial accumulator->[x] -- Input list->(acc, [y]) -- Final accumulator and result listmapAccumR_s[]=(s, [])mapAccumRfs(x:xs)=(s'',y:ys)where(s'',y)=fs'x(s',ys)=mapAccumRfsxs-- | The 'insert' function takes an element and a list and inserts the -- element into the list at the last position where it is still less -- than or equal to the next element. In particular, if the list -- is sorted before the call, the result will also be sorted. -- It is a special case of 'insertBy', which allows the programmer to -- supply their own comparison function.insert::Orda=>a->[a]->[a]insertels=insertBy(compare)els-- | The non-overloaded version of 'insert'.insertBy::(a->a->Ordering)->a->[a]->[a]insertBy_x[]=[x]insertBycmpxys@(y:ys')=casecmpxyofGT->y:insertBycmpxys'_->x:ys-- | The 'maximumBy' function takes a comparison function and a list -- and returns the greatest element of the list by the comparison function. -- The list must be finite and non-empty.maximumBy::(a->a->Ordering)->[a]->amaximumBy_[]=error"List.maximumBy: empty list"maximumBycmpxs=foldl1maxxswheremaxxy=casecmpxyofGT->x_->y-- | The 'minimumBy' function takes a comparison function and a list -- and returns the least element of the list by the comparison function. -- The list must be finite and non-empty.minimumBy::(a->a->Ordering)->[a]->aminimumBy_[]=error"List.minimumBy: empty list"minimumBycmpxs=foldl1minxswhereminxy=casecmpxyofGT->y_->x-- | The 'genericLength' function is an overloaded version of 'length'. In -- particular, instead of returning an 'Int', it returns any type which is -- an instance of 'Num'. It is, however, less efficient than 'length'.genericLength::(Numi)=>[b]->igenericLength[]=0genericLength(_:l)=1+genericLengthl-- | The 'genericTake' function is an overloaded version of 'take', which -- accepts any 'Integral' value as the number of elements to take.genericTake::(Integrali)=>i->[a]->[a]genericTake0_=[]genericTake_[]=[]genericTaken(x:xs)|n>0=x:genericTake(n-1)xsgenericTake__=error"List.genericTake: negative argument" -- | The 'genericDrop' function is an overloaded version of 'drop', which -- accepts any 'Integral' value as the number of elements to drop.genericDrop::(Integrali)=>i->[a]->[a]genericDrop0xs=xsgenericDrop_[]=[]genericDropn(_:xs)|n>0=genericDrop(n-1)xsgenericDrop__=error"List.genericDrop: negative argument" -- | The 'genericSplitAt' function is an overloaded version of 'splitAt', which -- accepts any 'Integral' value as the position at which to split.genericSplitAt::(Integrali)=>i->[b]->([b],[b])genericSplitAt0xs=([],xs)genericSplitAt_[]=([],[])genericSplitAtn(x:xs)|n>0=(x:xs',xs'')where(xs',xs'')=genericSplitAt(n-1)xsgenericSplitAt__=error"List.genericSplitAt: negative argument" -- | The 'genericIndex' function is an overloaded version of '!!', which -- accepts any 'Integral' value as the index.genericIndex::(Integrala)=>[b]->a->bgenericIndex(x:_) 0=xgenericIndex(_:xs)n|n>0=genericIndexxs(n-1)|otherwise=error"List.genericIndex: negative argument."genericIndex__=error"List.genericIndex: index too large." -- | The 'genericReplicate' function is an overloaded version of 'replicate', -- which accepts any 'Integral' value as the number of repetitions to make.genericReplicate::(Integrali)=>i->a->[a]genericReplicatenx=genericTaken(repeatx) -- | The 'zip4' function takes four lists and returns a list of -- quadruples, analogous to 'zip'.zip4::[a]->[b]->[c]->[d]->[(a,b,c,d)]zip4=zipWith4(,,,) -- | The 'zip5' function takes five lists and returns a list of -- five-tuples, analogous to 'zip'.zip5::[a]->[b]->[c]->[d]->[e]->[(a,b,c,d,e)]zip5=zipWith5(,,,,) -- | The 'zip6' function takes six lists and returns a list of six-tuples, -- analogous to 'zip'.zip6::[a]->[b]->[c]->[d]->[e]->[f]->[(a,b,c,d,e,f)]zip6=zipWith6(,,,,,) -- | The 'zip7' function takes seven lists and returns a list of -- seven-tuples, analogous to 'zip'.zip7::[a]->[b]->[c]->[d]->[e]->[f]->[g]->[(a,b,c,d,e,f,g)]zip7=zipWith7(,,,,,,) -- | The 'zipWith4' function takes a function which combines four -- elements, as well as four lists and returns a list of their point-wise -- combination, analogous to 'zipWith'.zipWith4::(a->b->c->d->e)->[a]->[b]->[c]->[d]->[e]zipWith4z(a:as) (b:bs) (c:cs) (d:ds)=zabcd:zipWith4zasbscsdszipWith4_____=[] -- | The 'zipWith5' function takes a function which combines five -- elements, as well as five lists and returns a list of their point-wise -- combination, analogous to 'zipWith'.zipWith5::(a->b->c->d->e->f)->[a]->[b]->[c]->[d]->[e]->[f]zipWith5z(a:as) (b:bs) (c:cs) (d:ds) (e:es)=zabcde:zipWith5zasbscsdseszipWith5______=[] -- | The 'zipWith6' function takes a function which combines six -- elements, as well as six lists and returns a list of their point-wise -- combination, analogous to 'zipWith'.zipWith6::(a->b->c->d->e->f->g)->[a]->[b]->[c]->[d]->[e]->[f]->[g]zipWith6z(a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs)=zabcdef:zipWith6zasbscsdsesfszipWith6_______=[] -- | The 'zipWith7' function takes a function which combines seven -- elements, as well as seven lists and returns a list of their point-wise -- combination, analogous to 'zipWith'.zipWith7::(a->b->c->d->e->f->g->h)->[a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]zipWith7z(a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs) (g:gs)=zabcdefg:zipWith7zasbscsdsesfsgszipWith7________=[] -- | The 'unzip4' function takes a list of quadruples and returns four -- lists, analogous to 'unzip'.unzip4::[(a,b,c,d)]->([a],[b],[c],[d])unzip4=foldr(\(a,b,c,d)~(as,bs,cs,ds)->(a:as,b:bs,c:cs,d:ds)) ([],[],[],[]) -- | The 'unzip5' function takes a list of five-tuples and returns five -- lists, analogous to 'unzip'.unzip5::[(a,b,c,d,e)]->([a],[b],[c],[d],[e])unzip5=foldr(\(a,b,c,d,e)~(as,bs,cs,ds,es)->(a:as,b:bs,c:cs,d:ds,e:es)) ([],[],[],[],[]) -- | The 'unzip6' function takes a list of six-tuples and returns six -- lists, analogous to 'unzip'.unzip6::[(a,b,c,d,e,f)]->([a],[b],[c],[d],[e],[f])unzip6=foldr(\(a,b,c,d,e,f)~(as,bs,cs,ds,es,fs)->(a:as,b:bs,c:cs,d:ds,e:es,f:fs)) ([],[],[],[],[],[]) -- | The 'unzip7' function takes a list of seven-tuples and returns -- seven lists, analogous to 'unzip'.unzip7::[(a,b,c,d,e,f,g)]->([a],[b],[c],[d],[e],[f],[g])unzip7=foldr(\(a,b,c,d,e,f,g)~(as,bs,cs,ds,es,fs,gs)->(a:as,b:bs,c:cs,d:ds,e:es,f:fs,g:gs)) ([],[],[],[],[],[],[]) -- | The 'deleteFirstsBy' function takes a predicate and two lists and -- returns the first list with the first occurrence of each element of -- the second list removed.deleteFirstsBy::(a->a->Bool)->[a]->[a]->[a]deleteFirstsByeq=foldl(flip(deleteByeq)) -- | The 'group' function takes a list and returns a list of lists such -- that the concatenation of the result is equal to the argument. Moreover, -- each sublist in the result contains only equal elements. For example, -- -- > group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"] -- -- It is a special case of 'groupBy', which allows the programmer to supply -- their own equality test.group::Eqa=>[a]->[[a]]group=groupBy(==) -- | The 'groupBy' function is the non-overloaded version of 'group'.groupBy::(a->a->Bool)->[a]->[[a]]groupBy_[]=[]groupByeq(x:xs)=(x:ys):groupByeqzswhere(ys,zs)=span(eqx)xs-- | The 'inits' function returns all initial segments of the argument, -- shortest first. For example, -- -- > inits "abc" == ["","a","ab","abc"] --inits::[a]->[[a]]inits[]=[[]]inits(x:xs)=[[]]++map(x:) (initsxs) -- | The 'tails' function returns all final segments of the argument, -- longest first. For example, -- -- > tails "abc" == ["abc", "bc", "c",""] --tails::[a]->[[a]]tails[]=[[]]tailsxxs@(_:xs)=xxs:tailsxs------------------------------------------------------------------------------ -- Quick Sort algorithm taken from HBC's QSort library. -- | The 'sort' function implements a stable sorting algorithm. -- It is a special case of 'sortBy', which allows the programmer to supply -- their own comparison function.sort::(Orda)=>[a]->[a] -- | The 'sortBy' function is the non-overloaded version of 'sort'.sortBy::(a->a->Ordering)->[a]->[a]sortBycmpl=mergesortcmplsortl=mergesortcomparel{- Quicksort replaced by mergesort, 14/5/2002. From: Ian LynaghI am curious as to why the List.sort implementation in GHC is a quicksort algorithm rather than an algorithm that guarantees n log n time in the worst case? I have attached a mergesort implementation along with a few scripts to time it's performance, the results of which are shown below (* means it didn't finish successfully - in all cases this was due to a stack overflow). If I heap profile the random_list case with only 10000 then I see random_list peaks at using about 2.5M of memory, whereas in the same program using List.sort it uses only 100k. Input style Input length Sort data Sort alg User time stdin 10000 random_list sort 2.82 stdin 10000 random_list mergesort 2.96 stdin 10000 sorted sort 31.37 stdin 10000 sorted mergesort 1.90 stdin 10000 revsorted sort 31.21 stdin 10000 revsorted mergesort 1.88 stdin 100000 random_list sort * stdin 100000 random_list mergesort * stdin 100000 sorted sort * stdin 100000 sorted mergesort * stdin 100000 revsorted sort * stdin 100000 revsorted mergesort * func 10000 random_list sort 0.31 func 10000 random_list mergesort 0.91 func 10000 sorted sort 19.09 func 10000 sorted mergesort 0.15 func 10000 revsorted sort 19.17 func 10000 revsorted mergesort 0.16 func 100000 random_list sort 3.85 func 100000 random_list mergesort * func 100000 sorted sort 5831.47 func 100000 sorted mergesort 2.23 func 100000 revsorted sort 5872.34 func 100000 revsorted mergesort 2.24 -} mergesort::(a->a->Ordering)->[a]->[a]mergesortcmp=mergesort'cmp.mapwrapmergesort'::(a->a->Ordering)->[[a]]->[a]mergesort'cmp[]=[]mergesort'cmp[xs]=xsmergesort'cmpxss=mergesort'cmp(merge_pairscmpxss)merge_pairs::(a->a->Ordering)->[[a]]->[[a]]merge_pairscmp[]=[]merge_pairscmp[xs]=[xs]merge_pairscmp(xs:ys:xss)=mergecmpxsys:merge_pairscmpxssmerge::(a->a->Ordering)->[a]->[a]->[a]mergecmpxs[]=xsmergecmp[]ys=ysmergecmp(x:xs) (y:ys)=casex`cmp`yofGT->y:mergecmp(x:xs)ys_->x:mergecmpxs(y:ys)wrap::a->[a]wrapx=[x] {- OLD: qsort version -- qsort is stable and does not concatenate. qsort :: (a -> a -> Ordering) -> [a] -> [a] -> [a] qsort _ [] r = r qsort _ [x] r = x:r qsort cmp (x:xs) r = qpart cmp x xs [] [] r -- qpart partitions and sorts the sublists qpart :: (a -> a -> Ordering) -> a -> [a] -> [a] -> [a] -> [a] -> [a] qpart cmp x [] rlt rge r = -- rlt and rge are in reverse order and must be sorted with an -- anti-stable sorting rqsort cmp rlt (x:rqsort cmp rge r) qpart cmp x (y:ys) rlt rge r = case cmp x y of GT -> qpart cmp x ys (y:rlt) rge r _ -> qpart cmp x ys rlt (y:rge) r -- rqsort is as qsort but anti-stable, i.e. reverses equal elements rqsort :: (a -> a -> Ordering) -> [a] -> [a] -> [a] rqsort _ [] r = r rqsort _ [x] r = x:r rqsort cmp (x:xs) r = rqpart cmp x xs [] [] r rqpart :: (a -> a -> Ordering) -> a -> [a] -> [a] -> [a] -> [a] -> [a] rqpart cmp x [] rle rgt r = qsort cmp rle (x:qsort cmp rgt r) rqpart cmp x (y:ys) rle rgt r = case cmp y x of GT -> rqpart cmp x ys rle (y:rgt) r _ -> rqpart cmp x ys (y:rle) rgt r -} -- | The 'unfoldr' function is a \`dual\' to 'foldr': while 'foldr' -- reduces a list to a summary value, 'unfoldr' builds a list from -- a seed value. The function takes the element and returns 'Nothing' -- if it is done producing the list or returns 'Just' @(a,b)@, in which -- case, @a@ is a prepended to the list and @b@ is used as the next -- element in a recursive call. For example, -- -- > iterate f == unfoldr (\x -> Just (x, f x)) -- -- In some cases, 'unfoldr' can undo a 'foldr' operation: -- -- > unfoldr f' (foldr f z xs) == xs -- -- if the following holds: -- -- > f' (f x y) = Just (x,y) -- > f' z = Nothingunfoldr::(b->Maybe(a,b))->b->[a]unfoldrfb=casefbofJust(a,new_b)->a:unfoldrfnew_bNothing->[] -- ----------------------------------------------------------------------------- -- | A strict version of 'foldl'.foldl'::(a->b->a)->a->[b]->afoldl'fa[]=afoldl'fa(x:xs)=leta'=faxina'`seq`foldl'fa'xs

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(HTML for this module was generated on 2013-11-05. About the conversion tool.)