-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/
-- | Combinator library for splitting lists.
--
-- A collection of various methods for splitting lists into parts, akin
-- to the "split" function found in several mainstream languages. Here is
-- its tale:
--
-- Once upon a time the standard Data.List module held no function
-- for splitting a list into parts according to a delimiter. Many a brave
-- lambda-knight strove to add such a function, but their striving was in
-- vain, for Lo, the Supreme Council fell to bickering amongst themselves
-- what was to be the essential nature of the One True Function which
-- could cleave a list in twain (or thrain, or any required number of
-- parts).
--
-- And thus came to pass the split package, comprising divers functions
-- for splitting a list asunder, each according to its nature. And the
-- Supreme Council had no longer any grounds for argument, for the
-- favored method of each was contained therein.
--
-- To get started, see the Data.List.Split module.
@package split
@version 0.2.3.5
-- | Implementation module for Data.List.Split, a combinator library
-- for splitting lists. See the Data.List.Split documentation for
-- more description and examples.
module Data.List.Split.Internals
-- | A splitting strategy.
data Splitter a
Splitter :: Delimiter a -> DelimPolicy -> CondensePolicy -> EndPolicy -> EndPolicy -> Splitter a
-- | What delimiter to split on
[delimiter] :: Splitter a -> Delimiter a
-- | What to do with delimiters (drop from output, keep as separate
-- elements in output, or merge with previous or following chunks)
[delimPolicy] :: Splitter a -> DelimPolicy
-- | What to do with multiple consecutive delimiters
[condensePolicy] :: Splitter a -> CondensePolicy
-- | Drop an initial blank?
[initBlankPolicy] :: Splitter a -> EndPolicy
-- | Drop a final blank?
[finalBlankPolicy] :: Splitter a -> EndPolicy
-- | The default splitting strategy: keep delimiters in the output as
-- separate chunks, don't condense multiple consecutive delimiters into
-- one, keep initial and final blank chunks. Default delimiter is the
-- constantly false predicate.
--
-- Note that defaultSplitter should normally not be used; use
-- oneOf, onSublist, or whenElt instead, which are
-- the same as the defaultSplitter with just the delimiter
-- overridden.
--
-- The defaultSplitter strategy with any delimiter gives a
-- maximally information-preserving splitting strategy, in the sense that
-- (a) taking the concat of the output yields the original list,
-- and (b) given only the output list, we can reconstruct a
-- Splitter which would produce the same output list again given
-- the original input list. This default strategy can be overridden to
-- allow discarding various sorts of information.
defaultSplitter :: Splitter a
-- | A delimiter is a list of predicates on elements, matched by some
-- contiguous subsequence of a list.
newtype Delimiter a
Delimiter :: [a -> Bool] -> Delimiter a
-- | Try to match a delimiter at the start of a list, either failing or
-- decomposing the list into the portion which matched the delimiter and
-- the remainder.
matchDelim :: Delimiter a -> [a] -> Maybe ([a], [a])
-- | What to do with delimiters?
data DelimPolicy
-- | Drop delimiters from the output.
Drop :: DelimPolicy
-- | Keep delimiters as separate chunks of the output.
Keep :: DelimPolicy
-- | Keep delimiters in the output, prepending them to the following chunk.
KeepLeft :: DelimPolicy
-- | Keep delimiters in the output, appending them to the previous chunk.
KeepRight :: DelimPolicy
-- | What to do with multiple consecutive delimiters?
data CondensePolicy
-- | Condense into a single delimiter.
Condense :: CondensePolicy
-- | Keep consecutive delimiters separate, but don't insert blank chunks in
-- between them.
DropBlankFields :: CondensePolicy
-- | Insert blank chunks between consecutive delimiters.
KeepBlankFields :: CondensePolicy
-- | What to do with a blank chunk at either end of the list (i.e.
-- when the list begins or ends with a delimiter).
data EndPolicy
DropBlank :: EndPolicy
KeepBlank :: EndPolicy
-- | Tag chunks as delimiters or text.
data Chunk a
Delim :: [a] -> Chunk a
Text :: [a] -> Chunk a
-- | Internal representation of a split list that tracks which pieces are
-- delimiters and which aren't.
type SplitList a = [Chunk a]
-- | Untag a Chunk.
fromElem :: Chunk a -> [a]
-- | Test whether a Chunk is a delimiter.
isDelim :: Chunk a -> Bool
-- | Test whether a Chunk is text.
isText :: Chunk a -> Bool
-- | Given a delimiter to use, split a list into an internal representation
-- with chunks tagged as delimiters or text. This transformation is
-- lossless; in particular,
--
--
-- concatMap fromElem (splitInternal d l) == l.
--
splitInternal :: Delimiter a -> [a] -> SplitList a
-- | Given a split list in the internal tagged representation, produce a
-- new internal tagged representation corresponding to the final output,
-- according to the strategy defined by the given Splitter.
postProcess :: Splitter a -> SplitList a -> SplitList a
-- | Drop delimiters if the DelimPolicy is Drop.
doDrop :: DelimPolicy -> SplitList a -> SplitList a
-- | Condense multiple consecutive delimiters into one if the
-- CondensePolicy is Condense.
doCondense :: CondensePolicy -> SplitList a -> SplitList a
-- | Insert blank chunks between any remaining consecutive delimiters
-- (unless the condense policy is DropBlankFields), and at the
-- beginning or end if the first or last element is a delimiter.
insertBlanks :: CondensePolicy -> SplitList a -> SplitList a
-- | Insert blank chunks between consecutive delimiters.
insertBlanks' :: CondensePolicy -> SplitList a -> SplitList a
-- | Merge delimiters into adjacent chunks according to the
-- DelimPolicy.
doMerge :: DelimPolicy -> SplitList a -> SplitList a
-- | Merge delimiters with adjacent chunks to the right (yes, that's not a
-- typo: the delimiters should end up on the left of the chunks, so they
-- are merged with chunks to their right).
mergeLeft :: SplitList a -> SplitList a
-- | Merge delimiters with adjacent chunks to the left.
mergeRight :: SplitList a -> SplitList a
-- | Drop an initial blank chunk according to the given EndPolicy.
dropInitial :: EndPolicy -> SplitList a -> SplitList a
-- | Drop a final blank chunk according to the given EndPolicy.
dropFinal :: EndPolicy -> SplitList a -> SplitList a
-- | Split a list according to the given splitting strategy. This is how to
-- "run" a Splitter that has been built using the other
-- combinators.
split :: Splitter a -> [a] -> [[a]]
-- | A splitting strategy that splits on any one of the given elements. For
-- example:
--
--
-- split (oneOf "xyz") "aazbxyzcxd" == ["aa","z","b","x","","y","","z","c","x","d"]
--
oneOf :: Eq a => [a] -> Splitter a
-- | A splitting strategy that splits on the given list, when it is
-- encountered as an exact subsequence. For example:
--
--
-- split (onSublist "xyz") "aazbxyzcxd" == ["aazb","xyz","cxd"]
--
--
-- Note that splitting on the empty list is a special case, which splits
-- just before every element of the list being split. For example:
--
--
-- split (onSublist "") "abc" == ["","","a","","b","","c"]
-- split (dropDelims . dropBlanks $ onSublist "") "abc" == ["a","b","c"]
--
--
-- However, if you want to break a list into singleton elements like
-- this, you are better off using chunksOf 1, or better
-- yet, map (:[]).
onSublist :: Eq a => [a] -> Splitter a
-- | A splitting strategy that splits on any elements that satisfy the
-- given predicate. For example:
--
--
-- split (whenElt (<0)) [2,4,-3,6,-9,1] == [[2,4],[-3],[6],[-9],[1]]
--
whenElt :: (a -> Bool) -> Splitter a
-- | Drop delimiters from the output (the default is to keep them). For
-- example,
--
--
-- split (oneOf ":") "a:b:c" == ["a", ":", "b", ":", "c"]
-- split (dropDelims $ oneOf ":") "a:b:c" == ["a", "b", "c"]
--
dropDelims :: Splitter a -> Splitter a
-- | Keep delimiters in the output by prepending them to adjacent chunks.
-- For example:
--
--
-- split (keepDelimsL $ oneOf "xyz") "aazbxyzcxd" == ["aa","zb","x","y","zc","xd"]
--
keepDelimsL :: Splitter a -> Splitter a
-- | Keep delimiters in the output by appending them to adjacent chunks.
-- For example:
--
--
-- split (keepDelimsR $ oneOf "xyz") "aazbxyzcxd" == ["aaz","bx","y","z","cx","d"]
--
keepDelimsR :: Splitter a -> Splitter a
-- | Condense multiple consecutive delimiters into one. For example:
--
--
-- split (condense $ oneOf "xyz") "aazbxyzcxd" == ["aa","z","b","xyz","c","x","d"]
-- split (dropDelims $ oneOf "xyz") "aazbxyzcxd" == ["aa","b","","","c","d"]
-- split (condense . dropDelims $ oneOf "xyz") "aazbxyzcxd" == ["aa","b","c","d"]
--
condense :: Splitter a -> Splitter a
-- | Don't generate a blank chunk if there is a delimiter at the beginning.
-- For example:
--
--
-- split (oneOf ":") ":a:b" == ["",":","a",":","b"]
-- split (dropInitBlank $ oneOf ":") ":a:b" == [":","a",":","b"]
--
dropInitBlank :: Splitter a -> Splitter a
-- | Don't generate a blank chunk if there is a delimiter at the end. For
-- example:
--
--
-- split (oneOf ":") "a:b:" == ["a",":","b",":",""]
-- split (dropFinalBlank $ oneOf ":") "a:b:" == ["a",":","b",":"]
--
dropFinalBlank :: Splitter a -> Splitter a
-- | Don't generate blank chunks between consecutive delimiters. For
-- example:
--
--
-- split (oneOf ":") "::b:::a" == ["",":","",":","b",":","",":","",":","a"]
-- split (dropInnerBlanks $ oneOf ":") "::b:::a" == ["", ":",":","b",":",":",":","a"]
--
dropInnerBlanks :: Splitter a -> Splitter a
-- | Drop all blank chunks from the output, and condense consecutive
-- delimiters into one. Equivalent to dropInitBlank .
-- dropFinalBlank . condense. For example:
--
--
-- split (oneOf ":") "::b:::a" == ["",":","",":","b",":","",":","",":","a"]
-- split (dropBlanks $ oneOf ":") "::b:::a" == ["::","b",":::","a"]
--
dropBlanks :: Splitter a -> Splitter a
-- | Make a strategy that splits a list into chunks that all start with the
-- given subsequence (except possibly the first). Equivalent to
-- dropInitBlank . keepDelimsL . onSublist.
-- For example:
--
--
-- split (startsWith "app") "applyapplicativeapplaudapproachapple" == ["apply","applicative","applaud","approach","apple"]
--
startsWith :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all start with one
-- of the given elements (except possibly the first). Equivalent to
-- dropInitBlank . keepDelimsL . oneOf. For
-- example:
--
--
-- split (startsWithOneOf ['A'..'Z']) "ACamelCaseIdentifier" == ["A","Camel","Case","Identifier"]
--
startsWithOneOf :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all end with the
-- given subsequence, except possibly the last. Equivalent to
-- dropFinalBlank . keepDelimsR .
-- onSublist. For example:
--
--
-- split (endsWith "ly") "happilyslowlygnarlylily" == ["happily","slowly","gnarly","lily"]
--
endsWith :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all end with one
-- of the given elements, except possibly the last. Equivalent to
-- dropFinalBlank . keepDelimsR . oneOf.
-- For example:
--
--
-- split (condense $ endsWithOneOf ".,?! ") "Hi, there! How are you?" == ["Hi, ","there! ","How ","are ","you?"]
--
endsWithOneOf :: Eq a => [a] -> Splitter a
-- | Split on any of the given elements. Equivalent to split .
-- dropDelims . oneOf. For example:
--
--
-- splitOneOf ";.," "foo,bar;baz.glurk" == ["foo","bar","baz","glurk"]
--
splitOneOf :: Eq a => [a] -> [a] -> [[a]]
-- | Split on the given sublist. Equivalent to split .
-- dropDelims . onSublist. For example:
--
--
-- splitOn ".." "a..b...c....d.." == ["a","b",".c","","d",""]
--
--
-- In some parsing combinator frameworks this is also known as
-- sepBy.
--
-- Note that this is the right inverse of the intercalate function
-- from Data.List, that is,
--
--
-- intercalate x . splitOn x === id
--
--
-- splitOn x . intercalate x is the identity on
-- certain lists, but it is tricky to state the precise conditions under
-- which this holds. (For example, it is not enough to say that
-- x does not occur in any elements of the input list. Working
-- out why is left as an exercise for the reader.)
splitOn :: Eq a => [a] -> [a] -> [[a]]
-- | Split on elements satisfying the given predicate. Equivalent to
-- split . dropDelims . whenElt. For
-- example:
--
--
-- splitWhen (<0) [1,3,-4,5,7,-9,0,2] == [[1,3],[5,7],[0,2]]
--
splitWhen :: (a -> Bool) -> [a] -> [[a]]
-- | Split into chunks terminated by the given subsequence. Equivalent to
-- split . dropFinalBlank . dropDelims .
-- onSublist. For example:
--
--
-- endBy ";" "foo;bar;baz;" == ["foo","bar","baz"]
--
--
-- Note also that the lines function from Data.List is
-- equivalent to endBy "\n".
endBy :: Eq a => [a] -> [a] -> [[a]]
-- | Split into chunks terminated by one of the given elements. Equivalent
-- to split . dropFinalBlank . dropDelims .
-- oneOf. For example:
--
--
-- endByOneOf ";," "foo;bar,baz;" == ["foo","bar","baz"]
--
endByOneOf :: Eq a => [a] -> [a] -> [[a]]
-- | Split into "words", with word boundaries indicated by the given
-- predicate. Satisfies words === wordsBy isSpace;
-- equivalent to split . dropBlanks . dropDelims
-- . whenElt. For example:
--
--
-- wordsBy (=='x') "dogxxxcatxbirdxx" == ["dog","cat","bird"]
--
wordsBy :: (a -> Bool) -> [a] -> [[a]]
-- | Split into "lines", with line boundaries indicated by the given
-- predicate. Satisfies lines === linesBy (=='n');
-- equivalent to split . dropFinalBlank .
-- dropDelims . whenElt. For example:
--
--
-- linesBy (=='x') "dogxxxcatxbirdxx" == ["dog","","","cat","bird",""]
--
linesBy :: (a -> Bool) -> [a] -> [[a]]
-- | Standard build function, specialized to building lists.
--
-- Usually build is given the rank-2 type
--
--
-- build :: (forall b. (a -> b -> b) -> b -> b) -> [a]
--
--
-- but since we only use it when (b ~ [a]), we give it the more
-- restricted type signature in order to avoid needing a non-Haskell2010
-- extension.
--
-- Note that the 0.1.4.3 release of this package did away with a custom
-- build implementation in favor of importing one from
-- GHC.Exts, which was (reportedly) faster for some applications.
-- However, in the interest of simplicity and complete Haskell2010
-- compliance as split is being included in the Haskel Platform,
-- version 0.2.1.0 has gone back to defining build manually.
-- This is in line with split's design philosophy of having
-- efficiency as a non-goal.
build :: ((a -> [a] -> [a]) -> [a] -> [a]) -> [a]
-- | chunksOf n splits a list into length-n pieces. The
-- last piece will be shorter if n does not evenly divide the
-- length of the list. If n <= 0, chunksOf n
-- l returns an infinite list of empty lists. For example:
--
-- Note that chunksOf n [] is [], not
-- [[]]. This is intentional, and is consistent with a recursive
-- definition of chunksOf; it satisfies the property that
--
--
-- chunksOf n xs ++ chunksOf n ys == chunksOf n (xs ++ ys)
--
--
-- whenever n evenly divides the length of xs.
chunksOf :: Int -> [e] -> [[e]]
-- | Split a list into chunks of the given lengths. For example:
--
--
-- splitPlaces [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
-- splitPlaces [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
-- splitPlaces [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
--
--
-- If the input list is longer than the total of the given lengths, then
-- the remaining elements are dropped. If the list is shorter than the
-- total of the given lengths, then the result may contain fewer chunks
-- than requested, and the last chunk may be shorter than requested.
splitPlaces :: Integral a => [a] -> [e] -> [[e]]
-- | Split a list into chunks of the given lengths. Unlike
-- splitPlaces, the output list will always be the same length as
-- the first input argument. If the input list is longer than the total
-- of the given lengths, then the remaining elements are dropped. If the
-- list is shorter than the total of the given lengths, then the last
-- several chunks will be shorter than requested or empty. For example:
--
--
-- splitPlacesBlanks [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
-- splitPlacesBlanks [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
-- splitPlacesBlanks [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10],[]]
--
--
-- Notice the empty list in the output of the third example, which
-- differs from the behavior of splitPlaces.
splitPlacesBlanks :: Integral a => [a] -> [e] -> [[e]]
-- | A useful recursion pattern for processing a list to produce a new
-- list, often used for "chopping" up the input list. Typically chop is
-- called with some function that will consume an initial prefix of the
-- list and produce a value and the rest of the list.
--
-- For example, many common Prelude functions can be implemented in terms
-- of chop:
--
--
-- group :: (Eq a) => [a] -> [[a]]
-- group = chop (\ xs@(x:_) -> span (==x) xs)
--
-- words :: String -> [String]
-- words = filter (not . null) . chop (span (not . isSpace) . dropWhile isSpace)
--
chop :: ([a] -> (b, [a])) -> [a] -> [b]
-- | Divides up an input list into a set of sublists, according to
-- n and m input specifications you provide. Each
-- sublist will have n items, and the start of each sublist will
-- be offset by m items from the previous one.
--
--
-- divvy 5 5 [1..20] == [[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17,18,19,20]]
--
--
-- In the case where a source list's trailing elements do no fill an
-- entire sublist, those trailing elements will be dropped.
--
--
-- divvy 5 2 [1..10] == [[1,2,3,4,5],[3,4,5,6,7],[5,6,7,8,9]]
--
--
-- As an example, you can generate a moving average over a list of
-- prices:
--
--
-- type Prices = [Float]
-- type AveragePrices = [Float]
--
-- average :: [Float] -> Float
-- average xs = sum xs / (fromIntegral $ length xs)
--
-- simpleMovingAverage :: Prices -> AveragePrices
-- simpleMovingAverage priceList =
-- map average divvyedPrices
-- where divvyedPrices = divvy 20 1 priceList
--
divvy :: Int -> Int -> [a] -> [[a]]
instance GHC.Show.Show Data.List.Split.Internals.DelimPolicy
instance GHC.Classes.Eq Data.List.Split.Internals.DelimPolicy
instance GHC.Show.Show Data.List.Split.Internals.CondensePolicy
instance GHC.Classes.Eq Data.List.Split.Internals.CondensePolicy
instance GHC.Show.Show Data.List.Split.Internals.EndPolicy
instance GHC.Classes.Eq Data.List.Split.Internals.EndPolicy
instance GHC.Classes.Eq a => GHC.Classes.Eq (Data.List.Split.Internals.Chunk a)
instance GHC.Show.Show a => GHC.Show.Show (Data.List.Split.Internals.Chunk a)
-- | The Data.List.Split module contains a wide range of strategies
-- for splitting lists with respect to some sort of delimiter, mostly
-- implemented through a unified combinator interface. The goal is to be
-- flexible yet simple. See below for usage, examples, and detailed
-- documentation of all exported functions. If you want to learn about
-- the implementation, see Data.List.Split.Internals.
--
-- A git repository containing the source (including a module with over
-- 40 QuickCheck properties) can be found at
-- https://github.com/byorgey/split.
module Data.List.Split
-- | Split on the given sublist. Equivalent to split .
-- dropDelims . onSublist. For example:
--
--
-- splitOn ".." "a..b...c....d.." == ["a","b",".c","","d",""]
--
--
-- In some parsing combinator frameworks this is also known as
-- sepBy.
--
-- Note that this is the right inverse of the intercalate function
-- from Data.List, that is,
--
--
-- intercalate x . splitOn x === id
--
--
-- splitOn x . intercalate x is the identity on
-- certain lists, but it is tricky to state the precise conditions under
-- which this holds. (For example, it is not enough to say that
-- x does not occur in any elements of the input list. Working
-- out why is left as an exercise for the reader.)
splitOn :: Eq a => [a] -> [a] -> [[a]]
-- | Split on any of the given elements. Equivalent to split .
-- dropDelims . oneOf. For example:
--
--
-- splitOneOf ";.," "foo,bar;baz.glurk" == ["foo","bar","baz","glurk"]
--
splitOneOf :: Eq a => [a] -> [a] -> [[a]]
-- | Split on elements satisfying the given predicate. Equivalent to
-- split . dropDelims . whenElt. For
-- example:
--
--
-- splitWhen (<0) [1,3,-4,5,7,-9,0,2] == [[1,3],[5,7],[0,2]]
--
splitWhen :: (a -> Bool) -> [a] -> [[a]]
-- | Split into chunks terminated by the given subsequence. Equivalent to
-- split . dropFinalBlank . dropDelims .
-- onSublist. For example:
--
--
-- endBy ";" "foo;bar;baz;" == ["foo","bar","baz"]
--
--
-- Note also that the lines function from Data.List is
-- equivalent to endBy "\n".
endBy :: Eq a => [a] -> [a] -> [[a]]
-- | Split into chunks terminated by one of the given elements. Equivalent
-- to split . dropFinalBlank . dropDelims .
-- oneOf. For example:
--
--
-- endByOneOf ";," "foo;bar,baz;" == ["foo","bar","baz"]
--
endByOneOf :: Eq a => [a] -> [a] -> [[a]]
-- | Split into "words", with word boundaries indicated by the given
-- predicate. Satisfies words === wordsBy isSpace;
-- equivalent to split . dropBlanks . dropDelims
-- . whenElt. For example:
--
--
-- wordsBy (=='x') "dogxxxcatxbirdxx" == ["dog","cat","bird"]
--
wordsBy :: (a -> Bool) -> [a] -> [[a]]
-- | Split into "lines", with line boundaries indicated by the given
-- predicate. Satisfies lines === linesBy (=='n');
-- equivalent to split . dropFinalBlank .
-- dropDelims . whenElt. For example:
--
--
-- linesBy (=='x') "dogxxxcatxbirdxx" == ["dog","","","cat","bird",""]
--
linesBy :: (a -> Bool) -> [a] -> [[a]]
-- | chunksOf n splits a list into length-n pieces. The
-- last piece will be shorter if n does not evenly divide the
-- length of the list. If n <= 0, chunksOf n
-- l returns an infinite list of empty lists. For example:
--
-- Note that chunksOf n [] is [], not
-- [[]]. This is intentional, and is consistent with a recursive
-- definition of chunksOf; it satisfies the property that
--
--
-- chunksOf n xs ++ chunksOf n ys == chunksOf n (xs ++ ys)
--
--
-- whenever n evenly divides the length of xs.
chunksOf :: Int -> [e] -> [[e]]
-- | Split a list into chunks of the given lengths. For example:
--
--
-- splitPlaces [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
-- splitPlaces [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
-- splitPlaces [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
--
--
-- If the input list is longer than the total of the given lengths, then
-- the remaining elements are dropped. If the list is shorter than the
-- total of the given lengths, then the result may contain fewer chunks
-- than requested, and the last chunk may be shorter than requested.
splitPlaces :: Integral a => [a] -> [e] -> [[e]]
-- | Split a list into chunks of the given lengths. Unlike
-- splitPlaces, the output list will always be the same length as
-- the first input argument. If the input list is longer than the total
-- of the given lengths, then the remaining elements are dropped. If the
-- list is shorter than the total of the given lengths, then the last
-- several chunks will be shorter than requested or empty. For example:
--
--
-- splitPlacesBlanks [2,3,4] [1..20] == [[1,2],[3,4,5],[6,7,8,9]]
-- splitPlacesBlanks [4,9] [1..10] == [[1,2,3,4],[5,6,7,8,9,10]]
-- splitPlacesBlanks [4,9,3] [1..10] == [[1,2,3,4],[5,6,7,8,9,10],[]]
--
--
-- Notice the empty list in the output of the third example, which
-- differs from the behavior of splitPlaces.
splitPlacesBlanks :: Integral a => [a] -> [e] -> [[e]]
-- | A useful recursion pattern for processing a list to produce a new
-- list, often used for "chopping" up the input list. Typically chop is
-- called with some function that will consume an initial prefix of the
-- list and produce a value and the rest of the list.
--
-- For example, many common Prelude functions can be implemented in terms
-- of chop:
--
--
-- group :: (Eq a) => [a] -> [[a]]
-- group = chop (\ xs@(x:_) -> span (==x) xs)
--
-- words :: String -> [String]
-- words = filter (not . null) . chop (span (not . isSpace) . dropWhile isSpace)
--
chop :: ([a] -> (b, [a])) -> [a] -> [b]
-- | Divides up an input list into a set of sublists, according to
-- n and m input specifications you provide. Each
-- sublist will have n items, and the start of each sublist will
-- be offset by m items from the previous one.
--
--
-- divvy 5 5 [1..20] == [[1,2,3,4,5],[6,7,8,9,10],[11,12,13,14,15],[16,17,18,19,20]]
--
--
-- In the case where a source list's trailing elements do no fill an
-- entire sublist, those trailing elements will be dropped.
--
--
-- divvy 5 2 [1..10] == [[1,2,3,4,5],[3,4,5,6,7],[5,6,7,8,9]]
--
--
-- As an example, you can generate a moving average over a list of
-- prices:
--
--
-- type Prices = [Float]
-- type AveragePrices = [Float]
--
-- average :: [Float] -> Float
-- average xs = sum xs / (fromIntegral $ length xs)
--
-- simpleMovingAverage :: Prices -> AveragePrices
-- simpleMovingAverage priceList =
-- map average divvyedPrices
-- where divvyedPrices = divvy 20 1 priceList
--
divvy :: Int -> Int -> [a] -> [[a]]
-- | A splitting strategy.
data Splitter a
-- | The default splitting strategy: keep delimiters in the output as
-- separate chunks, don't condense multiple consecutive delimiters into
-- one, keep initial and final blank chunks. Default delimiter is the
-- constantly false predicate.
--
-- Note that defaultSplitter should normally not be used; use
-- oneOf, onSublist, or whenElt instead, which are
-- the same as the defaultSplitter with just the delimiter
-- overridden.
--
-- The defaultSplitter strategy with any delimiter gives a
-- maximally information-preserving splitting strategy, in the sense that
-- (a) taking the concat of the output yields the original list,
-- and (b) given only the output list, we can reconstruct a
-- Splitter which would produce the same output list again given
-- the original input list. This default strategy can be overridden to
-- allow discarding various sorts of information.
defaultSplitter :: Splitter a
-- | Split a list according to the given splitting strategy. This is how to
-- "run" a Splitter that has been built using the other
-- combinators.
split :: Splitter a -> [a] -> [[a]]
-- | A splitting strategy that splits on any one of the given elements. For
-- example:
--
--
-- split (oneOf "xyz") "aazbxyzcxd" == ["aa","z","b","x","","y","","z","c","x","d"]
--
oneOf :: Eq a => [a] -> Splitter a
-- | A splitting strategy that splits on the given list, when it is
-- encountered as an exact subsequence. For example:
--
--
-- split (onSublist "xyz") "aazbxyzcxd" == ["aazb","xyz","cxd"]
--
--
-- Note that splitting on the empty list is a special case, which splits
-- just before every element of the list being split. For example:
--
--
-- split (onSublist "") "abc" == ["","","a","","b","","c"]
-- split (dropDelims . dropBlanks $ onSublist "") "abc" == ["a","b","c"]
--
--
-- However, if you want to break a list into singleton elements like
-- this, you are better off using chunksOf 1, or better
-- yet, map (:[]).
onSublist :: Eq a => [a] -> Splitter a
-- | A splitting strategy that splits on any elements that satisfy the
-- given predicate. For example:
--
--
-- split (whenElt (<0)) [2,4,-3,6,-9,1] == [[2,4],[-3],[6],[-9],[1]]
--
whenElt :: (a -> Bool) -> Splitter a
-- | Drop delimiters from the output (the default is to keep them). For
-- example,
--
--
-- split (oneOf ":") "a:b:c" == ["a", ":", "b", ":", "c"]
-- split (dropDelims $ oneOf ":") "a:b:c" == ["a", "b", "c"]
--
dropDelims :: Splitter a -> Splitter a
-- | Keep delimiters in the output by prepending them to adjacent chunks.
-- For example:
--
--
-- split (keepDelimsL $ oneOf "xyz") "aazbxyzcxd" == ["aa","zb","x","y","zc","xd"]
--
keepDelimsL :: Splitter a -> Splitter a
-- | Keep delimiters in the output by appending them to adjacent chunks.
-- For example:
--
--
-- split (keepDelimsR $ oneOf "xyz") "aazbxyzcxd" == ["aaz","bx","y","z","cx","d"]
--
keepDelimsR :: Splitter a -> Splitter a
-- | Condense multiple consecutive delimiters into one. For example:
--
--
-- split (condense $ oneOf "xyz") "aazbxyzcxd" == ["aa","z","b","xyz","c","x","d"]
-- split (dropDelims $ oneOf "xyz") "aazbxyzcxd" == ["aa","b","","","c","d"]
-- split (condense . dropDelims $ oneOf "xyz") "aazbxyzcxd" == ["aa","b","c","d"]
--
condense :: Splitter a -> Splitter a
-- | Don't generate a blank chunk if there is a delimiter at the beginning.
-- For example:
--
--
-- split (oneOf ":") ":a:b" == ["",":","a",":","b"]
-- split (dropInitBlank $ oneOf ":") ":a:b" == [":","a",":","b"]
--
dropInitBlank :: Splitter a -> Splitter a
-- | Don't generate a blank chunk if there is a delimiter at the end. For
-- example:
--
--
-- split (oneOf ":") "a:b:" == ["a",":","b",":",""]
-- split (dropFinalBlank $ oneOf ":") "a:b:" == ["a",":","b",":"]
--
dropFinalBlank :: Splitter a -> Splitter a
-- | Don't generate blank chunks between consecutive delimiters. For
-- example:
--
--
-- split (oneOf ":") "::b:::a" == ["",":","",":","b",":","",":","",":","a"]
-- split (dropInnerBlanks $ oneOf ":") "::b:::a" == ["", ":",":","b",":",":",":","a"]
--
dropInnerBlanks :: Splitter a -> Splitter a
-- | Drop all blank chunks from the output, and condense consecutive
-- delimiters into one. Equivalent to dropInitBlank .
-- dropFinalBlank . condense. For example:
--
--
-- split (oneOf ":") "::b:::a" == ["",":","",":","b",":","",":","",":","a"]
-- split (dropBlanks $ oneOf ":") "::b:::a" == ["::","b",":::","a"]
--
dropBlanks :: Splitter a -> Splitter a
-- | Make a strategy that splits a list into chunks that all start with the
-- given subsequence (except possibly the first). Equivalent to
-- dropInitBlank . keepDelimsL . onSublist.
-- For example:
--
--
-- split (startsWith "app") "applyapplicativeapplaudapproachapple" == ["apply","applicative","applaud","approach","apple"]
--
startsWith :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all start with one
-- of the given elements (except possibly the first). Equivalent to
-- dropInitBlank . keepDelimsL . oneOf. For
-- example:
--
--
-- split (startsWithOneOf ['A'..'Z']) "ACamelCaseIdentifier" == ["A","Camel","Case","Identifier"]
--
startsWithOneOf :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all end with the
-- given subsequence, except possibly the last. Equivalent to
-- dropFinalBlank . keepDelimsR .
-- onSublist. For example:
--
--
-- split (endsWith "ly") "happilyslowlygnarlylily" == ["happily","slowly","gnarly","lily"]
--
endsWith :: Eq a => [a] -> Splitter a
-- | Make a strategy that splits a list into chunks that all end with one
-- of the given elements, except possibly the last. Equivalent to
-- dropFinalBlank . keepDelimsR . oneOf.
-- For example:
--
--
-- split (condense $ endsWithOneOf ".,?! ") "Hi, there! How are you?" == ["Hi, ","there! ","How ","are ","you?"]
--
endsWithOneOf :: Eq a => [a] -> Splitter a