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{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE BangPatterns, CPP, MagicHash #-}
-- |
-- Module : Data.Text.Lazy
-- Copyright : (c) 2009, 2010 Bryan O'Sullivan
--
-- License : BSD-style
-- Maintainer : bos@serpentine.com, rtomharper@googlemail.com,
-- duncan@haskell.org
-- Stability : experimental
-- Portability : GHC
--
-- A time and space-efficient implementation of Unicode text using
-- lists of packed arrays.
--
-- /Note/: Read below the synopsis for important notes on the use of
-- this module.
--
-- The representation used by this module is suitable for high
-- performance use and for streaming large quantities of data. It
-- provides a means to manipulate a large body of text without
-- requiring that the entire content be resident in memory.
--
-- Some operations, such as 'concat', 'append', 'reverse' and 'cons',
-- have better time complexity than their "Data.Text" equivalents, due
-- to the underlying representation being a list of chunks. For other
-- operations, lazy 'Text's are usually within a few percent of strict
-- ones, but often with better heap usage if used in a streaming
-- fashion. For data larger than available memory, or if you have
-- tight memory constraints, this module will be the only option.
--
-- This module is intended to be imported @qualified@, to avoid name
-- clashes with "Prelude" functions. eg.
--
-- > import qualified Data.Text.Lazy as L
module Data.Text.Lazy
(
-- * Fusion
-- $fusion
-- * Acceptable data
-- $replacement
-- * Types
Text
-- * Creation and elimination
, pack
, unpack
, singleton
, empty
, fromChunks
, toChunks
, toStrict
, fromStrict
, foldrChunks
, foldlChunks
-- * Basic interface
, cons
, snoc
, append
, uncons
, head
, last
, tail
, init
, null
, length
, compareLength
-- * Transformations
, map
, intercalate
, intersperse
, transpose
, reverse
, replace
-- ** Case conversion
-- $case
, toCaseFold
, toLower
, toUpper
-- ** Justification
, justifyLeft
, justifyRight
, center
-- * Folds
, foldl
, foldl'
, foldl1
, foldl1'
, foldr
, foldr1
-- ** Special folds
, concat
, concatMap
, any
, all
, maximum
, minimum
-- * Construction
-- ** Scans
, scanl
, scanl1
, scanr
, scanr1
-- ** Accumulating maps
, mapAccumL
, mapAccumR
-- ** Generation and unfolding
, replicate
, unfoldr
, unfoldrN
-- * Substrings
-- ** Breaking strings
, take
, drop
, takeWhile
, dropWhile
, dropWhileEnd
, dropAround
, strip
, stripStart
, stripEnd
, splitAt
, span
, breakOn
, breakOnEnd
, break
, group
, groupBy
, inits
, tails
-- ** Breaking into many substrings
-- $split
, splitOn
, split
, chunksOf
-- , breakSubstring
-- ** Breaking into lines and words
, lines
, words
, unlines
, unwords
-- * Predicates
, isPrefixOf
, isSuffixOf
, isInfixOf
-- ** View patterns
, stripPrefix
, stripSuffix
, commonPrefixes
-- * Searching
, filter
, find
, breakOnAll
, partition
-- , findSubstring
-- * Indexing
, index
, count
-- * Zipping and unzipping
, zip
, zipWith
-- -* Ordered text
-- , sort
) where
import Prelude (Char, Bool(..), Maybe(..), String,
Eq(..), Ord(..), Ordering(..), Read(..), Show(..),
(&&), (||), (+), (-), (.), ($), (++),
div, error, flip, fmap, fromIntegral, not, otherwise)
import qualified Prelude as P
#if defined(HAVE_DEEPSEQ)
import Control.DeepSeq (NFData(..))
#endif
import qualified Data.ByteString.Lazy as B (fromChunks)
import Data.ByteString.Unsafe (unsafePackAddress)
import Data.Int (Int64)
import qualified Data.List as L
import Data.Char (isSpace)
import Data.Data (Data(gfoldl, toConstr, gunfold, dataTypeOf))
#if __GLASGOW_HASKELL__ >= 612
import Data.Data (mkNoRepType)
#else
import Data.Data (mkNorepType)
#endif
import Data.Monoid (Monoid(..))
import Data.String (IsString(..))
import qualified Data.Text as T
import qualified Data.Text.Internal as T
import qualified Data.Text.Fusion.Common as S
import qualified Data.Text.Unsafe as T
import qualified Data.Text.Lazy.Fusion as S
import Data.Text.Fusion.Internal (PairS(..))
import Data.Text.Lazy.Encoding (decodeUtf8)
import Data.Text.Lazy.Fusion (stream, unstream)
import Data.Text.Lazy.Internal (Text(..), chunk, empty, foldlChunks, foldrChunks)
import Data.Text.Internal (firstf, safe, textP)
import qualified Data.Text.Util as U
import Data.Text.Lazy.Search (indices)
import GHC.CString
import GHC.Prim
-- $fusion
--
-- Most of the functions in this module are subject to /fusion/,
-- meaning that a pipeline of such functions will usually allocate at
-- most one 'Text' value.
--
-- As an example, consider the following pipeline:
--
-- > import Data.Text.Lazy as T
-- > import Data.Text.Lazy.Encoding as E
-- > import Data.ByteString.Lazy (ByteString)
-- >
-- > countChars :: ByteString -> Int
-- > countChars = T.length . T.toUpper . E.decodeUtf8
--
-- From the type signatures involved, this looks like it should
-- allocate one 'ByteString' value, and two 'Text' values. However,
-- when a module is compiled with optimisation enabled under GHC, the
-- two intermediate 'Text' values will be optimised away, and the
-- function will be compiled down to a single loop over the source
-- 'ByteString'.
--
-- Functions that can be fused by the compiler are documented with the
-- phrase \"Subject to fusion\".
-- $replacement
--
-- A 'Text' value is a sequence of Unicode scalar values, as defined
-- in §3.9, definition D76 of the Unicode 5.2 standard:
-- <http://www.unicode.org/versions/Unicode5.2.0/ch03.pdf#page=35>. As
-- such, a 'Text' cannot contain values in the range U+D800 to U+DFFF
-- inclusive. Haskell implementations admit all Unicode code points
-- (&#xa7;3.4, definition D10) as 'Char' values, including code points
-- from this invalid range. This means that there are some 'Char'
-- values that are not valid Unicode scalar values, and the functions
-- in this module must handle those cases.
--
-- Within this module, many functions construct a 'Text' from one or
-- more 'Char' values. Those functions will substitute 'Char' values
-- that are not valid Unicode scalar values with the replacement
-- character \"&#xfffd;\" (U+FFFD). Functions that perform this
-- inspection and replacement are documented with the phrase
-- \"Performs replacement on invalid scalar values\".
--
-- (One reason for this policy of replacement is that internally, a
-- 'Text' value is represented as packed UTF-16 data. Values in the
-- range U+D800 through U+DFFF are used by UTF-16 to denote surrogate
-- code points, and so cannot be represented. The functions replace
-- invalid scalar values, instead of dropping them, as a security
-- measure. For details, see Unicode Technical Report 36, &#xa7;3.5:
-- <http://unicode.org/reports/tr36#Deletion_of_Noncharacters>)
equal :: Text -> Text -> Bool
equal Empty Empty = True
equal Empty _ = False
equal _ Empty = False
equal (Chunk a as) (Chunk b bs) =
case compare lenA lenB of
LT -> a == (T.takeWord16 lenA b) &&
as `equal` Chunk (T.dropWord16 lenA b) bs
EQ -> a == b && as `equal` bs
GT -> T.takeWord16 lenB a == b &&
Chunk (T.dropWord16 lenB a) as `equal` bs
where lenA = T.lengthWord16 a
lenB = T.lengthWord16 b
instance Eq Text where
(==) = equal
{-# INLINE (==) #-}
instance Ord Text where
compare = compareText
compareText :: Text -> Text -> Ordering
compareText Empty Empty = EQ
compareText Empty _ = LT
compareText _ Empty = GT
compareText (Chunk a0 as) (Chunk b0 bs) = outer a0 b0
where
outer ta@(T.Text arrA offA lenA) tb@(T.Text arrB offB lenB) = go 0 0
where
go !i !j
| i >= lenA = compareText as (chunk (T.Text arrB (offB+j) (lenB-j)) bs)
| j >= lenB = compareText (chunk (T.Text arrA (offA+i) (lenA-i)) as) bs
| a < b = LT
| a > b = GT
| otherwise = go (i+di) (j+dj)
where T.Iter a di = T.iter ta i
T.Iter b dj = T.iter tb j
instance Show Text where
showsPrec p ps r = showsPrec p (unpack ps) r
instance Read Text where
readsPrec p str = [(pack x,y) | (x,y) <- readsPrec p str]
instance Monoid Text where
mempty = empty
mappend = append
mconcat = concat
instance IsString Text where
fromString = pack
textLiteral# :: Addr# -> Text
textLiteral# addr# = T.inlinePerformIO $ do
bytesStrict <- unsafePackAddress addr#
let bytesLazy = B.fromChunks [bytesStrict]
P.return $ decodeUtf8 bytesLazy
{-# RULES "Overloaded literal strings" forall s. unstream (S.streamList (P.map safe (unpackCString# s))) = textLiteral# s #-}
{-# RULES "Overloaded literal strings utf8" forall s. unstream (S.streamList (P.map safe (unpackCStringUtf8# s))) = textLiteral# s #-}
#if defined(HAVE_DEEPSEQ)
instance NFData Text where
rnf Empty = ()
rnf (Chunk _ ts) = rnf ts
#endif
instance Data Text where
gfoldl f z txt = z pack `f` (unpack txt)
toConstr _ = error "Data.Text.Lazy.Text.toConstr"
gunfold _ _ = error "Data.Text.Lazy.Text.gunfold"
#if __GLASGOW_HASKELL__ >= 612
dataTypeOf _ = mkNoRepType "Data.Text.Lazy.Text"
#else
dataTypeOf _ = mkNorepType "Data.Text.Lazy.Text"
#endif
-- | /O(n)/ Convert a 'String' into a 'Text'.
--
-- Subject to fusion. Performs replacement on invalid scalar values.
pack :: String -> Text
pack = unstream . S.streamList . L.map safe
{-# INLINE [1] pack #-}
-- | /O(n)/ Convert a 'Text' into a 'String'.
-- Subject to fusion.
unpack :: Text -> String
unpack t = S.unstreamList (stream t)
{-# INLINE [1] unpack #-}
-- | /O(1)/ Convert a character into a Text. Subject to fusion.
-- Performs replacement on invalid scalar values.
singleton :: Char -> Text
singleton c = Chunk (T.singleton c) Empty
{-# INLINE [1] singleton #-}
{-# RULES
"LAZY TEXT singleton -> fused" [~1] forall c.
singleton c = unstream (S.singleton c)
"LAZY TEXT singleton -> unfused" [1] forall c.
unstream (S.singleton c) = singleton c
#-}
-- | /O(c)/ Convert a list of strict 'T.Text's into a lazy 'Text'.
fromChunks :: [T.Text] -> Text
fromChunks cs = L.foldr chunk Empty cs
-- | /O(n)/ Convert a lazy 'Text' into a list of strict 'T.Text's.
toChunks :: Text -> [T.Text]
toChunks cs = foldrChunks (:) [] cs
-- | /O(n)/ Convert a lazy 'Text' into a strict 'T.Text'.
toStrict :: Text -> T.Text
toStrict t = T.concat (toChunks t)
{-# INLINE [1] toStrict #-}
-- | /O(c)/ Convert a strict 'T.Text' into a lazy 'Text'.
fromStrict :: T.Text -> Text
fromStrict t = chunk t Empty
{-# INLINE [1] fromStrict #-}
-- -----------------------------------------------------------------------------
-- * Basic functions
-- | /O(n)/ Adds a character to the front of a 'Text'. This function
-- is more costly than its 'List' counterpart because it requires
-- copying a new array. Subject to fusion.
cons :: Char -> Text -> Text
cons c t = Chunk (T.singleton c) t
{-# INLINE [1] cons #-}
infixr 5 `cons`
{-# RULES
"LAZY TEXT cons -> fused" [~1] forall c t.
cons c t = unstream (S.cons c (stream t))
"LAZY TEXT cons -> unfused" [1] forall c t.
unstream (S.cons c (stream t)) = cons c t
#-}
-- | /O(n)/ Adds a character to the end of a 'Text'. This copies the
-- entire array in the process, unless fused. Subject to fusion.
snoc :: Text -> Char -> Text
snoc t c = foldrChunks Chunk (singleton c) t
{-# INLINE [1] snoc #-}
{-# RULES
"LAZY TEXT snoc -> fused" [~1] forall t c.
snoc t c = unstream (S.snoc (stream t) c)
"LAZY TEXT snoc -> unfused" [1] forall t c.
unstream (S.snoc (stream t) c) = snoc t c
#-}
-- | /O(n\/c)/ Appends one 'Text' to another. Subject to fusion.
append :: Text -> Text -> Text
append xs ys = foldrChunks Chunk ys xs
{-# INLINE [1] append #-}
{-# RULES
"LAZY TEXT append -> fused" [~1] forall t1 t2.
append t1 t2 = unstream (S.append (stream t1) (stream t2))
"LAZY TEXT append -> unfused" [1] forall t1 t2.
unstream (S.append (stream t1) (stream t2)) = append t1 t2
#-}
-- | /O(1)/ Returns the first character and rest of a 'Text', or
-- 'Nothing' if empty. Subject to fusion.
uncons :: Text -> Maybe (Char, Text)
uncons Empty = Nothing
uncons (Chunk t ts) = Just (T.unsafeHead t, ts')
where ts' | T.compareLength t 1 == EQ = ts
| otherwise = Chunk (T.unsafeTail t) ts
{-# INLINE uncons #-}
-- | /O(1)/ Returns the first character of a 'Text', which must be
-- non-empty. Subject to fusion.
head :: Text -> Char
head t = S.head (stream t)
{-# INLINE head #-}
-- | /O(1)/ Returns all characters after the head of a 'Text', which
-- must be non-empty. Subject to fusion.
tail :: Text -> Text
tail (Chunk t ts) = chunk (T.tail t) ts
tail Empty = emptyError "tail"
{-# INLINE [1] tail #-}
{-# RULES
"LAZY TEXT tail -> fused" [~1] forall t.
tail t = unstream (S.tail (stream t))
"LAZY TEXT tail -> unfused" [1] forall t.
unstream (S.tail (stream t)) = tail t
#-}
-- | /O(1)/ Returns all but the last character of a 'Text', which must
-- be non-empty. Subject to fusion.
init :: Text -> Text
init (Chunk t0 ts0) = go t0 ts0
where go t (Chunk t' ts) = Chunk t (go t' ts)
go t Empty = chunk (T.init t) Empty
init Empty = emptyError "init"
{-# INLINE [1] init #-}
{-# RULES
"LAZY TEXT init -> fused" [~1] forall t.
init t = unstream (S.init (stream t))
"LAZY TEXT init -> unfused" [1] forall t.
unstream (S.init (stream t)) = init t
#-}
-- | /O(1)/ Tests whether a 'Text' is empty or not. Subject to
-- fusion.
null :: Text -> Bool
null Empty = True
null _ = False
{-# INLINE [1] null #-}
{-# RULES
"LAZY TEXT null -> fused" [~1] forall t.
null t = S.null (stream t)
"LAZY TEXT null -> unfused" [1] forall t.
S.null (stream t) = null t
#-}
-- | /O(1)/ Tests whether a 'Text' contains exactly one character.
-- Subject to fusion.
isSingleton :: Text -> Bool
isSingleton = S.isSingleton . stream
{-# INLINE isSingleton #-}
-- | /O(1)/ Returns the last character of a 'Text', which must be
-- non-empty. Subject to fusion.
last :: Text -> Char
last Empty = emptyError "last"
last (Chunk t ts) = go t ts
where go _ (Chunk t' ts') = go t' ts'
go t' Empty = T.last t'
{-# INLINE [1] last #-}
{-# RULES
"LAZY TEXT last -> fused" [~1] forall t.
last t = S.last (stream t)
"LAZY TEXT last -> unfused" [1] forall t.
S.last (stream t) = last t
#-}
-- | /O(n)/ Returns the number of characters in a 'Text'.
-- Subject to fusion.
length :: Text -> Int64
length = foldlChunks go 0
where go l t = l + fromIntegral (T.length t)
{-# INLINE [1] length #-}
{-# RULES
"LAZY TEXT length -> fused" [~1] forall t.
length t = S.length (stream t)
"LAZY TEXT length -> unfused" [1] forall t.
S.length (stream t) = length t
#-}
-- | /O(n)/ Compare the count of characters in a 'Text' to a number.
-- Subject to fusion.
--
-- This function gives the same answer as comparing against the result
-- of 'length', but can short circuit if the count of characters is
-- greater than the number, and hence be more efficient.
compareLength :: Text -> Int64 -> Ordering
compareLength t n = S.compareLengthI (stream t) n
{-# INLINE [1] compareLength #-}
-- We don't apply those otherwise appealing length-to-compareLength
-- rewrite rules here, because they can change the strictness
-- properties of code.
-- | /O(n)/ 'map' @f@ @t@ is the 'Text' obtained by applying @f@ to
-- each element of @t@. Subject to fusion. Performs replacement on
-- invalid scalar values.
map :: (Char -> Char) -> Text -> Text
map f t = unstream (S.map (safe . f) (stream t))
{-# INLINE [1] map #-}
-- | /O(n)/ The 'intercalate' function takes a 'Text' and a list of
-- 'Text's and concatenates the list after interspersing the first
-- argument between each element of the list.
intercalate :: Text -> [Text] -> Text
intercalate t = concat . (U.intersperse t)
{-# INLINE intercalate #-}
-- | /O(n)/ The 'intersperse' function takes a character and places it
-- between the characters of a 'Text'. Subject to fusion. Performs
-- replacement on invalid scalar values.
intersperse :: Char -> Text -> Text
intersperse c t = unstream (S.intersperse (safe c) (stream t))
{-# INLINE intersperse #-}
-- | /O(n)/ Left-justify a string to the given length, using the
-- specified fill character on the right. Subject to fusion. Performs
-- replacement on invalid scalar values.
--
-- Examples:
--
-- > justifyLeft 7 'x' "foo" == "fooxxxx"
-- > justifyLeft 3 'x' "foobar" == "foobar"
justifyLeft :: Int64 -> Char -> Text -> Text
justifyLeft k c t
| len >= k = t
| otherwise = t `append` replicateChar (k-len) c
where len = length t
{-# INLINE [1] justifyLeft #-}
{-# RULES
"LAZY TEXT justifyLeft -> fused" [~1] forall k c t.
justifyLeft k c t = unstream (S.justifyLeftI k c (stream t))
"LAZY TEXT justifyLeft -> unfused" [1] forall k c t.
unstream (S.justifyLeftI k c (stream t)) = justifyLeft k c t
#-}
-- | /O(n)/ Right-justify a string to the given length, using the
-- specified fill character on the left. Performs replacement on
-- invalid scalar values.
--
-- Examples:
--
-- > justifyRight 7 'x' "bar" == "xxxxbar"
-- > justifyRight 3 'x' "foobar" == "foobar"
justifyRight :: Int64 -> Char -> Text -> Text
justifyRight k c t
| len >= k = t
| otherwise = replicateChar (k-len) c `append` t
where len = length t
{-# INLINE justifyRight #-}
-- | /O(n)/ Center a string to the given length, using the specified
-- fill character on either side. Performs replacement on invalid
-- scalar values.
--
-- Examples:
--
-- > center 8 'x' "HS" = "xxxHSxxx"
center :: Int64 -> Char -> Text -> Text
center k c t
| len >= k = t
| otherwise = replicateChar l c `append` t `append` replicateChar r c
where len = length t
d = k - len
r = d `div` 2
l = d - r
{-# INLINE center #-}
-- | /O(n)/ The 'transpose' function transposes the rows and columns
-- of its 'Text' argument. Note that this function uses 'pack',
-- 'unpack', and the list version of transpose, and is thus not very
-- efficient.
transpose :: [Text] -> [Text]
transpose ts = L.map (\ss -> Chunk (T.pack ss) Empty)
(L.transpose (L.map unpack ts))
-- TODO: make this fast
-- | /O(n)/ 'reverse' @t@ returns the elements of @t@ in reverse order.
reverse :: Text -> Text
reverse = rev Empty
where rev a Empty = a
rev a (Chunk t ts) = rev (Chunk (T.reverse t) a) ts
-- | /O(m+n)/ Replace every occurrence of one substring with another.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
replace :: Text -- ^ Text to search for
-> Text -- ^ Replacement text
-> Text -- ^ Input text
-> Text
replace s d = intercalate d . splitOn s
{-# INLINE replace #-}
-- ----------------------------------------------------------------------------
-- ** Case conversions (folds)
-- $case
--
-- With Unicode text, it is incorrect to use combinators like @map
-- toUpper@ to case convert each character of a string individually.
-- Instead, use the whole-string case conversion functions from this
-- module. For correctness in different writing systems, these
-- functions may map one input character to two or three output
-- characters.
-- | /O(n)/ Convert a string to folded case. This function is mainly
-- useful for performing caseless (or case insensitive) string
-- comparisons.
--
-- A string @x@ is a caseless match for a string @y@ if and only if:
--
-- @toCaseFold x == toCaseFold y@
--
-- The result string may be longer than the input string, and may
-- differ from applying 'toLower' to the input string. For instance,
-- the Armenian small ligature men now (U+FB13) is case folded to the
-- bigram men now (U+0574 U+0576), while the micro sign (U+00B5) is
-- case folded to the Greek small letter letter mu (U+03BC) instead of
-- itself.
toCaseFold :: Text -> Text
toCaseFold t = unstream (S.toCaseFold (stream t))
{-# INLINE [0] toCaseFold #-}
-- | /O(n)/ Convert a string to lower case, using simple case
-- conversion. The result string may be longer than the input string.
-- For instance, the Latin capital letter I with dot above (U+0130)
-- maps to the sequence Latin small letter i (U+0069) followed by
-- combining dot above (U+0307).
toLower :: Text -> Text
toLower t = unstream (S.toLower (stream t))
{-# INLINE toLower #-}
-- | /O(n)/ Convert a string to upper case, using simple case
-- conversion. The result string may be longer than the input string.
-- For instance, the German eszett (U+00DF) maps to the two-letter
-- sequence SS.
toUpper :: Text -> Text
toUpper t = unstream (S.toUpper (stream t))
{-# INLINE toUpper #-}
-- | /O(n)/ 'foldl', applied to a binary operator, a starting value
-- (typically the left-identity of the operator), and a 'Text',
-- reduces the 'Text' using the binary operator, from left to right.
-- Subject to fusion.
foldl :: (a -> Char -> a) -> a -> Text -> a
foldl f z t = S.foldl f z (stream t)
{-# INLINE foldl #-}
-- | /O(n)/ A strict version of 'foldl'.
-- Subject to fusion.
foldl' :: (a -> Char -> a) -> a -> Text -> a
foldl' f z t = S.foldl' f z (stream t)
{-# INLINE foldl' #-}
-- | /O(n)/ A variant of 'foldl' that has no starting value argument,
-- and thus must be applied to a non-empty 'Text'. Subject to fusion.
foldl1 :: (Char -> Char -> Char) -> Text -> Char
foldl1 f t = S.foldl1 f (stream t)
{-# INLINE foldl1 #-}
-- | /O(n)/ A strict version of 'foldl1'. Subject to fusion.
foldl1' :: (Char -> Char -> Char) -> Text -> Char
foldl1' f t = S.foldl1' f (stream t)
{-# INLINE foldl1' #-}
-- | /O(n)/ 'foldr', applied to a binary operator, a starting value
-- (typically the right-identity of the operator), and a 'Text',
-- reduces the 'Text' using the binary operator, from right to left.
-- Subject to fusion.
foldr :: (Char -> a -> a) -> a -> Text -> a
foldr f z t = S.foldr f z (stream t)
{-# INLINE foldr #-}
-- | /O(n)/ A variant of 'foldr' that has no starting value argument,
-- and thus must be applied to a non-empty 'Text'. Subject to
-- fusion.
foldr1 :: (Char -> Char -> Char) -> Text -> Char
foldr1 f t = S.foldr1 f (stream t)
{-# INLINE foldr1 #-}
-- | /O(n)/ Concatenate a list of 'Text's.
concat :: [Text] -> Text
concat = to
where
go Empty css = to css
go (Chunk c cs) css = Chunk c (go cs css)
to [] = Empty
to (cs:css) = go cs css
{-# INLINE concat #-}
-- | /O(n)/ Map a function over a 'Text' that results in a 'Text', and
-- concatenate the results.
concatMap :: (Char -> Text) -> Text -> Text
concatMap f = concat . foldr ((:) . f) []
{-# INLINE concatMap #-}
-- | /O(n)/ 'any' @p@ @t@ determines whether any character in the
-- 'Text' @t@ satisifes the predicate @p@. Subject to fusion.
any :: (Char -> Bool) -> Text -> Bool
any p t = S.any p (stream t)
{-# INLINE any #-}
-- | /O(n)/ 'all' @p@ @t@ determines whether all characters in the
-- 'Text' @t@ satisify the predicate @p@. Subject to fusion.
all :: (Char -> Bool) -> Text -> Bool
all p t = S.all p (stream t)
{-# INLINE all #-}
-- | /O(n)/ 'maximum' returns the maximum value from a 'Text', which
-- must be non-empty. Subject to fusion.
maximum :: Text -> Char
maximum t = S.maximum (stream t)
{-# INLINE maximum #-}
-- | /O(n)/ 'minimum' returns the minimum value from a 'Text', which
-- must be non-empty. Subject to fusion.
minimum :: Text -> Char
minimum t = S.minimum (stream t)
{-# INLINE minimum #-}
-- | /O(n)/ 'scanl' is similar to 'foldl', but returns a list of
-- successive reduced values from the left. Subject to fusion.
-- Performs replacement on invalid scalar values.
--
-- > scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
--
-- Note that
--
-- > last (scanl f z xs) == foldl f z xs.
scanl :: (Char -> Char -> Char) -> Char -> Text -> Text
scanl f z t = unstream (S.scanl g z (stream t))
where g a b = safe (f a b)
{-# INLINE scanl #-}
-- | /O(n)/ 'scanl1' is a variant of 'scanl' that has no starting
-- value argument. Subject to fusion. Performs replacement on
-- invalid scalar values.
--
-- > scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
scanl1 :: (Char -> Char -> Char) -> Text -> Text
scanl1 f t0 = case uncons t0 of
Nothing -> empty
Just (t,ts) -> scanl f t ts
{-# INLINE scanl1 #-}
-- | /O(n)/ 'scanr' is the right-to-left dual of 'scanl'. Performs
-- replacement on invalid scalar values.
--
-- > scanr f v == reverse . scanl (flip f) v . reverse
scanr :: (Char -> Char -> Char) -> Char -> Text -> Text
scanr f v = reverse . scanl g v . reverse
where g a b = safe (f b a)
-- | /O(n)/ 'scanr1' is a variant of 'scanr' that has no starting
-- value argument. Performs replacement on invalid scalar values.
scanr1 :: (Char -> Char -> Char) -> Text -> Text
scanr1 f t | null t = empty
| otherwise = scanr f (last t) (init t)
-- | /O(n)/ Like a combination of 'map' and 'foldl''. Applies a
-- function to each element of a 'Text', passing an accumulating
-- parameter from left to right, and returns a final 'Text'. Performs
-- replacement on invalid scalar values.
mapAccumL :: (a -> Char -> (a,Char)) -> a -> Text -> (a, Text)
mapAccumL f = go
where
go z (Chunk c cs) = (z'', Chunk c' cs')
where (z', c') = T.mapAccumL f z c
(z'', cs') = go z' cs
go z Empty = (z, Empty)
{-# INLINE mapAccumL #-}
-- | The 'mapAccumR' function behaves like a combination of 'map' and
-- a strict 'foldr'; it applies a function to each element of a
-- 'Text', passing an accumulating parameter from right to left, and
-- returning a final value of this accumulator together with the new
-- 'Text'. Performs replacement on invalid scalar values.
mapAccumR :: (a -> Char -> (a,Char)) -> a -> Text -> (a, Text)
mapAccumR f = go
where
go z (Chunk c cs) = (z'', Chunk c' cs')
where (z'', c') = T.mapAccumR f z' c
(z', cs') = go z cs
go z Empty = (z, Empty)
{-# INLINE mapAccumR #-}
-- | /O(n*m)/ 'replicate' @n@ @t@ is a 'Text' consisting of the input
-- @t@ repeated @n@ times.
replicate :: Int64 -> Text -> Text
replicate n t
| null t || n <= 0 = empty
| isSingleton t = replicateChar n (head t)
| otherwise = concat (rep 0)
where rep !i | i >= n = []
| otherwise = t : rep (i+1)
{-# INLINE replicate #-}
-- | /O(n)/ 'replicateChar' @n@ @c@ is a 'Text' of length @n@ with @c@ the
-- value of every element. Subject to fusion.
replicateChar :: Int64 -> Char -> Text
replicateChar n c = unstream (S.replicateCharI n (safe c))
{-# INLINE replicateChar #-}
{-# RULES
"LAZY TEXT replicate/singleton -> replicateChar" [~1] forall n c.
replicate n (singleton c) = replicateChar n c
#-}
-- | /O(n)/, where @n@ is the length of the result. The 'unfoldr'
-- function is analogous to the List 'L.unfoldr'. 'unfoldr' builds a
-- 'Text' from a seed value. The function takes the element and
-- returns 'Nothing' if it is done producing the 'Text', otherwise
-- 'Just' @(a,b)@. In this case, @a@ is the next 'Char' in the
-- string, and @b@ is the seed value for further production. Performs
-- replacement on invalid scalar values.
unfoldr :: (a -> Maybe (Char,a)) -> a -> Text
unfoldr f s = unstream (S.unfoldr (firstf safe . f) s)
{-# INLINE unfoldr #-}
-- | /O(n)/ Like 'unfoldr', 'unfoldrN' builds a 'Text' from a seed
-- value. However, the length of the result should be limited by the
-- first argument to 'unfoldrN'. This function is more efficient than
-- 'unfoldr' when the maximum length of the result is known and
-- correct, otherwise its performance is similar to 'unfoldr'.
-- Performs replacement on invalid scalar values.
unfoldrN :: Int64 -> (a -> Maybe (Char,a)) -> a -> Text
unfoldrN n f s = unstream (S.unfoldrN n (firstf safe . f) s)
{-# INLINE unfoldrN #-}
-- | /O(n)/ 'take' @n@, applied to a 'Text', returns the prefix of the
-- 'Text' of length @n@, or the 'Text' itself if @n@ is greater than
-- the length of the Text. Subject to fusion.
take :: Int64 -> Text -> Text
take i _ | i <= 0 = Empty
take i t0 = take' i t0
where take' 0 _ = Empty
take' _ Empty = Empty
take' n (Chunk t ts)
| n < len = Chunk (T.take (fromIntegral n) t) Empty
| otherwise = Chunk t (take' (n - len) ts)
where len = fromIntegral (T.length t)
{-# INLINE [1] take #-}
{-# RULES
"LAZY TEXT take -> fused" [~1] forall n t.
take n t = unstream (S.take n (stream t))
"LAZY TEXT take -> unfused" [1] forall n t.
unstream (S.take n (stream t)) = take n t
#-}
-- | /O(n)/ 'drop' @n@, applied to a 'Text', returns the suffix of the
-- 'Text' after the first @n@ characters, or the empty 'Text' if @n@
-- is greater than the length of the 'Text'. Subject to fusion.
drop :: Int64 -> Text -> Text
drop i t0
| i <= 0 = t0
| otherwise = drop' i t0
where drop' 0 ts = ts
drop' _ Empty = Empty
drop' n (Chunk t ts)
| n < len = Chunk (T.drop (fromIntegral n) t) ts
| otherwise = drop' (n - len) ts
where len = fromIntegral (T.length t)
{-# INLINE [1] drop #-}
{-# RULES
"LAZY TEXT drop -> fused" [~1] forall n t.
drop n t = unstream (S.drop n (stream t))
"LAZY TEXT drop -> unfused" [1] forall n t.
unstream (S.drop n (stream t)) = drop n t
#-}
-- | /O(n)/ 'dropWords' @n@ returns the suffix with @n@ 'Word16'
-- values dropped, or the empty 'Text' if @n@ is greater than the
-- number of 'Word16' values present.
dropWords :: Int64 -> Text -> Text
dropWords i t0
| i <= 0 = t0
| otherwise = drop' i t0
where drop' 0 ts = ts
drop' _ Empty = Empty
drop' n (Chunk (T.Text arr off len) ts)
| n < len' = chunk (textP arr (off+n') (len-n')) ts
| otherwise = drop' (n - len') ts
where len' = fromIntegral len
n' = fromIntegral n
-- | /O(n)/ 'takeWhile', applied to a predicate @p@ and a 'Text',
-- returns the longest prefix (possibly empty) of elements that
-- satisfy @p@. Subject to fusion.
takeWhile :: (Char -> Bool) -> Text -> Text
takeWhile p t0 = takeWhile' t0
where takeWhile' Empty = Empty
takeWhile' (Chunk t ts) =
case T.findIndex (not . p) t of
Just n | n > 0 -> Chunk (T.take n t) Empty
| otherwise -> Empty
Nothing -> Chunk t (takeWhile' ts)
{-# INLINE [1] takeWhile #-}
{-# RULES
"LAZY TEXT takeWhile -> fused" [~1] forall p t.
takeWhile p t = unstream (S.takeWhile p (stream t))
"LAZY TEXT takeWhile -> unfused" [1] forall p t.
unstream (S.takeWhile p (stream t)) = takeWhile p t
#-}
-- | /O(n)/ 'dropWhile' @p@ @t@ returns the suffix remaining after
-- 'takeWhile' @p@ @t@. Subject to fusion.
dropWhile :: (Char -> Bool) -> Text -> Text
dropWhile p t0 = dropWhile' t0
where dropWhile' Empty = Empty
dropWhile' (Chunk t ts) =
case T.findIndex (not . p) t of
Just n -> Chunk (T.drop n t) ts
Nothing -> dropWhile' ts
{-# INLINE [1] dropWhile #-}
{-# RULES
"LAZY TEXT dropWhile -> fused" [~1] forall p t.
dropWhile p t = unstream (S.dropWhile p (stream t))
"LAZY TEXT dropWhile -> unfused" [1] forall p t.
unstream (S.dropWhile p (stream t)) = dropWhile p t
#-}
-- | /O(n)/ 'dropWhileEnd' @p@ @t@ returns the prefix remaining after
-- dropping characters that fail the predicate @p@ from the end of
-- @t@.
-- Examples:
--
-- > dropWhileEnd (=='.') "foo..." == "foo"
dropWhileEnd :: (Char -> Bool) -> Text -> Text
dropWhileEnd p = go
where go Empty = Empty
go (Chunk t Empty) = if T.null t'
then Empty
else Chunk t' Empty
where t' = T.dropWhileEnd p t
go (Chunk t ts) = case go ts of
Empty -> go (Chunk t Empty)
ts' -> Chunk t ts'
{-# INLINE dropWhileEnd #-}
-- | /O(n)/ 'dropAround' @p@ @t@ returns the substring remaining after
-- dropping characters that fail the predicate @p@ from both the
-- beginning and end of @t@. Subject to fusion.
dropAround :: (Char -> Bool) -> Text -> Text
dropAround p = dropWhile p . dropWhileEnd p
{-# INLINE [1] dropAround #-}
-- | /O(n)/ Remove leading white space from a string. Equivalent to:
--
-- > dropWhile isSpace
stripStart :: Text -> Text
stripStart = dropWhile isSpace
{-# INLINE [1] stripStart #-}
-- | /O(n)/ Remove trailing white space from a string. Equivalent to:
--
-- > dropWhileEnd isSpace
stripEnd :: Text -> Text
stripEnd = dropWhileEnd isSpace
{-# INLINE [1] stripEnd #-}
-- | /O(n)/ Remove leading and trailing white space from a string.
-- Equivalent to:
--
-- > dropAround isSpace
strip :: Text -> Text
strip = dropAround isSpace
{-# INLINE [1] strip #-}
-- | /O(n)/ 'splitAt' @n t@ returns a pair whose first element is a
-- prefix of @t@ of length @n@, and whose second is the remainder of
-- the string. It is equivalent to @('take' n t, 'drop' n t)@.
splitAt :: Int64 -> Text -> (Text, Text)
splitAt = loop
where loop _ Empty = (empty, empty)
loop n t | n <= 0 = (empty, t)
loop n (Chunk t ts)
| n < len = let (t',t'') = T.splitAt (fromIntegral n) t
in (Chunk t' Empty, Chunk t'' ts)
| otherwise = let (ts',ts'') = loop (n - len) ts
in (Chunk t ts', ts'')
where len = fromIntegral (T.length t)
-- | /O(n)/ 'splitAtWord' @n t@ returns a strict pair whose first
-- element is a prefix of @t@ whose chunks contain @n@ 'Word16'
-- values, and whose second is the remainder of the string.
splitAtWord :: Int64 -> Text -> PairS Text Text
splitAtWord _ Empty = empty :*: empty
splitAtWord x (Chunk c@(T.Text arr off len) cs)
| y >= len = let h :*: t = splitAtWord (x-fromIntegral len) cs
in Chunk c h :*: t
| otherwise = chunk (textP arr off y) empty :*:
chunk (textP arr (off+y) (len-y)) cs
where y = fromIntegral x
-- | /O(n+m)/ Find the first instance of @needle@ (which must be
-- non-'null') in @haystack@. The first element of the returned tuple
-- is the prefix of @haystack@ before @needle@ is matched. The second
-- is the remainder of @haystack@, starting with the match.
--
-- Examples:
--
-- > breakOn "::" "a::b::c" ==> ("a", "::b::c")
-- > breakOn "/" "foobar" ==> ("foobar", "")
--
-- Laws:
--
-- > append prefix match == haystack
-- > where (prefix, match) = breakOn needle haystack
--
-- If you need to break a string by a substring repeatedly (e.g. you
-- want to break on every instance of a substring), use 'breakOnAll'
-- instead, as it has lower startup overhead.
--
-- This function is strict in its first argument, and lazy in its
-- second.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
breakOn :: Text -> Text -> (Text, Text)
breakOn pat src
| null pat = emptyError "breakOn"
| otherwise = case indices pat src of
[] -> (src, empty)
(x:_) -> let h :*: t = splitAtWord x src
in (h, t)
-- | /O(n+m)/ Similar to 'breakOn', but searches from the end of the string.
--
-- The first element of the returned tuple is the prefix of @haystack@
-- up to and including the last match of @needle@. The second is the
-- remainder of @haystack@, following the match.
--
-- > breakOnEnd "::" "a::b::c" ==> ("a::b::", "c")
breakOnEnd :: Text -> Text -> (Text, Text)
breakOnEnd pat src = let (a,b) = breakOn (reverse pat) (reverse src)
in (reverse b, reverse a)
{-# INLINE breakOnEnd #-}
-- | /O(n+m)/ Find all non-overlapping instances of @needle@ in
-- @haystack@. Each element of the returned list consists of a pair:
--
-- * The entire string prior to the /k/th match (i.e. the prefix)
--
-- * The /k/th match, followed by the remainder of the string
--
-- Examples:
--
-- > breakOnAll "::" ""
-- > ==> []
-- > breakOnAll "/" "a/b/c/"
-- > ==> [("a", "/b/c/"), ("a/b", "/c/"), ("a/b/c", "/")]
--
-- This function is strict in its first argument, and lazy in its
-- second.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
--
-- The @needle@ parameter may not be empty.
breakOnAll :: Text -- ^ @needle@ to search for
-> Text -- ^ @haystack@ in which to search
-> [(Text, Text)]
breakOnAll pat src
| null pat = emptyError "breakOnAll"
| otherwise = go 0 empty src (indices pat src)
where
go !n p s (x:xs) = let h :*: t = splitAtWord (x-n) s
h' = append p h
in (h',t) : go x h' t xs
go _ _ _ _ = []
-- | /O(n)/ 'break' is like 'span', but the prefix returned is over
-- elements that fail the predicate @p@.
break :: (Char -> Bool) -> Text -> (Text, Text)
break p t0 = break' t0
where break' Empty = (empty, empty)
break' c@(Chunk t ts) =
case T.findIndex p t of
Nothing -> let (ts', ts'') = break' ts
in (Chunk t ts', ts'')
Just n | n == 0 -> (Empty, c)
| otherwise -> let (a,b) = T.splitAt n t
in (Chunk a Empty, Chunk b ts)
-- | /O(n)/ 'span', applied to a predicate @p@ and text @t@, returns
-- a pair whose first element is the longest prefix (possibly empty)
-- of @t@ of elements that satisfy @p@, and whose second is the
-- remainder of the list.
span :: (Char -> Bool) -> Text -> (Text, Text)
span p = break (not . p)
{-# INLINE span #-}
-- | The 'group' function takes a 'Text' and returns a list of 'Text's
-- 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 :: Text -> [Text]
group = groupBy (==)
{-# INLINE group #-}
-- | The 'groupBy' function is the non-overloaded version of 'group'.
groupBy :: (Char -> Char -> Bool) -> Text -> [Text]
groupBy _ Empty = []
groupBy eq (Chunk t ts) = cons x ys : groupBy eq zs
where (ys,zs) = span (eq x) xs
x = T.unsafeHead t
xs = chunk (T.unsafeTail t) ts
-- | /O(n)/ Return all initial segments of the given 'Text',
-- shortest first.
inits :: Text -> [Text]
inits = (Empty :) . inits'
where inits' Empty = []
inits' (Chunk t ts) = L.map (\t' -> Chunk t' Empty) (L.tail (T.inits t))
++ L.map (Chunk t) (inits' ts)
-- | /O(n)/ Return all final segments of the given 'Text', longest
-- first.
tails :: Text -> [Text]
tails Empty = Empty : []
tails ts@(Chunk t ts')
| T.length t == 1 = ts : tails ts'
| otherwise = ts : tails (Chunk (T.unsafeTail t) ts')
-- $split
--
-- Splitting functions in this library do not perform character-wise
-- copies to create substrings; they just construct new 'Text's that
-- are slices of the original.
-- | /O(m+n)/ Break a 'Text' into pieces separated by the first
-- 'Text' argument, consuming the delimiter. An empty delimiter is
-- invalid, and will cause an error to be raised.
--
-- Examples:
--
-- > splitOn "\r\n" "a\r\nb\r\nd\r\ne" == ["a","b","d","e"]
-- > splitOn "aaa" "aaaXaaaXaaaXaaa" == ["","X","X","X",""]
-- > splitOn "x" "x" == ["",""]
--
-- and
--
-- > intercalate s . splitOn s == id
-- > splitOn (singleton c) == split (==c)
--
-- This function is strict in its first argument, and lazy in its
-- second.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
splitOn :: Text -- ^ Text to split on
-> Text -- ^ Input text
-> [Text]
splitOn pat src
| null pat = emptyError "splitOn"
| isSingleton pat = split (== head pat) src
| otherwise = go 0 (indices pat src) src
where
go _ [] cs = [cs]
go !i (x:xs) cs = let h :*: t = splitAtWord (x-i) cs
in h : go (x+l) xs (dropWords l t)
l = foldlChunks (\a (T.Text _ _ b) -> a + fromIntegral b) 0 pat
{-# INLINE [1] splitOn #-}
{-# RULES
"LAZY TEXT splitOn/singleton -> split/==" [~1] forall c t.
splitOn (singleton c) t = split (==c) t
#-}
-- | /O(n)/ Splits a 'Text' into components delimited by separators,
-- where the predicate returns True for a separator element. The
-- resulting components do not contain the separators. Two adjacent
-- separators result in an empty component in the output. eg.
--
-- > split (=='a') "aabbaca" == ["","","bb","c",""]
-- > split (=='a') [] == [""]
split :: (Char -> Bool) -> Text -> [Text]
split _ Empty = [Empty]
split p (Chunk t0 ts0) = comb [] (T.split p t0) ts0
where comb acc (s:[]) Empty = revChunks (s:acc) : []
comb acc (s:[]) (Chunk t ts) = comb (s:acc) (T.split p t) ts
comb acc (s:ss) ts = revChunks (s:acc) : comb [] ss ts
comb _ [] _ = impossibleError "split"
{-# INLINE split #-}
-- | /O(n)/ Splits a 'Text' into components of length @k@. The last
-- element may be shorter than the other chunks, depending on the
-- length of the input. Examples:
--
-- > chunksOf 3 "foobarbaz" == ["foo","bar","baz"]
-- > chunksOf 4 "haskell.org" == ["hask","ell.","org"]
chunksOf :: Int64 -> Text -> [Text]
chunksOf k = go
where
go t = case splitAt k t of
(a,b) | null a -> []
| otherwise -> a : go b
{-# INLINE chunksOf #-}
-- | /O(n)/ Breaks a 'Text' up into a list of 'Text's at
-- newline 'Char's. The resulting strings do not contain newlines.
lines :: Text -> [Text]
lines Empty = []
lines t = let (l,t') = break ((==) '\n') t
in l : if null t' then []
else lines (tail t')
-- | /O(n)/ Breaks a 'Text' up into a list of words, delimited by 'Char's
-- representing white space.
words :: Text -> [Text]
words = L.filter (not . null) . split isSpace
{-# INLINE words #-}
-- | /O(n)/ Joins lines, after appending a terminating newline to
-- each.
unlines :: [Text] -> Text
unlines = concat . L.map (`snoc` '\n')
{-# INLINE unlines #-}
-- | /O(n)/ Joins words using single space characters.
unwords :: [Text] -> Text
unwords = intercalate (singleton ' ')
{-# INLINE unwords #-}
-- | /O(n)/ The 'isPrefixOf' function takes two 'Text's and returns
-- 'True' iff the first is a prefix of the second. Subject to fusion.
isPrefixOf :: Text -> Text -> Bool
isPrefixOf Empty _ = True
isPrefixOf _ Empty = False
isPrefixOf (Chunk x xs) (Chunk y ys)
| lx == ly = x == y && isPrefixOf xs ys
| lx < ly = x == yh && isPrefixOf xs (Chunk yt ys)
| otherwise = xh == y && isPrefixOf (Chunk xt xs) ys
where (xh,xt) = T.splitAt ly x
(yh,yt) = T.splitAt lx y
lx = T.length x
ly = T.length y
{-# INLINE [1] isPrefixOf #-}
{-# RULES
"LAZY TEXT isPrefixOf -> fused" [~1] forall s t.
isPrefixOf s t = S.isPrefixOf (stream s) (stream t)
"LAZY TEXT isPrefixOf -> unfused" [1] forall s t.
S.isPrefixOf (stream s) (stream t) = isPrefixOf s t
#-}
-- | /O(n)/ The 'isSuffixOf' function takes two 'Text's and returns
-- 'True' iff the first is a suffix of the second.
isSuffixOf :: Text -> Text -> Bool
isSuffixOf x y = reverse x `isPrefixOf` reverse y
{-# INLINE isSuffixOf #-}
-- TODO: a better implementation
-- | /O(n+m)/ The 'isInfixOf' function takes two 'Text's and returns
-- 'True' iff the first is contained, wholly and intact, anywhere
-- within the second.
--
-- This function is strict in its first argument, and lazy in its
-- second.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
isInfixOf :: Text -> Text -> Bool
isInfixOf needle haystack
| null needle = True
| isSingleton needle = S.elem (head needle) . S.stream $ haystack
| otherwise = not . L.null . indices needle $ haystack
{-# INLINE [1] isInfixOf #-}
{-# RULES
"LAZY TEXT isInfixOf/singleton -> S.elem/S.stream" [~1] forall n h.
isInfixOf (singleton n) h = S.elem n (S.stream h)
#-}
-------------------------------------------------------------------------------
-- * View patterns
-- | /O(n)/ Return the suffix of the second string if its prefix
-- matches the entire first string.
--
-- Examples:
--
-- > stripPrefix "foo" "foobar" == Just "bar"
-- > stripPrefix "" "baz" == Just "baz"
-- > stripPrefix "foo" "quux" == Nothing
--
-- This is particularly useful with the @ViewPatterns@ extension to
-- GHC, as follows:
--
-- > {-# LANGUAGE ViewPatterns #-}
-- > import Data.Text.Lazy as T
-- >
-- > fnordLength :: Text -> Int
-- > fnordLength (stripPrefix "fnord" -> Just suf) = T.length suf
-- > fnordLength _ = -1
stripPrefix :: Text -> Text -> Maybe Text
stripPrefix p t
| null p = Just t
| otherwise = case commonPrefixes p t of
Just (_,c,r) | null c -> Just r
_ -> Nothing
-- | /O(n)/ Find the longest non-empty common prefix of two strings
-- and return it, along with the suffixes of each string at which they
-- no longer match.
--
-- If the strings do not have a common prefix or either one is empty,
-- this function returns 'Nothing'.
--
-- Examples:
--
-- > commonPrefixes "foobar" "fooquux" == Just ("foo","bar","quux")
-- > commonPrefixes "veeble" "fetzer" == Nothing
-- > commonPrefixes "" "baz" == Nothing
commonPrefixes :: Text -> Text -> Maybe (Text,Text,Text)
commonPrefixes Empty _ = Nothing
commonPrefixes _ Empty = Nothing
commonPrefixes a0 b0 = Just (go a0 b0 [])
where
go t0@(Chunk x xs) t1@(Chunk y ys) ps
= case T.commonPrefixes x y of
Just (p,a,b)
| T.null a -> go xs (chunk b ys) (p:ps)
| T.null b -> go (chunk a xs) ys (p:ps)
| otherwise -> (fromChunks (L.reverse (p:ps)),chunk a xs, chunk b ys)
Nothing -> (fromChunks (L.reverse ps),t0,t1)
go t0 t1 ps = (fromChunks (L.reverse ps),t0,t1)
-- | /O(n)/ Return the prefix of the second string if its suffix
-- matches the entire first string.
--
-- Examples:
--
-- > stripSuffix "bar" "foobar" == Just "foo"
-- > stripSuffix "" "baz" == Just "baz"
-- > stripSuffix "foo" "quux" == Nothing
--
-- This is particularly useful with the @ViewPatterns@ extension to
-- GHC, as follows:
--
-- > {-# LANGUAGE ViewPatterns #-}
-- > import Data.Text.Lazy as T
-- >
-- > quuxLength :: Text -> Int
-- > quuxLength (stripSuffix "quux" -> Just pre) = T.length pre
-- > quuxLength _ = -1
stripSuffix :: Text -> Text -> Maybe Text
stripSuffix p t = reverse `fmap` stripPrefix (reverse p) (reverse t)
-- | /O(n)/ 'filter', applied to a predicate and a 'Text',
-- returns a 'Text' containing those characters that satisfy the
-- predicate.
filter :: (Char -> Bool) -> Text -> Text
filter p t = unstream (S.filter p (stream t))
{-# INLINE filter #-}
-- | /O(n)/ The 'find' function takes a predicate and a 'Text', and
-- returns the first element in matching the predicate, or 'Nothing'
-- if there is no such element.
find :: (Char -> Bool) -> Text -> Maybe Char
find p t = S.findBy p (stream t)
{-# INLINE find #-}
-- | /O(n)/ The 'partition' function takes a predicate and a 'Text',
-- and returns the pair of 'Text's with elements which do and do not
-- satisfy the predicate, respectively; i.e.
--
-- > partition p t == (filter p t, filter (not . p) t)
partition :: (Char -> Bool) -> Text -> (Text, Text)
partition p t = (filter p t, filter (not . p) t)
{-# INLINE partition #-}
-- | /O(n)/ 'Text' index (subscript) operator, starting from 0.
index :: Text -> Int64 -> Char
index t n = S.index (stream t) n
{-# INLINE index #-}
-- | /O(n+m)/ The 'count' function returns the number of times the
-- query string appears in the given 'Text'. An empty query string is
-- invalid, and will cause an error to be raised.
--
-- In (unlikely) bad cases, this function's time complexity degrades
-- towards /O(n*m)/.
count :: Text -> Text -> Int64
count pat src
| null pat = emptyError "count"
| otherwise = go 0 (indices pat src)
where go !n [] = n
go !n (_:xs) = go (n+1) xs
{-# INLINE [1] count #-}
{-# RULES
"LAZY TEXT count/singleton -> countChar" [~1] forall c t.
count (singleton c) t = countChar c t
#-}
-- | /O(n)/ The 'countChar' function returns the number of times the
-- query element appears in the given 'Text'. Subject to fusion.
countChar :: Char -> Text -> Int64
countChar c t = S.countChar c (stream t)
-- | /O(n)/ 'zip' takes two 'Text's and returns a list of
-- corresponding pairs of bytes. If one input 'Text' is short,
-- excess elements of the longer 'Text' are discarded. This is
-- equivalent to a pair of 'unpack' operations.
zip :: Text -> Text -> [(Char,Char)]
zip a b = S.unstreamList $ S.zipWith (,) (stream a) (stream b)
{-# INLINE [0] zip #-}
-- | /O(n)/ 'zipWith' generalises 'zip' by zipping with the function
-- given as the first argument, instead of a tupling function.
-- Performs replacement on invalid scalar values.
zipWith :: (Char -> Char -> Char) -> Text -> Text -> Text
zipWith f t1 t2 = unstream (S.zipWith g (stream t1) (stream t2))
where g a b = safe (f a b)
{-# INLINE [0] zipWith #-}
revChunks :: [T.Text] -> Text
revChunks = L.foldl' (flip chunk) Empty
emptyError :: String -> a
emptyError fun = P.error ("Data.Text.Lazy." ++ fun ++ ": empty input")
impossibleError :: String -> a
impossibleError fun = P.error ("Data.Text.Lazy." ++ fun ++ ": impossible case")
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