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Data.Text.Lazy | Portability | GHC | Stability | experimental | Maintainer | bos@serpentine.com, rtharper@aftereternity.co.uk,
duncan@haskell.org |
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Description |
A time and space-efficient implementation of Unicode text using
lists of packed arrays. This representation 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 complexity than their Data.Text equivalents, due to
optimisations resulting from the list spine structure. And for
other operations lazy Texts are usually within a few percent of
strict ones, but with better heap usage. 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 B
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Synopsis |
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data Text | | pack :: String -> Text | | unpack :: Text -> String | | singleton :: Char -> Text | | empty :: Text | | fromChunks :: [Text] -> Text | | toChunks :: Text -> [Text] | | cons :: Char -> Text -> Text | | snoc :: Text -> Char -> Text | | append :: Text -> Text -> Text | | uncons :: Text -> Maybe (Char, Text) | | head :: Text -> Char | | last :: Text -> Char | | tail :: Text -> Text | | init :: Text -> Text | | null :: Text -> Bool | | length :: Text -> Int64 | | map :: (Char -> Char) -> Text -> Text | | intercalate :: Text -> [Text] -> Text | | intersperse :: Char -> Text -> Text | | transpose :: [Text] -> [Text] | | reverse :: Text -> Text | | replace :: Text -> Text -> Text -> Text | | toCaseFold :: Text -> Text | | toLower :: Text -> Text | | toUpper :: Text -> Text | | justifyLeft :: Int64 -> Char -> Text -> Text | | justifyRight :: Int64 -> Char -> Text -> Text | | center :: Int64 -> Char -> Text -> Text | | foldl :: (b -> Char -> b) -> b -> Text -> b | | foldl' :: (b -> Char -> b) -> b -> Text -> b | | foldl1 :: (Char -> Char -> Char) -> Text -> Char | | foldl1' :: (Char -> Char -> Char) -> Text -> Char | | foldr :: (Char -> b -> b) -> b -> Text -> b | | foldr1 :: (Char -> Char -> Char) -> Text -> Char | | concat :: [Text] -> Text | | concatMap :: (Char -> Text) -> Text -> Text | | any :: (Char -> Bool) -> Text -> Bool | | all :: (Char -> Bool) -> Text -> Bool | | maximum :: Text -> Char | | minimum :: Text -> Char | | scanl :: (Char -> Char -> Char) -> Char -> Text -> Text | | scanl1 :: (Char -> Char -> Char) -> Text -> Text | | scanr :: (Char -> Char -> Char) -> Char -> Text -> Text | | scanr1 :: (Char -> Char -> Char) -> Text -> Text | | mapAccumL :: (a -> Char -> (a, Char)) -> a -> Text -> (a, Text) | | mapAccumR :: (a -> Char -> (a, Char)) -> a -> Text -> (a, Text) | | replicate :: Int64 -> Text -> Text | | unfoldr :: (a -> Maybe (Char, a)) -> a -> Text | | unfoldrN :: Int64 -> (a -> Maybe (Char, a)) -> a -> Text | | take :: Int64 -> Text -> Text | | drop :: Int64 -> Text -> Text | | takeWhile :: (Char -> Bool) -> Text -> Text | | dropWhile :: (Char -> Bool) -> Text -> Text | | dropWhileEnd :: (Char -> Bool) -> Text -> Text | | dropAround :: (Char -> Bool) -> Text -> Text | | strip :: Text -> Text | | stripStart :: Text -> Text | | stripEnd :: Text -> Text | | splitAt :: Int64 -> Text -> (Text, Text) | | spanBy :: (Char -> Bool) -> Text -> (Text, Text) | | break :: Text -> Text -> (Text, Text) | | breakEnd :: Text -> Text -> (Text, Text) | | breakBy :: (Char -> Bool) -> Text -> (Text, Text) | | group :: Text -> [Text] | | groupBy :: (Char -> Char -> Bool) -> Text -> [Text] | | inits :: Text -> [Text] | | tails :: Text -> [Text] | | split :: Text -> Text -> [Text] | | splitBy :: (Char -> Bool) -> Text -> [Text] | | chunksOf :: Int64 -> Text -> [Text] | | lines :: Text -> [Text] | | words :: Text -> [Text] | | unlines :: [Text] -> Text | | unwords :: [Text] -> Text | | isPrefixOf :: Text -> Text -> Bool | | isSuffixOf :: Text -> Text -> Bool | | isInfixOf :: Text -> Text -> Bool | | filter :: (Char -> Bool) -> Text -> Text | | find :: Text -> Text -> (Text, [(Text, Text)]) | | findBy :: (Char -> Bool) -> Text -> Maybe Char | | partitionBy :: (Char -> Bool) -> Text -> (Text, Text) | | index :: Text -> Int64 -> Char | | count :: Text -> Text -> Int64 | | zip :: Text -> Text -> [(Char, Char)] | | zipWith :: (Char -> Char -> Char) -> Text -> Text -> Text |
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Documentation |
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Creation and elimination
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O(n) Convert a String into a Text.
This function is subject to array fusion.
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O(n) Convert a Text into a String.
Subject to array fusion.
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Smart constructor for Empty.
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O(c) Convert a list of strict Texts into a lazy Text.
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O(n) Convert a lazy Text into a list of strict Texts.
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Basic interface
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O(n\c)/ Appends one Text to another. Subject to array
fusion.
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O(1) Returns the first character and rest of a Text, or
Nothing if empty. Subject to array fusion.
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O(1) Returns the first character of a Text, which must be
non-empty. Subject to array fusion.
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O(1) Returns the last character of a Text, which must be
non-empty. Subject to array fusion.
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O(1) Returns all characters after the head of a Text, which
must be non-empty. Subject to array fusion.
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O(1) Returns all but the last character of a Text, which must
be non-empty. Subject to array fusion.
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O(1) Tests whether a Text is empty or not. Subject to array
fusion.
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Transformations
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O(n) map f t is the Text obtained by applying f to
each element of t. Subject to array fusion.
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O(n) The intercalate function takes a Text and a list of
Texts and concatenates the list after interspersing the first
argument between each element of the list.
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O(n) The intersperse function takes a character and places it
between the characters of a Text. Subject to array fusion.
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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.
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O(n) reverse t returns the elements of t in reverse order.
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:: Text | Text to search for
| -> Text | Replacement text
| -> Text | Input text
| -> Text | | O(m+n) Replace every occurrence of one substring with another.
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Case conversion
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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.
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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.
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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).
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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.
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Justification
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O(n) Left-justify a string to the given length, using the
specified fill character on the right. Subject to fusion. Examples:
justifyLeft 7 'x' "foo" == "fooxxxx"
justifyLeft 3 'x' "foobar" == "foobar"
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O(n) Right-justify a string to the given length, using the
specified fill character on the left. Examples:
justifyRight 7 'x' "bar" == "xxxxbar"
justifyRight 3 'x' "foobar" == "foobar"
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O(n) Center a string to the given length, using the
specified fill character on either side. Examples:
center 8 'x' "HS" = "xxxHSxxx"
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Folds
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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 array fusion.
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O(n) A strict version of foldl.
Subject to array fusion.
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O(n) A variant of foldl that has no starting value argument,
and thus must be applied to a non-empty Text. Subject to array
fusion.
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O(n) A strict version of foldl1.
Subject to array fusion.
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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 array fusion.
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O(n) A variant of foldr that has no starting value argument, and
thust must be applied to a non-empty Text. Subject to array
fusion.
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Special folds
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O(n) Concatenate a list of Texts.
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O(n) Map a function over a Text that results in a Text, and
concatenate the results.
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O(n) any p t determines whether any character in the
Text t satisifes the predicate p. Subject to array fusion.
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O(n) all p t determines whether all characters in the
Text t satisify the predicate p. Subject to array fusion.
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O(n) maximum returns the maximum value from a Text, which
must be non-empty. Subject to array fusion.
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O(n) minimum returns the minimum value from a Text, which
must be non-empty. Subject to array fusion.
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Construction
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Scans
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O(n) scanl is similar to foldl, but returns a list of
successive reduced values from the left. This function is subject
to array fusion.
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.
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O(n) scanl1 is a variant of scanl that has no starting
value argument. This function is subject to array fusion.
scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
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O(n) scanr is the right-to-left dual of scanl.
scanr f v == reverse . scanl (flip f) v . reverse
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O(n) scanr1 is a variant of scanr that has no starting
value argument.
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Accumulating maps
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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.
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The mapAccumR function behaves like a combination of map and
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.
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Generation and unfolding
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O(n*m) replicate n t is a Text consisting of the input
t repeated n times.
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O(n), where n is the length of the result. The unfoldr
function is analogous to the List 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.
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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.
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Substrings
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Breaking strings
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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.
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O(n) drop n, applied to a Text, returns the suffix of the
Text of length n, or the empty Text if n is greater than the
length of the Text. Subject to fusion.
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O(n) takeWhile, applied to a predicate p and a Text, returns
the longest prefix (possibly empty) of elements that satisfy p.
This function is subject to array fusion.
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O(n) dropWhile p t returns the suffix remaining after
takeWhile p t. This function is subject to array fusion.
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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"
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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.
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O(n) Remove leading and trailing white space from a string.
Equivalent to:
dropAround isSpace
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O(n) Remove leading white space from a string. Equivalent to:
dropWhile isSpace
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O(n) Remove trailing white space from a string. Equivalent to:
dropWhileEnd isSpace
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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).
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O(n) spanBy, 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.
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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:
break "::" "a::b::c" ==> ("a", "::b::c")
break "/" "foobar" ==> ("foobar", "")
Laws:
append prefix match == haystack
where (prefix, match) = break 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 find
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).
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O(n+m) Similar to break, 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.
breakEnd "::" "a::b::c" ==> ("a::b::", "c")
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O(n) breakBy is like spanBy, but the prefix returned is over
elements that fail the predicate p.
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The group function takes a Text and returns a list of Texts
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.
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The groupBy function is the non-overloaded version of group.
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O(n) Return all initial segments of the given Text,
shortest first.
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O(n) Return all final segments of the given Text, longest
first.
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Breaking into many substrings
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Splitting functions in this library do not perform character-wise
copies to create substrings; they just construct new Texts that
are slices of the original.
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:: Text | Text to split on
| -> Text | Input text
| -> [Text] | | 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:
split "\r\n" "a\r\nb\r\nd\r\ne" == ["a","b","d","e"]
split "aaa" "aaaXaaaXaaaXaaa" == ["","X","X","X",""]
split "x" "x" == ["",""]
and
intercalate s . split s == id
split (singleton c) == splitBy (==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).
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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.
splitBy (=='a') "aabbaca" == ["","","bb","c",""]
splitBy (=='a') [] == [""]
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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"]
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Breaking into lines and words
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O(n) Breaks a Text up into a list of Texts at
newline Chars. The resulting strings do not contain newlines.
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O(n) Breaks a Text up into a list of words, delimited by Chars
representing white space.
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O(n) Joins lines, after appending a terminating newline to
each.
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O(n) Joins words using single space characters.
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Predicates
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O(n) The isPrefixOf function takes two Texts and returns
True iff the first is a prefix of the second. This function is
subject to fusion.
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O(n) The isSuffixOf function takes two Texts and returns
True iff the first is a suffix of the second.
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O(n+m) The isInfixOf function takes two Texts 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).
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Searching
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O(n) filter, applied to a predicate and a Text,
returns a Text containing those characters that satisfy the
predicate.
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O(n+m) Find all non-overlapping instances of needle in
haystack. The first element of the returned pair is the prefix
of haystack prior to any matches of needle. The second is a
list of pairs.
The first element of each pair in the list is a span from the
beginning of a match to the beginning of the next match, while the
second is a span from the beginning of the match to the end of the
input.
Examples:
find "::" ""
==> ("", [])
find "/" "a/b/c/d"
==> ("a", [("/b","/b/c/d"), ("/c","/c/d"), ("/d","/d")])
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).
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O(n) The findBy function takes a predicate and a Text, and
returns the first element in matching the predicate, or Nothing
if there is no such element.
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O(n) The partitionBy function takes a predicate and a Text,
and returns the pair of Texts with elements which do and do not
satisfy the predicate, respectively; i.e.
partitionBy p t == (filter p t, filter (not . p) t)
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Indexing
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O(n) Text index (subscript) operator, starting from 0.
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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).
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Zipping and unzipping
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O(n) zip takes two Texts 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.
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O(n) zipWith generalises zip by zipping with the function
given as the first argument, instead of a tupling function.
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Produced by Haddock version 2.6.1 |