text-2.0.2: An efficient packed Unicode text type.

Copyright | (c) 2009 2010 2012 Bryan O'Sullivan
License | BSD-style
Maintainer | bos@serpentine.com
Portability | GHC
Safe Haskell | Trustworthy
Language | Haskell2010

Data.Text.Lazy

Contents

- Fusion
- Acceptable data
- Types
- Creation and elimination
- Basic interface
- Transformations
  - Case conversion
  - Justification
- Folds
  - Special folds
- Construction
  - Scans
  - Accumulating maps
  - Generation and unfolding
- Substrings
  - Breaking strings
  - Breaking into many substrings
  - Breaking into lines and words
- Predicates
  - View patterns
- Searching
- Indexing
- Zipping and unzipping
- Orphan instances

Description

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

Synopsis

- data Text
- pack :: String -> Text
- unpack :: Text -> String
- singleton :: Char -> Text
- empty :: Text
- fromChunks :: [Text] -> Text
- toChunks :: Text -> [Text]
- toStrict :: Text -> Text
- fromStrict :: Text -> Text
- foldrChunks :: (Text -> a -> a) -> a -> Text -> a
- foldlChunks :: (a -> Text -> a) -> a -> Text -> a
- cons :: Char -> Text -> Text
- snoc :: Text -> Char -> Text
- append :: Text -> Text -> Text
- uncons :: Text -> Maybe (Char, Text)
- unsnoc :: Text -> Maybe (Text, Char)
- head :: HasCallStack => Text -> Char
- last :: HasCallStack => Text -> Char
- tail :: HasCallStack => Text -> Text
- init :: HasCallStack => Text -> Text
- null :: Text -> Bool
- length :: Text -> Int64
- compareLength :: Text -> Int64 -> Ordering
- map :: (Char -> Char) -> Text -> Text
- intercalate :: Text -> [Text] -> Text
- intersperse :: Char -> Text -> Text
- transpose :: [Text] -> [Text]
- reverse :: Text -> Text
- replace :: HasCallStack => Text -> Text -> Text -> Text
- toCaseFold :: Text -> Text
- toLower :: Text -> Text
- toUpper :: Text -> Text
- toTitle :: Text -> Text
- justifyLeft :: Int64 -> Char -> Text -> Text
- justifyRight :: Int64 -> Char -> Text -> Text
- center :: Int64 -> Char -> Text -> Text
- foldl :: (a -> Char -> a) -> a -> Text -> a
- foldl' :: (a -> Char -> a) -> a -> Text -> a
- foldl1 :: HasCallStack => (Char -> Char -> Char) -> Text -> Char
- foldl1' :: HasCallStack => (Char -> Char -> Char) -> Text -> Char
- foldr :: (Char -> a -> a) -> a -> Text -> a
- foldr1 :: HasCallStack => (Char -> Char -> Char) -> Text -> Char
- concat :: [Text] -> Text
- concatMap :: (Char -> Text) -> Text -> Text
- any :: (Char -> Bool) -> Text -> Bool
- all :: (Char -> Bool) -> Text -> Bool
- maximum :: HasCallStack => Text -> Char
- minimum :: HasCallStack => Text -> Char
- isAscii :: Text -> Bool
- 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)
- repeat :: Char -> Text
- replicate :: Int64 -> Text -> Text
- cycle :: HasCallStack => Text -> Text
- iterate :: (Char -> Char) -> Char -> Text
- unfoldr :: (a -> Maybe (Char, a)) -> a -> Text
- unfoldrN :: Int64 -> (a -> Maybe (Char, a)) -> a -> Text
- take :: Int64 -> Text -> Text
- takeEnd :: Int64 -> Text -> Text
- drop :: Int64 -> Text -> Text
- dropEnd :: Int64 -> Text -> Text
- takeWhile :: (Char -> Bool) -> Text -> Text
- takeWhileEnd :: (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)
- span :: (Char -> Bool) -> Text -> (Text, Text)
- spanM :: Monad m => (Char -> m Bool) -> Text -> m (Text, Text)
- spanEndM :: Monad m => (Char -> m Bool) -> Text -> m (Text, Text)
- breakOn :: HasCallStack => Text -> Text -> (Text, Text)
- breakOnEnd :: HasCallStack => Text -> Text -> (Text, Text)
- break :: (Char -> Bool) -> Text -> (Text, Text)
- group :: Text -> [Text]
- groupBy :: (Char -> Char -> Bool) -> Text -> [Text]
- inits :: Text -> [Text]
- tails :: Text -> [Text]
- splitOn :: HasCallStack => Text -> Text -> [Text]
- split :: (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
- stripPrefix :: Text -> Text -> Maybe Text
- stripSuffix :: Text -> Text -> Maybe Text
- commonPrefixes :: Text -> Text -> Maybe (Text, Text, Text)
- filter :: (Char -> Bool) -> Text -> Text
- find :: (Char -> Bool) -> Text -> Maybe Char
- elem :: Char -> Text -> Bool
- breakOnAll :: HasCallStack => Text -> Text -> [(Text, Text)]
- partition :: (Char -> Bool) -> Text -> (Text, Text)
- index :: HasCallStack => Text -> Int64 -> Char
- count :: HasCallStack => Text -> Text -> Int64
- zip :: Text -> Text -> [(Char, Char)]
- zipWith :: (Char -> Char -> Char) -> Text -> Text -> Text

# Fusion

Starting from `text-1.3` fusion is no longer implicit, and pipelines of transformations usually allocate intermediate `Text` values. Users, who observe significant changes to performances, are encouraged to use fusion framework explicitly, employing Data.Text.Internal.Fusion and Data.Text.Internal.Fusion.Common.

# Acceptable data

A `Text` value is a sequence of Unicode scalar values, as defined in §3.9, definition D76 of the Unicode 5.2 standard. As such, a `Text` cannot contain values in the range U+D800 to U+DFFF inclusive. Haskell implementations admit all Unicode code points (§3.4, definition D10) as `Char` values, including code points from this invalid range. This means that there are some `Char` values (corresponding to `Surrogate` category) 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 "�" (U+FFFD). Functions that perform this inspection and replacement are documented with the phrase "Performs replacement on invalid scalar values". The functions replace invalid scalar values, instead of dropping them, as a security measure. For details, see Unicode Technical Report 36, §3.5.)

# Types

data Text Source #

#### Instances

Instances details

Data Text Source # | This instance preserves data abstraction at the cost of inefficiency. We omit reflection services for the sake of data abstraction. This instance was created by copying the updated behavior of `Data.Text.``Text`

Instance details

Defined in Data.Text.Lazy

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Text -> c Text Source #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Text Source #

toConstr :: Text -> Constr Source #

dataTypeOf :: Text -> DataType Source #

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Text) Source #

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Text) Source #

gmapT :: (forall b. Data b => b -> b) -> Text -> Text Source #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Text -> r Source #

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Text -> r Source #

gmapQ :: (forall d. Data d => d -> u) -> Text -> [u] Source #

gmapQi :: Int -> (forall d. Data d => d -> u) -> Text -> u Source #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

IsString Text Source #

Performs replacement on invalid scalar values:

    >>> :set -XOverloadedStrings
    >>> "\55555" :: Data.Text.Lazy.Text
    "\65533"

Instance details Defined in Data.Text.Lazy Methods fromString :: String -> Text Source #
Monoid Text Source # |
Instance details Defined in Data.Text.Lazy Methods mempty :: Text Source # mappend :: Text -> Text -> Text Source # mconcat :: [Text] -> Text Source #
Semigroup Text Source # | Since: text-1.2.2.0
Instance details Defined in Data.Text.Lazy Methods (<>) :: Text -> Text -> Text Source # sconcat :: NonEmpty Text -> Text Source # stimes :: Integral b => b -> Text -> Text Source #

IsList Text Source #

Performs replacement on invalid scalar values:

    >>> :set -XOverloadedLists
    >>> ['\55555'] :: Data.Text.Lazy.Text
    "\65533"

Since: text-1.2.0.0

Instance details Defined in Data.Text.Lazy Associated Types type Item Text Source # Methods fromList :: [Item Text] -> Text Source # fromListN :: Int -> [Item Text] -> Text Source # toList :: Text -> [Item Text] Source #
Read Text Source # |
Instance details Defined in Data.Text.Lazy Methods readsPrec :: Int -> ReadS Text Source # readList :: ReadS [Text] Source # readPrec :: ReadPrec Text Source # readListPrec :: ReadPrec [Text] Source #
Show Text Source # |
Instance details Defined in Data.Text.Lazy Methods showsPrec :: Int -> Text -> ShowS Source # show :: Text -> String Source # showList :: [Text] -> ShowS Source #
PrintfArg Text Source # | Since: text-1.2.2.0
Instance details Defined in Data.Text.Lazy Methods formatArg :: Text -> FieldFormatter Source # parseFormat :: Text -> ModifierParser Source #
Binary Text Source # | Since: text-1.2.1.0
Instance details Defined in Data.Text.Lazy Methods put :: Text -> Put Source # get :: Get Text Source # putList :: [Text] -> Put Source #
NFData Text Source # |
Instance details Defined in Data.Text.Lazy Methods rnf :: Text -> () Source #
Eq Text Source # |
Instance details Defined in Data.Text.Lazy Methods (==) :: Text -> Text -> Bool Source # (/=) :: Text -> Text -> Bool Source #
Ord Text Source # |
Instance details Defined in Data.Text.Lazy Methods compare :: Text -> Text -> Ordering Source # (<) :: Text -> Text -> Bool Source # (<=) :: Text -> Text -> Bool Source # (>) :: Text -> Text -> Bool Source # (>=) :: Text -> Text -> Bool Source # max :: Text -> Text -> Text Source # min :: Text -> Text -> Text Source #
Lift Text Source # | Since: text-1.2.4.0
Instance details Defined in Data.Text.Lazy Methods lift :: Quote m => Text -> m Exp Source # liftTyped :: forall (m :: Type -> Type). Quote m => Text -> Code m Text Source #
type Item Text Source # |
Instance details Defined in Data.Text.Lazy type Item Text = Char

# Creation and elimination

pack :: String -> Text Source #

O(n) Convert a `String` into a `Text`.

Performs replacement on invalid scalar values, so ``unpack` . `pack`` is not `id`:

    >>> Data.Text.Lazy.unpack (Data.Text.Lazy.pack "\55555")
    "\65533"

unpack :: Text -> String Source #

O(n) Convert a `Text` into a `String`.

singleton :: Char -> Text Source #

O(1) Convert a character into a Text. Performs replacement on invalid scalar values.

empty :: Text Source #

Smart constructor for `Empty`.

fromChunks :: [Text] -> Text Source #

O(c) Convert a list of strict `Text`s into a lazy `Text`.

toChunks :: Text -> [Text] Source #

O(n) Convert a lazy `Text` into a list of strict `Text`s.

toStrict :: Text -> Text Source #

O(n) Convert a lazy `Text` into a strict `Text`.

fromStrict :: Text -> Text Source #

O(c) Convert a strict `Text` into a lazy `Text`.

foldrChunks :: (Text -> a -> a) -> a -> Text -> a Source #

Consume the chunks of a lazy `Text` with a natural right fold.

foldlChunks :: (a -> Text -> a) -> a -> Text -> a Source #

Consume the chunks of a lazy `Text` with a strict, tail-recursive, accumulating left fold.

# Basic interface

cons :: Char -> Text -> Text infixr 5 Source #

O(1) Adds a character to the front of a `Text`.

snoc :: Text -> Char -> Text Source #

O(n) Adds a character to the end of a `Text`. This copies the entire array in the process.

append :: Text -> Text -> Text Source #

O(n/c) Appends one `Text` to another.

uncons :: Text -> Maybe (Char, Text) Source #

O(1) Returns the first character and rest of a `Text`, or `Nothing` if empty.

unsnoc :: Text -> Maybe (Text, Char) Source #

O(n/c) Returns the `init` and `last` of a `Text`, or `Nothing` if empty.

- It is no faster than using `init` and `last`.

Since: text-1.2.3.0

head :: HasCallStack => Text -> Char Source #

O(1) Returns the first character of a `Text`, which must be non-empty. This is a partial function, consider using `uncons` instead.

last :: HasCallStack => Text -> Char Source #

O(n/c) Returns the last character of a `Text`, which must be non-empty. This is a partial function, consider using `unsnoc` instead.

tail :: HasCallStack => Text -> Text Source #

O(1) Returns all characters after the head of a `Text`, which must be non-empty. This is a partial function, consider using `uncons` instead.

init :: HasCallStack => Text -> Text Source #

O(n/c) Returns all but the last character of a `Text`, which must be non-empty. This is a partial function, consider using `unsnoc` instead.

null :: Text -> Bool Source #

O(1) Tests whether a `Text` is empty or not.

length :: Text -> Int64 Source #

O(n) Returns the number of characters in a `Text`.

compareLength :: Text -> Int64 -> Ordering Source #

O(min(n,c)) Compare the count of characters in a `Text` to a number.

    compareLength t c = compare (length t) c

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.

# Transformations

map :: (Char -> Char) -> Text -> Text Source #

O(n) `map` `f` `t` is the `Text` obtained by applying `f` to each element of `t`. Performs replacement on invalid scalar values.

intercalate :: Text -> [Text] -> Text Source #

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.

intersperse :: Char -> Text -> Text Source #

O(n) The `intersperse` function takes a character and places it between the characters of a `Text`. Performs replacement on invalid scalar values.

transpose :: [Text] -> [Text] Source #

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.

reverse :: Text -> Text Source #

O(n) `reverse` `t` returns the elements of `t` in reverse order.

replace Source #

Arguments

:: HasCallStack |
=> Text | `needle` to search for. If this string is empty, an error will occur.
-> Text | `replacement` to replace `needle` with.
-> Text | `haystack` in which to search.
-> Text |

O(m+n) Replace every non-overlapping occurrence of `needle` in `haystack` with `replacement`.

This function behaves as though it was defined as follows:

    replace needle replacement haystack =
      intercalate replacement (splitOn needle haystack)

As this suggests, each occurrence is replaced exactly once. So if `needle` occurs in `replacement`, that occurrence will not itself be replaced recursively:

    replace "oo" "foo" "oo" == "foo"

In cases where several instances of `needle` overlap, only the first one will be replaced:

    replace "ofo" "bar" "ofofo" == "barfo"

In (unlikely) bad cases, this function's time complexity degrades towards O(n*m).

## Case conversion

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.

toCaseFold :: Text -> Text Source #

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.

toLower :: Text -> Text Source #

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).

toUpper :: Text -> Text Source #

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.

toTitle :: Text -> Text Source #

O(n) Convert a string to title case, using simple case conversion.

The first letter (as determined by `isLetter`) of the input is converted to title case, as is every subsequent letter that immediately follows a non-letter. Every letter that immediately follows another letter is converted to lower case.

The result string may be longer than the input string. For example, the Latin small ligature ﬂ (U+FB02) is converted to the sequence Latin capital letter F (U+0046) followed by Latin small letter l (U+006C).

This function is not idempotent. Consider lower-case letter `ŉ` (U+0149 LATIN SMALL LETTER N PRECEDED BY APOSTROPHE). Then `toTitle` `"ŉ"` = `"ʼN"`: the first (and the only) letter of the input is converted to title case, becoming two letters. Now `ʼ` (U+02BC MODIFIER LETTER APOSTROPHE) is a modifier letter and as such is recognised as a letter by `isLetter`, so `toTitle` `"ʼN"` = `"'n"`.

Note: this function does not take language or culture specific rules into account. For instance, in English, different style guides disagree on whether the book name "The Hill of the Red Fox" is correctly title cased—but this function will capitalize every word.

Since: text-1.0.0.0

## Justification

justifyLeft :: Int64 -> Char -> Text -> Text Source #

O(n) Left-justify a string to the given length, using the specified fill character on the right. Performs replacement on invalid scalar values.

Examples:

    justifyLeft 7 'x' "foo"    == "fooxxxx"
    justifyLeft 3 'x' "foobar" == "foobar"

justifyRight :: Int64 -> Char -> Text -> Text Source #

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"

center :: Int64 -> Char -> Text -> Text Source #

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"

# Folds

foldl :: (a -> Char -> a) -> a -> Text -> a Source #

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.

foldl' :: (a -> Char -> a) -> a -> Text -> a Source #

O(n) A strict version of `foldl`.

foldl1 :: HasCallStack => (Char -> Char -> Char) -> Text -> Char Source #

O(n) A variant of `foldl` that has no starting value argument, and thus must be applied to a non-empty `Text`.

foldl1' :: HasCallStack => (Char -> Char -> Char) -> Text -> Char Source #

O(n) A strict version of `foldl1`.

foldr :: (Char -> a -> a) -> a -> Text -> a Source #

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.

`foldr` is lazy like `foldr` for lists: evaluation actually traverses the `Text` from left to right, only as far as it needs to.

For example, `head` can be defined with O(1) complexity using `foldr`:

    head :: Text -> Char
    head = foldr const (error "head empty")

foldr1 :: HasCallStack => (Char -> Char -> Char) -> Text -> Char Source #

O(n) A variant of `foldr` that has no starting value argument, and thus must be applied to a non-empty `Text`.

## Special folds

concat :: [Text] -> Text Source #

O(n) Concatenate a list of `Text`s.

concatMap :: (Char -> Text) -> Text -> Text Source #

O(n) Map a function over a `Text` that results in a `Text`, and concatenate the results.

any :: (Char -> Bool) -> Text -> Bool Source #

O(n) `any` `p` `t` determines whether any character in the `Text` `t` satisfies the predicate `p`.

all :: (Char -> Bool) -> Text -> Bool Source #

O(n) `all` `p` `t` determines whether all characters in the `Text` `t` satisfy the predicate `p`.

maximum :: HasCallStack => Text -> Char Source #

O(n) `maximum` returns the maximum value from a `Text`, which must be non-empty.

minimum :: HasCallStack => Text -> Char Source #

O(n) `minimum` returns the minimum value from a `Text`, which must be non-empty.

isAscii :: Text -> Bool Source #

O(n) Test whether `Text` contains only ASCII code-points (i.e. only U+0000 through U+007F).

This is a more efficient version of ``all` `isAscii``.

    >>> isAscii ""
    True

    >>> isAscii "abc\NUL"
    True

    >>> isAscii "abcd€"
    False

    isAscii t == all (< '\x80') t

Since: text-2.0.2

# Construction

## Scans

scanl :: (Char -> Char -> Char) -> Char -> Text -> Text Source #

O(n) `scanl` is similar to `foldl`, but returns a list of successive reduced values from the left. 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.

scanl1 :: (Char -> Char -> Char) -> Text -> Text Source #

O(n) `scanl1` is a variant of `scanl` that has no starting value argument. Performs replacement on invalid scalar values.

    scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]

scanr :: (Char -> Char -> Char) -> Char -> Text -> Text Source #

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

scanr1 :: (Char -> Char -> Char) -> Text -> Text Source #

O(n) `scanr1` is a variant of `scanr` that has no starting value argument. Performs replacement on invalid scalar values.

## Accumulating maps

mapAccumL :: (a -> Char -> (a, Char)) -> a -> Text -> (a, Text) Source #

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.

mapAccumR :: (a -> Char -> (a, Char)) -> a -> Text -> (a, Text) Source #

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.

## Generation and unfolding

repeat :: Char -> Text Source #

``repeat` x` is an infinite `Text`, with `x` the value of every element.

Since: text-1.2.0.5

replicate :: Int64 -> Text -> Text Source #

O(n*m) `replicate` `n` `t` is a `Text` consisting of the input `t` repeated `n` times.

cycle :: HasCallStack => Text -> Text Source #

`cycle` ties a finite, non-empty `Text` into a circular one, or equivalently, the infinite repetition of the original `Text`.

Since: text-1.2.0.5

iterate :: (Char -> Char) -> Char -> Text Source #

``iterate` f x` returns an infinite `Text` of repeated applications of `f` to `x`:

    iterate f x == [x, f x, f (f x), ...]

Since: text-1.2.0.5

unfoldr :: (a -> Maybe (Char, a)) -> a -> Text Source #

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. Performs replacement on invalid scalar values.

unfoldrN :: Int64 -> (a -> Maybe (Char, a)) -> a -> Text Source #

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.

# Substrings

## Breaking strings

take :: Int64 -> Text -> Text Source #

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.

takeEnd :: Int64 -> Text -> Text Source #

O(n) `takeEnd` `n` `t` returns the suffix remaining after taking `n` characters from the end of `t`.

Examples:

    takeEnd 3 "foobar" == "bar"

Since: text-1.1.1.0

drop :: Int64 -> Text -> Text Source #

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`.

dropEnd :: Int64 -> Text -> Text Source #

O(n) `dropEnd` `n` `t` returns the prefix remaining after dropping `n` characters from the end of `t`.

Examples:

    dropEnd 3 "foobar" == "foo"

Since: text-1.1.1.0

takeWhile :: (Char -> Bool) -> Text -> Text Source #

O(n) `takeWhile`, applied to a predicate `p` and a `Text`, returns the longest prefix (possibly empty) of elements that satisfy `p`.

takeWhileEnd :: (Char -> Bool) -> Text -> Text Source #

O(n) `takeWhileEnd`, applied to a predicate `p` and a `Text`, returns the longest suffix (possibly empty) of elements that satisfy `p`. Examples:

    takeWhileEnd (=='o') "foo" == "oo"

Since: text-1.2.2.0

dropWhile :: (Char -> Bool) -> Text -> Text Source #

O(n) `dropWhile` `p` `t` returns the suffix remaining after `takeWhile` `p` `t`.

dropWhileEnd :: (Char -> Bool) -> Text -> Text Source #

O(n) `dropWhileEnd` `p` `t` returns the prefix remaining after dropping characters that satisfy the predicate `p` from the end of `t`.

Examples:

    dropWhileEnd (=='.') "foo..." == "foo"

dropAround :: (Char -> Bool) -> Text -> Text Source #

O(n) `dropAround` `p` `t` returns the substring remaining after dropping characters that satisfy the predicate `p` from both the beginning and end of `t`.

strip :: Text -> Text Source #

O(n) Remove leading and trailing white space from a string. Equivalent to:

    dropAround isSpace

stripStart :: Text -> Text Source #

O(n) Remove leading white space from a string. Equivalent to:

    dropWhile isSpace

stripEnd :: Text -> Text Source #

O(n) Remove trailing white space from a string. Equivalent to:

    dropWhileEnd isSpace

splitAt :: Int64 -> Text -> (Text, Text) Source #

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)`.

span :: (Char -> Bool) -> Text -> (Text, Text) Source #

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 text.

    >>> T.span (=='0') "000AB"
    ("000","AB")

spanM :: Monad m => (Char -> m Bool) -> Text -> m (Text, Text) Source #

O(length of prefix) `spanM`, applied to a monadic predicate `p`, a text `t`, returns a pair `(t1, t2)` where `t1` is the longest prefix of `t` whose elements satisfy `p`, and `t2` is the remainder of the text.

    >>> T.spanM (\c -> state $ \i -> (fromEnum c == i, i+1)) "abcefg" `runState` 97
    (("abc","efg"),101)

`span` is `spanM` specialized to `Identity`:

    -- for all p :: Char -> Bool
    span p = runIdentity . spanM (pure . p)

Since: text-2.0.1

spanEndM :: Monad m => (Char -> m Bool) -> Text -> m (Text, Text) Source #

O(length of suffix) `spanEndM`, applied to a monadic predicate `p`, a text `t`, returns a pair `(t1, t2)` where `t2` is the longest suffix of `t` whose elements satisfy `p`, and `t1` is the remainder of the text.

    >>> T.spanEndM (\c -> state $ \i -> (fromEnum c == i, i-1)) "tuvxyz" `runState` 122
    (("tuv","xyz"),118)

    spanEndM p . reverse = fmap (bimap reverse reverse) . spanM p

Since: text-2.0.1

breakOn :: HasCallStack => Text -> Text -> (Text, Text) Source #

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).

breakOnEnd :: HasCallStack => Text -> Text -> (Text, Text) Source #

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")

break :: (Char -> Bool) -> Text -> (Text, Text) Source #

O(n) `break` is like `span`, but the prefix returned is over elements that fail the predicate `p`.

    >>> T.break (=='c') "180cm"
    ("180","cm")

group :: Text -> [Text] Source #

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.

groupBy :: (Char -> Char -> Bool) -> Text -> [Text] Source #

The `groupBy` function is the non-overloaded version of `group`.

inits :: Text -> [Text] Source #

O(n) Return all initial segments of the given `Text`, shortest first.

tails :: Text -> [Text] Source #

O(n) Return all final segments of the given `Text`, longest first.

## Breaking into many substrings

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.

splitOn Source #

Arguments

:: HasCallStack |
=> Text | String to split on. If this string is empty, an error will occur.
-> Text | Input text.
-> [Text] |

O(m+n) Break a `Text` into pieces separated by the first `Text` argument (which cannot be an empty string), 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)

(Note: the string `s` to split on above cannot be empty.)

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).

split :: (Char -> Bool) -> Text -> [Text] Source #

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') []        == [""]

chunksOf :: Int64 -> Text -> [Text] Source #

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"]

## Breaking into lines and words

lines :: Text -> [Text] Source #

O(n) Breaks a `Text` up into a list of `Text`s at newline characters `'\n'` (LF, line feed). The resulting strings do not contain newlines.

`lines` does not treat `'\r'` (CR, carriage return) as a newline character.

words :: Text -> [Text] Source #

O(n) Breaks a `Text` up into a list of words, delimited by `Char`s representing white space.

unlines :: [Text] -> Text Source #

O(n) Joins lines, after appending a terminating newline to each.

unwords :: [Text] -> Text Source #

O(n) Joins words using single space characters.

# Predicates

isPrefixOf :: Text -> Text -> Bool Source #

O(n) The `isPrefixOf` function takes two `Text`s and returns `True` if and only if the first is a prefix of the second.

isSuffixOf :: Text -> Text -> Bool Source #

O(n) The `isSuffixOf` function takes two `Text`s and returns `True` if and only if the first is a suffix of the second.

isInfixOf :: Text -> Text -> Bool Source #

O(n+m) The `isInfixOf` function takes two `Text`s and returns `True` if and only if 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).

## View patterns

stripPrefix :: Text -> Text -> Maybe Text Source #

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

stripSuffix :: Text -> Text -> Maybe Text Source #

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

commonPrefixes :: Text -> Text -> Maybe (Text, Text, Text) Source #

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

# Searching

filter :: (Char -> Bool) -> Text -> Text Source #

O(n) `filter`, applied to a predicate and a `Text`, returns a `Text` containing those characters that satisfy the predicate.

find :: (Char -> Bool) -> Text -> Maybe Char Source #

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.

elem :: Char -> Text -> Bool Source #

O(n) The `elem` function takes a character and a `Text`, and returns `True` if the element is found in the given `Text`, or `False` otherwise.

breakOnAll Source #

Arguments

:: HasCallStack |
=> Text | `needle` to search for
-> Text | `haystack` in which to search
-> [(Text, Text)] |

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 kth match (i.e. the prefix)
- The kth 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.

partition :: (Char -> Bool) -> Text -> (Text, Text) Source #

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)

# Indexing

index :: HasCallStack => Text -> Int64 -> Char Source #

O(n) `Text` index (subscript) operator, starting from 0.

count :: HasCallStack => Text -> Text -> Int64 Source #

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).

# Zipping and unzipping

zip :: Text -> Text -> [(Char, Char)] Source #

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.

zipWith :: (Char -> Char -> Char) -> Text -> Text -> Text Source #

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.

# Orphan instances

Data Text Source # | This instance preserves data abstraction at the cost of inefficiency. We omit reflection services for the sake of data abstraction. This instance was created by copying the updated behavior of `Data.Text.``Text`

Instance details

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Text -> c Text Source #

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Text Source #

toConstr :: Text -> Constr Source #

dataTypeOf :: Text -> DataType Source #

dataCast1 :: Typeable t => (forall d. Data d => c (t d)) -> Maybe (c Text) Source #

dataCast2 :: Typeable t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Text) Source #

gmapT :: (forall b. Data b => b -> b) -> Text -> Text Source #

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Text -> r Source #

gmapQr :: forall r r'. (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Text -> r Source #

gmapQ :: (forall d. Data d => d -> u) -> Text -> [u] Source #

gmapQi :: Int -> (forall d. Data d => d -> u) -> Text -> u Source #

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Text -> m Text Source #

IsString Text Source #

Performs replacement on invalid scalar values:

    >>> :set -XOverloadedStrings
    >>> "\55555" :: Data.Text.Lazy.Text
    "\65533"

Instance details Methods fromString :: String -> Text Source #
Monoid Text Source # |
Instance details Methods mempty :: Text Source # mappend :: Text -> Text -> Text Source # mconcat :: [Text] -> Text Source #
Semigroup Text Source # | Since: text-1.2.2.0
Instance details Methods (<>) :: Text -> Text -> Text Source # sconcat :: NonEmpty Text -> Text Source # stimes :: Integral b => b -> Text -> Text Source #

IsList Text Source #

Performs replacement on invalid scalar values:

    >>> :set -XOverloadedLists
    >>> ['\55555'] :: Data.Text.Lazy.Text
    "\65533"

Since: text-1.2.0.0

Instance details Associated Types type Item Text Source # Methods fromList :: [Item Text] -> Text Source # fromListN :: Int -> [Item Text] -> Text Source # toList :: Text -> [Item Text] Source #
Read Text Source # |
Instance details Methods readsPrec :: Int -> ReadS Text Source # readList :: ReadS [Text] Source # readPrec :: ReadPrec Text Source # readListPrec :: ReadPrec [Text] Source #
Show Text Source # |
Instance details Methods showsPrec :: Int -> Text -> ShowS Source # show :: Text -> String Source # showList :: [Text] -> ShowS Source #
PrintfArg Text Source # | Since: text-1.2.2.0
Instance details Methods formatArg :: Text -> FieldFormatter Source # parseFormat :: Text -> ModifierParser Source #
Binary Text Source # | Since: text-1.2.1.0
Instance details Methods put :: Text -> Put Source # get :: Get Text Source # putList :: [Text] -> Put Source #
NFData Text Source # |
Instance details Methods rnf :: Text -> () Source #
Eq Text Source # |
Instance details Methods (==) :: Text -> Text -> Bool Source # (/=) :: Text -> Text -> Bool Source #
Ord Text Source # |
Instance details Methods compare :: Text -> Text -> Ordering Source # (<) :: Text -> Text -> Bool Source # (<=) :: Text -> Text -> Bool Source # (>) :: Text -> Text -> Bool Source # (>=) :: Text -> Text -> Bool Source # max :: Text -> Text -> Text Source # min :: Text -> Text -> Text Source #
Lift Text Source # | Since: text-1.2.4.0
Instance details Methods lift :: Quote m => Text -> m Exp Source # liftTyped :: forall (m :: Type -> Type). Quote m => Text -> Code m Text Source #