RIO.Text

O(n) Convert a string to folded case.

This function is mainly useful for performing caseless (also known as 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 "ﬓ" (men now, U+FB13) is case folded to the sequence "մ" (men, U+0574) followed by "ն" (now, U+0576), while the Greek "µ" (micro sign, U+00B5) is case folded to "μ" (small letter mu, U+03BC) instead of itself.

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

The result string may be longer than the input string. For instance, "İ" (Latin capital letter I with dot above, U+0130) maps to the sequence "i" (Latin small letter i, U+0069) followed by " ̇" (combining dot above, U+0307).

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 "ß" (eszett, U+00DF) maps to the two-letter sequence "SS".

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.

This function is not idempotent. Consider lower-case letter ʼn (U+0149 LATIN SMALL LETTER N PRECEDED BY APOSTROPHE). Then T.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 T.toTitle "ʼN" = "'n".

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).

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.

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"

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"

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"

O(n) Concatenate a list of Texts.

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

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

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

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, ...]

Properties

head (scanl f z xs) = z

last (scanl f z xs) = foldl f z xs

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, ...]

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

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

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.

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.

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

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.

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.

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.

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

Examples:

>>> takeEnd 3 "foobar""bar"

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.

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

Examples:

>>> dropEnd 3 "foobar""foo"

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

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"

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

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"

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.

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

dropAround isSpace

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

dropWhile isSpace

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

dropWhileEnd isSpace

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).

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

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

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")

O(n) Group characters in a string by equality.

O(n) Group characters in a string according to a predicate.

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

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

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') ""[""]

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"]

O(n) Breaks a Text up into a list of Texts 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.

linesCR breaks a Text up into a list of Texts at newline Chars. It is very similar to lines, but it also removes any trailing 'r' characters. The resulting Text values do not contain newlines or trailing 'r' characters.

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

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

O(n) Joins words using single space characters.

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 as T

fnordLength :: Text -> Int
fnordLength (stripPrefix "fnord" -> Just suf) = T.length suf
fnordLength _                                 = -1

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 as T

quuxLength :: Text -> Int
quuxLength (stripSuffix "quux" -> Just pre) = T.length pre
quuxLength _                                = -1

Drop prefix if present, otherwise return original Text.

Drop prefix if present, otherwise return original Text.

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