data Char :: * Source

The character type Char is an enumeration whose values represent Unicode (or equivalently ISO/IEC 10646) characters (see http://www.unicode.org/ for details). This set extends the ISO 8859-1 (Latin-1) character set (the first 256 characters), which is itself an extension of the ASCII character set (the first 128 characters). A character literal in Haskell has type Char.

To convert a Char to or from the corresponding Int value defined by Unicode, use toEnum and fromEnum from the Enum class respectively (or equivalently ord and chr).

Character classification

Unicode characters are divided into letters, numbers, marks, punctuation, symbols, separators (including spaces) and others (including control characters).

isControl :: Char -> Bool Source

Selects control characters, which are the non-printing characters of the Latin-1 subset of Unicode.

isSpace :: Char -> Bool Source

Returns True for any Unicode space character, and the control characters \t, \n, \r, \f, \v.

isLower :: Char -> Bool Source

Selects lower-case alphabetic Unicode characters (letters).

isUpper :: Char -> Bool Source

Selects upper-case or title-case alphabetic Unicode characters (letters). Title case is used by a small number of letter ligatures like the single-character form of Lj.

isAlpha :: Char -> Bool Source

Selects alphabetic Unicode characters (lower-case, upper-case and title-case letters, plus letters of caseless scripts and modifiers letters). This function is equivalent to isLetter.

isAlphaNum :: Char -> Bool Source

Selects alphabetic or numeric digit Unicode characters.

Note that numeric digits outside the ASCII range are selected by this function but not by isDigit. Such digits may be part of identifiers but are not used by the printer and reader to represent numbers.

isPrint :: Char -> Bool Source

Selects printable Unicode characters (letters, numbers, marks, punctuation, symbols and spaces).

isDigit :: Char -> Bool Source

Selects ASCII digits, i.e. '0'..'9'.

isOctDigit :: Char -> Bool Source

Selects ASCII octal digits, i.e. '0'..'7'.

isHexDigit :: Char -> Bool Source

Selects ASCII hexadecimal digits, i.e. '0'..'9', 'a'..'f', 'A'..'F'.

isLetter :: Char -> Bool Source

Selects alphabetic Unicode characters (lower-case, upper-case and title-case letters, plus letters of caseless scripts and modifiers letters). This function is equivalent to isAlpha.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• UppercaseLetter
• LowercaseLetter
• TitlecaseLetter
• ModifierLetter
• OtherLetter

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Letter".

Examples

>>> isLetter 'a'
True
>>> isLetter 'A'
True
>>> isLetter '0'
False
>>> isLetter '%'
False
>>> isLetter '♥'
False
>>> isLetter '\31'
False

>>> let chars = [(chr 0)..]
>>> let letters = map isLetter chars
>>> let alphas = map isAlpha chars
>>> letters == alphas
True

isMark :: Char -> Bool Source

Selects Unicode mark characters, for example accents and the like, which combine with preceding characters.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• NonSpacingMark
• SpacingCombiningMark
• EnclosingMark

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Mark".

Examples

>>> isMark 'a'
False
>>> isMark '0'
False

>>> map isMark "ò"
[False,True]

>>> isMark '✓'
False

isNumber :: Char -> Bool Source

Selects Unicode numeric characters, including digits from various scripts, Roman numerals, et cetera.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• DecimalNumber
• LetterNumber
• OtherNumber

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Number".

Examples

>>> isNumber 'a'
False
>>> isNumber '%'
False
>>> isNumber '3'
True

>>> and $ map isNumber ['0'..'9']
True

>>> isNumber 'Ⅸ'
True

isPunctuation :: Char -> Bool Source

Selects Unicode punctuation characters, including various kinds of connectors, brackets and quotes.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• ConnectorPunctuation
• DashPunctuation
• OpenPunctuation
• ClosePunctuation
• InitialQuote
• FinalQuote
• OtherPunctuation

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Punctuation".

Examples

>>> isPunctuation 'a'
False
>>> isPunctuation '7'
False
>>> isPunctuation '♥'
False
>>> isPunctuation '"'
True
>>> isPunctuation '?'
True
>>> isPunctuation '—'
True

isSymbol :: Char -> Bool Source

Selects Unicode symbol characters, including mathematical and currency symbols.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• MathSymbol
• CurrencySymbol
• ModifierSymbol
• OtherSymbol

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Symbol".

Examples

>>> isSymbol 'a'
False
>>> isSymbol '6'
False
>>> isSymbol '='
True

>>> isSymbol '+'
True
>>> isSymbol '-'
False

isSeparator :: Char -> Bool Source

Selects Unicode space and separator characters.

This function returns True if its argument has one of the following GeneralCategorys, or False otherwise:

• Space
• LineSeparator
• ParagraphSeparator

These classes are defined in the Unicode Character Database, part of the Unicode standard. The same document defines what is and is not a "Separator".

Examples

>>> isSeparator 'a'
False
>>> isSeparator '6'
False
>>> isSeparator ' '
True

>>> isSeparator '\n'
False
>>> isSeparator '\t'
False

>>> isSeparator '\160'
True

Subranges

isAscii :: Char -> Bool Source

Selects the first 128 characters of the Unicode character set, corresponding to the ASCII character set.

isLatin1 :: Char -> Bool Source

Selects the first 256 characters of the Unicode character set, corresponding to the ISO 8859-1 (Latin-1) character set.

isAsciiUpper :: Char -> Bool Source

Selects ASCII upper-case letters, i.e. characters satisfying both isAscii and isUpper.

isAsciiLower :: Char -> Bool Source

Selects ASCII lower-case letters, i.e. characters satisfying both isAscii and isLower.

Unicode general categories

data GeneralCategory Source

Unicode General Categories (column 2 of the UnicodeData table) in the order they are listed in the Unicode standard (the Unicode Character Database, in particular).

Examples

>>> :t OtherLetter
OtherLetter :: GeneralCategory

>>> UppercaseLetter == UppercaseLetter
True
>>> UppercaseLetter == LowercaseLetter
False

>>> NonSpacingMark <= MathSymbol
True

>>> enumFromTo ModifierLetter SpacingCombiningMark
[ModifierLetter,OtherLetter,NonSpacingMark,SpacingCombiningMark]

>>> read "DashPunctuation" :: GeneralCategory
DashPunctuation
>>> read "17" :: GeneralCategory
*** Exception: Prelude.read: no parse

>>> show EnclosingMark
"EnclosingMark"

>>> minBound :: GeneralCategory
UppercaseLetter
>>> maxBound :: GeneralCategory
NotAssigned

>>> import Data.Ix ( index )
>>> index (OtherLetter,Control) FinalQuote
12
>>> index (OtherLetter,Control) Format
*** Exception: Error in array index

generalCategory :: Char -> GeneralCategory Source

The Unicode general category of the character. This relies on the Enum instance of GeneralCategory, which must remain in the same order as the categories are presented in the Unicode standard.

Examples

>>> generalCategory 'a'
LowercaseLetter
>>> generalCategory 'A'
UppercaseLetter
>>> generalCategory '0'
DecimalNumber
>>> generalCategory '%'
OtherPunctuation
>>> generalCategory '♥'
OtherSymbol
>>> generalCategory '\31'
Control
>>> generalCategory ' '
Space

Case conversion

toUpper :: Char -> Char Source

Convert a letter to the corresponding upper-case letter, if any. Any other character is returned unchanged.

toLower :: Char -> Char Source

Convert a letter to the corresponding lower-case letter, if any. Any other character is returned unchanged.

toTitle :: Char -> Char Source

Convert a letter to the corresponding title-case or upper-case letter, if any. (Title case differs from upper case only for a small number of ligature letters.) Any other character is returned unchanged.

Single digit characters

digitToInt :: Char -> Int Source

Convert a single digit Char to the corresponding Int. This function fails unless its argument satisfies isHexDigit, but recognises both upper- and lower-case hexadecimal digits (that is, '0'..'9', 'a'..'f', 'A'..'F').

Examples

>>> map digitToInt ['0'..'9']
[0,1,2,3,4,5,6,7,8,9]

>>> map digitToInt ['a'..'f']
[10,11,12,13,14,15]
>>> map digitToInt ['A'..'F']
[10,11,12,13,14,15]

>>> digitToInt 'G'
*** Exception: Char.digitToInt: not a digit 'G'
>>> digitToInt '♥'
*** Exception: Char.digitToInt: not a digit '\9829'

intToDigit :: Int -> Char Source

Convert an Int in the range 0..15 to the corresponding single digit Char. This function fails on other inputs, and generates lower-case hexadecimal digits.

Numeric representations

ord :: Char -> Int Source

The fromEnum method restricted to the type Char.

chr :: Int -> Char Source

The toEnum method restricted to the type Char.

String representations

showLitChar :: Char -> ShowS Source

Convert a character to a string using only printable characters, using Haskell source-language escape conventions. For example:

showLitChar '\n' s  =  "\\n" ++ s

lexLitChar :: ReadS String Source

Read a string representation of a character, using Haskell source-language escape conventions. For example:

lexLitChar  "\\nHello"  =  [("\\n", "Hello")]

readLitChar :: ReadS Char Source

Read a string representation of a character, using Haskell source-language escape conventions, and convert it to the character that it encodes. For example:

readLitChar "\\nHello"  =  [('\n', "Hello")]