Data.Char

The Char type and associated operations.

Documentation

data Char :: *

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).

Instances

Bounded Char

Methods

minBound :: Char

maxBound :: Char

Enum Char

Methods

succ :: Char -> Char

pred :: Char -> Char

toEnum :: Int -> Char

fromEnum :: Char -> Int

enumFrom :: Char -> [Char]

enumFromThen :: Char -> Char -> [Char]

enumFromTo :: Char -> Char -> [Char]

enumFromThenTo :: Char -> Char -> Char -> [Char]

Eq Char

Methods

(==) :: Char -> Char -> Bool

(/=) :: Char -> Char -> Bool

Data Char

Methods

gfoldl :: (forall d b. Data d => c (d -> b) -> d -> c b) -> (forall g. g -> c g) -> Char -> c Char

gunfold :: (forall b r. Data b => c (b -> r) -> c r) -> (forall r. r -> c r) -> Constr -> c Char

toConstr :: Char -> Constr

dataTypeOf :: Char -> DataType

dataCast1 :: Typeable (* -> *) t => (forall d. Data d => c (t d)) -> Maybe (c Char)

dataCast2 :: Typeable (* -> * -> *) t => (forall d e. (Data d, Data e) => c (t d e)) -> Maybe (c Char)

gmapT :: (forall b. Data b => b -> b) -> Char -> Char

gmapQl :: (r -> r' -> r) -> r -> (forall d. Data d => d -> r') -> Char -> r

gmapQr :: (r' -> r -> r) -> r -> (forall d. Data d => d -> r') -> Char -> r

gmapQ :: (forall d. Data d => d -> u) -> Char -> [u]

gmapQi :: Int -> (forall d. Data d => d -> u) -> Char -> u

gmapM :: Monad m => (forall d. Data d => d -> m d) -> Char -> m Char

gmapMp :: MonadPlus m => (forall d. Data d => d -> m d) -> Char -> m Char

gmapMo :: MonadPlus m => (forall d. Data d => d -> m d) -> Char -> m Char

Ord Char

Methods

compare :: Char -> Char -> Ordering

(<) :: Char -> Char -> Bool

(<=) :: Char -> Char -> Bool

(>) :: Char -> Char -> Bool

(>=) :: Char -> Char -> Bool

max :: Char -> Char -> Char

min :: Char -> Char -> Char

Read Char

Methods

readsPrec :: Int -> ReadS Char

readList :: ReadS [Char]

readPrec :: ReadPrec Char

readListPrec :: ReadPrec [Char]

Show Char

Methods

showsPrec :: Int -> Char -> ShowS

show :: Char -> String

showList :: [Char] -> ShowS

Ix Char

Methods

range :: (Char, Char) -> [Char]

index :: (Char, Char) -> Char -> Int

unsafeIndex :: (Char, Char) -> Char -> Int

inRange :: (Char, Char) -> Char -> Bool

rangeSize :: (Char, Char) -> Int

unsafeRangeSize :: (Char, Char) -> Int

Generic Char

Associated Types

type Rep Char :: * -> *

Methods

from :: Char -> Rep Char x

to :: Rep Char x -> Char

Storable Char

Methods

sizeOf :: Char -> Int

alignment :: Char -> Int

peekElemOff :: Ptr Char -> Int -> IO Char

pokeElemOff :: Ptr Char -> Int -> Char -> IO ()

peekByteOff :: Ptr b -> Int -> IO Char

pokeByteOff :: Ptr b -> Int -> Char -> IO ()

peek :: Ptr Char -> IO Char

poke :: Ptr Char -> Char -> IO ()

IsChar Char

Methods

toChar :: Char -> Char

fromChar :: Char -> Char

PrintfArg Char

Methods

formatArg :: Char -> FieldFormatter

parseFormat :: Char -> ModifierParser

IsString [Char]

Methods

fromString :: String -> [Char]

type Rep Char

Character classification

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

isControl :: Char -> Bool

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

isSpace :: Char -> Bool

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

isLower :: Char -> Bool

Selects lower-case alphabetic Unicode characters (letters).

isUpper :: Char -> Bool

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

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

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

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

isDigit :: Char -> Bool

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

isOctDigit :: Char -> Bool

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

isHexDigit :: Char -> Bool

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

isLetter :: Char -> Bool

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

Basic usage:

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

Ensure that isLetter and isAlpha are equivalent.

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

isMark :: Char -> Bool

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

Basic usage:

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

Combining marks such as accent characters usually need to follow another character before they become printable:

>>> map isMark "ò"
[False,True]

Puns are not necessarily supported:

>>> isMark '✓'
False

isNumber :: Char -> Bool

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

Basic usage:

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

ASCII '0' through '9' are all numbers:

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

Unicode Roman numerals are "numbers" as well:

>>> isNumber 'Ⅸ'
True

isPunctuation :: Char -> Bool

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

Basic usage:

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

isSymbol :: Char -> Bool

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

Basic usage:

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

The definition of "math symbol" may be a little counter-intuitive depending on one's background:

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

isSeparator :: Char -> Bool

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

Basic usage:

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

Warning: newlines and tab characters are not considered separators.

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

But some more exotic characters are (like HTML's  ):

>>> isSeparator '\160'
True

Subranges

isAscii :: Char -> Bool

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

isLatin1 :: Char -> Bool

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

isAsciiUpper :: Char -> Bool

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

isAsciiLower :: Char -> Bool

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

Unicode general categories

data GeneralCategory

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

Basic usage:

>>> :t OtherLetter
OtherLetter :: GeneralCategory

Eq instance:

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

Ord instance:

>>> NonSpacingMark <= MathSymbol
True

Enum instance:

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

Read instance:

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

Show instance:

>>> show EnclosingMark
"EnclosingMark"

Bounded instance:

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

Ix instance:

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

Constructors

UppercaseLetter

Lu: Letter, Uppercase

LowercaseLetter

Ll: Letter, Lowercase

TitlecaseLetter

Lt: Letter, Titlecase

ModifierLetter

Lm: Letter, Modifier

OtherLetter

Lo: Letter, Other

NonSpacingMark

Mn: Mark, Non-Spacing

SpacingCombiningMark

Mc: Mark, Spacing Combining

EnclosingMark

Me: Mark, Enclosing

DecimalNumber

Nd: Number, Decimal

LetterNumber

Nl: Number, Letter

OtherNumber

No: Number, Other

ConnectorPunctuation

Pc: Punctuation, Connector

DashPunctuation

Pd: Punctuation, Dash

OpenPunctuation

Ps: Punctuation, Open

ClosePunctuation

Pe: Punctuation, Close

InitialQuote

Pi: Punctuation, Initial quote

FinalQuote

Pf: Punctuation, Final quote

OtherPunctuation

Po: Punctuation, Other

MathSymbol

Sm: Symbol, Math

CurrencySymbol

Sc: Symbol, Currency

ModifierSymbol

Sk: Symbol, Modifier

OtherSymbol

So: Symbol, Other

Space

Zs: Separator, Space

LineSeparator

Zl: Separator, Line

ParagraphSeparator

Zp: Separator, Paragraph

Control

Cc: Other, Control

Format

Cf: Other, Format

Surrogate

Cs: Other, Surrogate

PrivateUse

Co: Other, Private Use

NotAssigned

Cn: Other, Not Assigned

Instances

Bounded GeneralCategory

Methods

minBound :: GeneralCategory

maxBound :: GeneralCategory

Enum GeneralCategory

Methods

succ :: GeneralCategory -> GeneralCategory

pred :: GeneralCategory -> GeneralCategory

toEnum :: Int -> GeneralCategory

fromEnum :: GeneralCategory -> Int

enumFrom :: GeneralCategory -> [GeneralCategory]

enumFromThen :: GeneralCategory -> GeneralCategory -> [GeneralCategory]

enumFromTo :: GeneralCategory -> GeneralCategory -> [GeneralCategory]

enumFromThenTo :: GeneralCategory -> GeneralCategory -> GeneralCategory -> [GeneralCategory]

Eq GeneralCategory

Methods

(==) :: GeneralCategory -> GeneralCategory -> Bool

(/=) :: GeneralCategory -> GeneralCategory -> Bool

Ord GeneralCategory

Methods

compare :: GeneralCategory -> GeneralCategory -> Ordering

(<) :: GeneralCategory -> GeneralCategory -> Bool

(<=) :: GeneralCategory -> GeneralCategory -> Bool

(>) :: GeneralCategory -> GeneralCategory -> Bool

(>=) :: GeneralCategory -> GeneralCategory -> Bool

max :: GeneralCategory -> GeneralCategory -> GeneralCategory

min :: GeneralCategory -> GeneralCategory -> GeneralCategory

Read GeneralCategory

Methods

readsPrec :: Int -> ReadS GeneralCategory

readList :: ReadS [GeneralCategory]

readPrec :: ReadPrec GeneralCategory

readListPrec :: ReadPrec [GeneralCategory]

Show GeneralCategory

Methods

showsPrec :: Int -> GeneralCategory -> ShowS

show :: GeneralCategory -> String

showList :: [GeneralCategory] -> ShowS

Ix GeneralCategory

Methods

range :: (GeneralCategory, GeneralCategory) -> [GeneralCategory]

index :: (GeneralCategory, GeneralCategory) -> GeneralCategory -> Int

unsafeIndex :: (GeneralCategory, GeneralCategory) -> GeneralCategory -> Int

inRange :: (GeneralCategory, GeneralCategory) -> GeneralCategory -> Bool

rangeSize :: (GeneralCategory, GeneralCategory) -> Int

unsafeRangeSize :: (GeneralCategory, GeneralCategory) -> Int

generalCategory :: Char -> GeneralCategory

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

Basic usage:

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

Case conversion

toUpper :: Char -> Char

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

toLower :: Char -> Char

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

toTitle :: Char -> Char

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

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

Characters '0' through '9' are converted properly to 0..9:

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

Both upper- and lower-case 'A' through 'F' are converted as well, to 10..15.

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

Anything else throws an exception:

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

intToDigit :: Int -> Char

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

The fromEnum method restricted to the type Char.

chr :: Int -> Char

The toEnum method restricted to the type Char.

String representations

showLitChar :: Char -> ShowS

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

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

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

readLitChar :: ReadS Char

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")]