Data.Char

The character type Char is an enumeration whose values represent Unicode (or equivalently ISO 10646) characters. This set extends the ISO 8859-1 (Latin-1) character set (the first 256 charachers), 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

MArray IOUArray Char IO

IArray (IOToDiffArray IOUArray) Char

MArray (STUArray s) Char (ST s)

Ix ix => Eq (UArray ix Char)

Ix ix => Ord (UArray ix Char)

(Ix ix, Show ix) => Show (DiffUArray ix Char)

(Ix ix, Show ix) => Show (UArray ix Char)

type String = [Char]

A String is a list of characters. String constants in Haskell are values of type String.

Character classification

Unicode characters are divided into letters, numbers, marks, punctuation, symbols, separators (including spaces) and others (including control characters). The full set of Unicode character attributes is not accessible in this library.

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.

isControl :: Char -> Bool

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

isSpace :: Char -> Bool

Selects white-space characters in the Latin-1 range. (In Unicode terms, this includes spaces and some control characters.)

isLower :: Char -> Bool

Selects lower-case alphabetic Unicode characters (letters).

isUpper :: Char -> Bool

Selects alphabetic Unicode characters (letters) that are not lower-case. (In Unicode terms, this includes letters in upper and title cases, as well as modifier letters and other letters.)

isAlpha :: Char -> Bool

Selects alphabetic Unicode characters (letters).

Note: the Haskell 98 definition of isAlpha is:

   isAlpha c = isUpper c || isLower c

the implementation here diverges from the Haskell 98 definition in the sense that Unicode alphabetic characters which are neither upper nor lower case will still be identified as alphabetic by isAlpha.

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'.

Case conversion

toUpper :: Char -> Char

Convert a letter to the corresponding upper-case letter, leaving any other character unchanged. Any Unicode letter which has an upper-case equivalent is transformed.

toLower :: Char -> Char

Convert a letter to the corresponding lower-case letter, leaving any other character unchanged. Any Unicode letter which has a lower-case equivalent is transformed.

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 (i.e. '0'..'9', 'a'..'f', 'A'..'F').

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")]

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