7.1 Characters

The module Char contains procedures operating on characters. Characters are integers between 0 and 255, used for building strings. For the encoding of characters by integers, we use the ISO 8859-1 standard [ISO87]. The functionality provided by this module is similar to the ctype.h module of ANSI C, see for instance [KR88].

The procedures described herein can be used to compute with strings by using the generic procedures of the list module (see Section 6.3). For example,

{Filter "r E!m O\nv7E" Char.isAlpha}

keeps only the letters of the given string and returns the string "rEmOvE".

IsChar

{Char.is +X ?B}

tests whether X is a character, i. e., an integer between 0 and 255 inclusively.

isLower

{Char.isLower +Char ?B}

tests whether Char encodes a lower-case letter.

isUpper

{Char.isUpper +Char ?B}

tests whether Char encodes an upper-case letter.

isDigit

{Char.isDigit +Char ?B}

tests whether Char encodes a digit.

isSpace

{Char.isSpace +Char ?B}

tests whether Char encodes a white space character, i. e., either a space, a form feed (&\f), a newline (&\n), a carriage return (&\r), a tab (&\t), a vertical tab (&\v) or a non-breaking space (&\240).

isPunct

{Char.isPunct +Char ?B}

tests whether Char encodes a punctuation character, i. e., a visible character, which is not a space, a digit, or a letter.

isCntrl

{Char.isCntrl +Char ?B}

tests whether Char encodes a control character.

isAlpha

{Char.isAlpha +Char ?B}

tests whether Char encodes a letter.

isAlNum

{Char.isAlNum +Char ?B}

tests whether Char encodes a letter or a digit.

isGraph

{Char.isGraph +Char ?B}

tests whether Char encodes a visible character.

isPrint

{Char.isPrint +Char ?B}

tests whether Char is a visible character or either the space or non-breaking space character.

isXDigit

{Char.isXDigit +Char ?B}

tests whether Char is a hexadecimal digit.

type

{Char.type +Char ?A}

maps Char to its simple type A, i. e., one of the atoms lower, upper, digit, space, punct, or other.

toLower

{Char.toLower +Char1 ?Char2}

returns the corresponding lower-case letter if Char1 is an upper-case letter, otherwise Char1 itself.

toUpper

{Char.toUpper +Char1 ?Char2}

returns the corresponding upper-case letter if Char1 is a lower-case letter, otherwise Char1 itself.

toAtom

{Char.toAtom +Char ?A}

maps Char to the corresponding atom A. If Char is zero, A will be the empty atom ''.