In addition, there is the library library(ctype) providing compatibility to some other Prolog systems. The predicates of this library are defined in terms of code_type/2.
char_type(?Char, ?Type)
Tests or generates alternative Types or Chars. The character-types are inspired by the standard C <ctype.h> primitives.
alnum
Char is a letter (upper- or lowercase) or digit.
alpha
Char is a letter (upper- or lowercase).
csym
Char is a letter (upper- or lowercase), digit or the underscore (_). These are valid C- and Prolog symbol characters.
csymf
Char is a letter (upper- or lowercase) or the underscore (_). These are valid first characters for C- and Prolog symbols
ascii
Char is a 7-bits ASCII character (0..127).
white
Char is a space or tab. E.i. white space inside a line.
cntrl
Char is an ASCII control-character (0..31).
digit
Char is a digit.
digit(Weigth)
Char is a digit with value Weigth. I.e. char_type(X, digit(6) yields X = '6'. Useful for parsing numbers.
xdigit(Weigth)
Char is a haxe-decimal digit with value Weigth. I.e. char_type(a, xdigit(X) yields X = '10'. Useful for parsing numbers.
graph
Char produces a visible mark on a page when printed. Note that the space is not included!
lower
Char is a lower-case letter.
lower(Upper)
Char is a lower-case version of Upper. Only true if Char is lowercase and Upper uppercase.
to_lower(Upper)
Char is a lower-case version of Upper. For non-letters, or letter without case, Char and Lower are the same. See also upcase_atom/2 and downcase_atom/2.
upper
Char is an upper-case letter.
upper(Lower)
Char is an upper-case version of Lower. Only true if Char is uppercase and Lower lowercase.
to_upper(Lower)
Char is an upper-case version of Lower. For non-letters, or letter without case, Char and Lower are the same. See also upcase_atom/2 and downcase_atom/2.
punct
Char is a punctuation character. This is a graph character that is not a letter or digit.
space
Char is some form of layout character (tab, vertical-tab, newline, etc.).
end_of_file
Char is -1.
end_of_line
Char ends a line (ASCII: 10..13).
newline
Char is a the newline character (10).
period
Char counts as the end of a sentence (.,!,?).
quote
Char is a quote-character (", ', `).
paren(Close)
Char is an open-parenthesis and Close is the corresponding close-parenthesis.
code_type(?Code, ?Type)
As char_type/2, but uses character-codes rather than one-character atoms. Please note that both predicates are as flexible as possible. They handle either representation if the argument is instantiated and only will instantiate with an integer code or one-character atom depending of the version used. See also the prolog-flag double_quotes, atom_chars/2 and atom_codes/2.
