Mercury Programming/Types

Types

Char

A value of type 'char' is a single unicode character (implemented using UTF8 encoding and so may occupy 1 to 4 bytes). There are several ways to specify a 'char' as a literal value:

• As an ordinary character between single quotes, for example 'a' - unless:
  • the character is a single quote, in which case use 4 single quotes: '''', or use 3 single quotes and with a backslash as the second character: '\''.
  • the character is a backslash, in which case use 2 backslashes between single quotes: '\\'.
  • the character is the double quote, in which case put it between single quotes: '”', or give it a leading backslash and put them between single quotes: '\”'.

• As a hexadecimal value giving the Unicode code point (see Unicode) of the required character; the hexadecimal value must have a leading 'x', placed between '\' characters, which are in turn placed between single quotes, for example '\x63\' (equivalent to the character 'c').

• As an octal value giving the Unicode code point of the required character; the octal value must be placed between '\' characters, which are in turn placed between single quotes, for example '\251\' (equivalent to the character '©').

• As a 4 digit hexadecimal value giving the Unicode code point of the required character; the value must be prefixed with '\u', and the result placed between single quotes, for example '\u00B5' (equivalent to the Greek lower case character μ).

• As an 8 digit hexadecimal value giving the Unicode code point of the required character; the value must be prefixed with '\U', and the result placed between single quotes, for example '\U000000B1' (equivalent to the character '±'). Note that the highest allowed value is '\U0010FFFF'.

• Several special characters can be specified as shown in the table below:

Character	Specified Using
beep	'\a'
backspace	'\b'
carriage return	'\r'
form feed	'\f'
tab	'\t'
new line	'\n'
vertical tab	'\v'

A simple Mercury program demonstrating 'char' literals is in Section A.1