All the symbols you can see on a computer, and some you
cannot see, are known as characters. The alphabet
consists of the characters A
to Z
and a
to
z
. The digits comprise the characters 0
to 9
.
Every computer recognises a particular set of characters. The
character set recognised by a68toc
is ASCII (which stands for American
Standard Code for Information Interchange). The mode of a character is
CHAR (read “car” because it is short for
character). A character is denoted by placing it between quote
characters. Thus the denotation of the lower-case a is "a"
.
Here are some character denotations:
"a" "A" "3" ";" "\" "'" """" " "
Note that quote characters are doubled in their denotations. The
third denotation is "3"
. This value has mode CHAR
.
The denotation 3
has mode INT
: the two values are quite
distinct, and one is not a synonym for the other. The last
denotation is that of the space character.
Here are some identity declarations for values of mode
CHAR
:
CHAR a = "A", zed = "z"; CHAR tilde = "~"
Note that the two sets of identity declarations are separated by a
semicolon, but the declaration for tilde
is not followed
by a semicolon. This is because the semicolon
; is not a terminator; it is an action.
Identity declarations do not yield any value.
An identity declaration is a phrase. Phrases
are either identity declarations or units. When a phrase is
elaborated, if it is a unit, it will yield a value.
That is, after elaboration, a value will be available for further use
if required. Again, this may not make much sense now, but it will
become clearer as you learn the language.
Here is a piece of program with identity declarations for an
INT
and a CHAR
:2.1
INT ninety nine=99 , CHAR x = "X"
The compiler recognises 512 distinct values of mode
CHAR
, but most of them can only occur in denotations. The
space is declared as blank in the standard
prelude.
8
(not the integer 8). AnsSian Mountbatten 2012-01-19