A Pascal program is composed entirely of lexical elements. These elements are individual symbols, such as arithmetic operators, or they may be words that have special meanings in Pascal. The basic unit of any lexical element is a character, which must be a member of the ASCII character set. The words used in a Pascal program are combinations of alphabetic and numeric characters and occasionally a dollar sign ($), an underscore (_), or a percent sign (%). Some words are reserved for the names of executable statements, operations, and predefined data structures. Other words in a Pascal program are identifiers. Predeclared identifiers represent routines and data types provided by VSI Pascal. Other identifiers are created by the use to name programs, symbolic constants, variables, and any necessary program elements that have not already been named.
1 – Character Set
VSI Pascal uses the extended American Standard Code for
Information Interchange (ASCII) character set. The is extended
ASCII character set contains 256 characters, which include the
following:
o Uppercase letters A through Z and lowercase letters a
through z
o Integers 0 through 9
o Special characters, such as the ampersand (&), question mark
(?), and equal sign (=)
o Nonprinting characters, such as the space, tab, line feed,
carriage return, and form feed (use of these characters may
improve the legibility of your programs)
o Extended, unspecified characters with numeric codes from 128
to 255
The VSI Pascal compiler does not distinguish between uppercase
and lowercase letters except when they appear inside
apostrophes.
For a complete listing of the ASCII character set, see the "HP
Pascal Language Reference Manual."
2 – Special Symbols
Special symbols represent delimiters, operators, and other
syntactic elements. Some symbols are composed of more that one
character; you cannot place a space between the characters of
these special symbols. Examples of special symbols include the
apostrophe ('), the assignment operator (:=) and the not equal
sign (<>).
3 – Reserved Words
Reserved words are words that are reserved for the names of statements, data types, directives, identifiers, specifiers, statements, and operators. You cannot redefine these identifiers. Examples of reserved words include AND, END, NOT, IF, and WHILE. Redefinable reserved words are used to name operators and identifiers. You can redeclare these words, but, if you do, the language feature becomes unavailable within the block in which you redeclare the word. The redefinable reserved words are AND_THEN, BREAK, CONTINUE, MODULE, OR_ELSE, OTHERWISE, REM, RETURN, VALUE, and VARYING.
4 – Identifiers
An identifier is a combination of letters, digits, dollar signs
($), and underscores (_) that conform to the following
restrictions:
o An identifier cannot start with a digit.
o An identifier cannot contain any space or special symbols.
o The first 31 characters must denote a unique name within the
block in which the identifier is declared. An identifier
longer than 31 characters generates a warning message; the
compiler ignores characters beyond the thirty-first
character. An identifier cannot start or end with an
underscore, nor can two adjacent
4.1 – Predeclared Identifiers
Predeclared identifiers name data types, symbolic constants and file variables, procedures, and functions. You can redefine a predeclared identifier, but, if you do, the original declaration becomes unavailable within the block in which you redeclared the word. Examples of predeclared identifiers include ADDRESS, COS, INTEGER, SQR and TRUE.
4.2 – User Defined Identifiers
User identifiers denote the names of programs, modules, symbolic constants, variables, procedures, functions, program sections, and user-defined types. They represent significant data structures, or values and actions that are not represented by reserved words, predeclared identifiers, or special symbols.