Previous Next Contents Index Doc Set Home


Lexical Elements

1

This chapter describes the symbols and words of a Pascal program. It contains the following sections:

Character Set

page 1

Special Symbols

page 2

Reserved Words

page 3

Identifiers

page 4

Comments

page 6

Character Set

Pascal uses the standard seven-bit ASCII character set, and the compiler distinguishes between uppercase and lowercase characters. For example, the following seven words are distinct from the predefined type integer:

Integer

INTEGer

INteger

INTEGEr

INTeger

INTEGER

INTEger

If you change the case of characters used in a word, the compiler does not recognize the word and gives an error.

The Pascal keywords and built-in procedure and function names are all in lowercase.

To map all keywords and identifiers to lowercase when you compile your program, use the following pc options:

-L

Maps all uppercase letters in keywords and identifiers to lowercase.

-s

Performs the same action as -L and also produces warning diagnostics for nonstandard constructs and extensions.

See the Pascal 4.2 User's Guide for a complete description of pc and its options.

Special Symbols

Pascal recognizes the following standard Pascal symbols and the nonstandard special symbols listed in Table 1-1.







+ - * / = < > [ ] . , :=





: ; ( ) <> <= >= .. ^







 










Table  1-1	 Nonstandard Special Symbols  






Symbol



Description



Example






~




Bitwise not operator




~ 4





&




Bitwise and operator




4 & 3





|




Bitwise or operator




4 | 3





!




Bitwise or operator




4 ! 3





#




Specifies an integer value in a base other than base 10.




p := 2#10111; { base 2 }
f := 8#76543; { base 8 }










Includes a file in the program.




#include "globals.h"
#include "math_p.h"










Indicates a preprocessor command




#ifdef DEBUGGING
writeln('Total :',i,sum);
#endif





%




Indicates a cppas compiler directive




%var one, two
%enable two

Reserved Words

Pascal reserves the standard words in Table 1-2. You cannot redefine a reserved word to represent another item.




Table  1-2	 Standard Reserved Words






Pascal Standard Reserved Words






and




file




mod




repeat





array




for




nil




set





begin




forward




not




then





case




function




of




to





const




goto




or




type





div




if




packed




until





do




in




procedure




var





downto




label




program




while





else




main




record




with
Pascal also reserves the nonstandard words in Table 1-3. These words are not treated as reserved words when you compile your program with any of the -s, -s0, -s1, -V0 or -V1 options.




Table  1-3	 Nonstandard Reserved Words






Pascal Nonstandard Reserved Words






define




private





extern




public





external




static





module




univ





otherwise

Identifiers

In Pascal, you can include a dollar sign ($) and underscore (_) in an identifier name. The $ and _ can occur in any position of the identifier name. However, you should avoid using these characters in the first position because they may conflict with system names.

Pascal predeclares the standard identifiers in Table 1-4 and the nonstandard identifiers in Table 1-5.




Table  1-4	 Predeclared Standard Identifiers






Pascal Predeclared Standard Identifiers






abs




false




page




sin





arctan




get




pred




sqr





boolean




input




put




sqrt





char




integer




read




succ





chr




ln




readln




text





cos




maxint




real




true





dispose




new




reset




trunc





eof




odd




rewrite




write





eoln




ord




round




writeln





exp




output















 











Table  1-5	 Predeclared Nonstandard Identifiers






Pascal Predeclared Nonstandard Identifiers






FALSE




exit




lor




seek





TRUE




expo




lshft




shortreal





addr




filesize




lsl




single





alfa




firstof




lsr




sizeof





append




flush




max




stlimit





argc




getenv




maxchar




stradd





argv




getfile




message




string





arshft




halt




min




substr





asl




in_range




minchar




sysclock





asr




index




minint




tab





assert




integer16




next




tell





bell




integer32




null




time





card




intset




open




trace





clock




land




pack




trim





close




lastof




random




univ_ptr





concat




length




remove




unpack





date




linelimit




return




varying





discard




lnot




rshft




wallclock





double




longreal




seed




xor
You can redefine a predeclared identifier to represent another item. For example, you could redefine the predefined identifier next, a statement that causes the program to skip to the next iteration of the current loop, as a variable.

Once you redefine an identifier, you cannot use it as originally defined in the program, as shown in the following example:






The Pascal program, pred_iden.p, redefines the predeclared identifier next as an integer variable.





program predefined_identifier;









var





    i: integer;





    next: integer;









begin





    for i := 1 to 10 do begin





      if i > 5 then begin





          next





      end





    end





end. { predefined_identifier }







 

















This program does not compile because next is declared as a variable, but used in its original definition as a statement.





hostname% pc pred_iden.p





Mon Feb 20 15:13:17 1995  pred_iden.p:





          10            next





E 18470-----------------^---  Replaced variable id with a 
procedure id





In program predefined_identifier:





E 18250 next improperly used on line 10







 













 Comments




In Pascal, you can specify a comment in either braces, quotation marks, a parenthesis/asterisk pair, or a slash/asterisk pair: 




{  This is a comment. }





(* This is a comment. *)





"  This is a comment. "





/* This is a comment. */




The symbols used to delimit a comment must match.  For example, a comment that starts with { must end with }, and a comment that starts with (* must end with *).



You can nest comments in Pascal, that is, include one type of comment delimiter inside another:




{ This is a valid (* comment within a comment. *) }





(* This is a valid " comment within a comment. " *)




You cannot nest the same kind of comments.  The following comments result in a compile-time error:




{  This is not a valid { comment within a comment. } }





(* This is not a valid (* comment within a comment. *) *)





"  This is not a valid " comment within a comment. " "





/* This is not a valid /* comment within a comment. */ */






 



Previous


Next

Contents

Index

Doc Set

Home