TAL Programmer's Guide

Creating Source Files
Getting Started
096254 Tandem Computers Incorporated 2–3
System Procedures System procedures are procedures provided by the operating system. Declarations for
system procedures are located in the EXTDECS files. You can, for instance, use system
procedures when your program needs to:
Perform input/output operations
Manage processes
Communicate with other processes
Interface with the command interpreter (TACL)
Interface with terminals, printers, magnetic tapes, and card readers
Send operator messages
Provide fault tolerance
Handle traps
Appendixes A and B contain examples that include input/output and other system
procedures. For information on how to use the system procedures, however, see the
Guardian Programmer’s Guide and the Guardian Procedure Calls Reference Manual.
The sample source file includes one system procedure, INITIALIZER, which processes
the startup message.
Procedures Procedures contain the executable parts of a TAL program. Procedures can contain
data declarations, statements, and subprocedures.
A TAL program consists of one or more procedures. The program must include a
MAIN procedure (a procedure that has the MAIN attribute). The MAIN procedure
executes first when you run the program.
The sample source file consists of one procedure, named MYPROC. This procedure
has the MAIN attribute and contains data declarations and statements.
Data Declarations Data declarations associate identifiers with memory locations and allocate storage
space for variables. Variables contain data that can change during program execution.
You can initialize variables with values when you declare the variables, or you can
assign values to them later in assignment statements.
The sample source file includes data declarations for variables named VAR1, VAR2,
and TOTAL. These variables are not initialized when they are declared; they are
assigned values later in the source file.