In application programs, sets break points where execution is to be halted.
The HALT command suspends execution of the currently executing application program and displays the HALT prompt (>>) at the terminal. You can then enter any command, including a call to another program.
The SET SINGLESTEP ON command causes the HALT command to be automatically executed after each command in the currently executing program.
If executed at the HALT prompt, BYE, RETURN, STOP, and global SET commands act in the usual manner. Local SET commands (e.g., LEXTRACE, RUNTIME, FLOW) is applied to the suspended program when it resumes.
If desired, you can redefine HALT to perform any useful function.
To re-define HALT, first ERASE the HALT program. Next, change the definition of HALT in the Documents EntitySet: make HALT correspond to a disk file called HALT.DOC. CREATE HALT again, ensuring that HALT.DOC contains the commands to perform the desired function.
For example, if you wanted to track memory use, HALT.DOC can contain the line:
system ” chkdsk”
% this command shows memory use
If you were to issue the command SET SINGLESTEP ON, the new version of HALT would be executed after every command, giving you a continuous record of disk and memory use.
halt % at >> prompt, you can turn on tracing,
% output variables, etc.