"It can do whatever you want." No, it can only do those things that the PL/I language provides for. There is no time machine function. If you want to be able to view past values of the variables then somebody must record those values. By the time the ON unit is invoked it's too late.
What you write about later is no code in the ON unit, but code in the rest of the program. Adding code to record the value before and after each assignment statement still does not give you the functionality of a debugger. You still need code to scroll forward and back in time. -- Shmuel (Seymour J.) Metz http://mason.gmu.edu/~smetz3 ________________________________________ From: IBM Mainframe Assembler List <ASSEMBLER-LIST@listserv.uga.edu> on behalf of Robin Vowels <robi...@dodo.com.au> Sent: Saturday, February 10, 2018 7:25 AM To: ASSEMBLER-LIST@listserv.uga.edu Subject: Re: Fair comparison C vs HLASM From: "Seymour J Metz" <sme...@gmu.edu> Sent: Friday, February 09, 2018 6:41 AM > A traceback is not a trace. An ON unit can display *current* values of a > variable, It can do whatever you want. For example, you could stack the values of any given variable in the current procedure, and use the ON-unit to print some or all generations. Stacking can also be done for any variables in procedures called earlier, and their values displayed through an ON-unit in those procedures (use RESIGNAL). > not past values. I have no idea what you mean by "A trace is trivial with > PROCEDURENAME." PROCNAME returns the name of the current procedure. You can either write that out to a file, or stack it, to be retrieved later, along with values of any relevant variables. > or how it provides a complete history of the program's execution, much less > an interface for > viewing it selectively. Use it in each procedure, on entry. ________________________________________ From: IBM Mainframe Assembler List <ASSEMBLER-LIST@listserv.uga.edu> on behalf of Robin Vowels <robi...@dodo.com.au> Sent: Tuesday, February 6, 2018 7:30 PM To: ASSEMBLER-LIST@listserv.uga.edu Subject: Re: Fair comparison C vs HLASM From: "Seymour J Metz" <sme...@gmu.edu> Sent: Monday, February 05, 2018 7:21 AM > As an example, some debuggers log a trace of the program > and allow you to scroll the log back from the point of failure PL/I provides a traceback. Values of variables can be displayed via an ON-unit. A trace is trivial with PROCEDURENAME. > in order to track down when, where and how variables acquired unexpected > values. --- This email has been checked for viruses by Avast antivirus software. https://secure-web.cisco.com/1FE12FpsT12eYdkSTXv1V4oFjem1vAAIJO7u6-znXJTtyBxfwfQiGg_KjI-c6o3fV_wrVSv-iV0HvP9m8-1G74opcUk-1mdasWR8-uVaYeXz5TIJHMVyVs8H261w7Q5CmmLNw8AWyQ-7eWmryoENXe409DF5vYHdts5Ii6WU1O0l-Y2Qh_XYtonT9y0giQxQhCJg7hFJssvaw3oC_eb_VjUMumyPuzIMST96gGc7gRTSXjNBWaZfju6pZN6-jn8GvaRxqPuEsYdhNpPT1HoSzHH1XxJFGpwPZRPqzVcady6f4Kwb9PbcmHFVsn8t4eQa1bDJ95Wphi9qLGjA3YvB9GFuIsZn5kxurCZQJZC6zX79b8HFano1CjwF9TwL0ea-857vNY44iuvhxZqZmFDCM4zbGdr1Hfq4xS5ha5PBlMXZhTld8hM4v5SY31HTxueBK/https%3A%2F%2Fwww.avast.com%2Fantivirus
