[Netrexx-develop] interactive trace

[Marc R. <re...@gm...>]

I've submitted branch interactive-trace, an *experimental* *experiment* to mimic Classic Rexx interactive trace capabilities.

The new 'TRACE INT' instruction will intercept and pause execution during interpretation and present a '*->' prompt to the user.
Pressing [Enter] will interpret next clause
Typing '=' will reinterpret current clause
Typing '?' will show usage
Typing 'TRACE OFF' will stop interactive trace and will continue normally with next clause
Typing anything else is currently 'not supported'.

TRACE INT is only active when interpreting NetRexx code, otherwise a warning 'TRACE INT ignored when compiling' is shown.

An example:
<<
$ cat trace.nrx

class trace

    method main(args=String[]) static
      say 'interactively tracing..'
      trace int
      i=0
      say 'i='i
      do
        say 'Hello world'||'!'.copies(i)
      end
      trace off
      loop while i < 5
        trace int
        i=i+1
        say 'i='i
        say 'Hello world'||'!'.copies(i)
      end
>>

Sample run:
<<
$ nrc -exec trace
NetRexx portable processor 4.04-alpha build 1,400-20220530-2046
Copyright (c) RexxLA, 2011,2022.   All rights reserved.
Parts Copyright (c) IBM Corporation, 1995,2008.
Program trace.nrx
    === class trace ===
      function main(String[])
===== Exec: trace =====
interactively tracing..
   *->
      --- trace.nrx
    6 *=*     i=0
      >v> i "0"
   *->
    7 *=*     say 'i='i
      >>> "i=0"
i=0
   *-> trace off
Hello world
   *->
   14 *=*       i=i+1
      >v> i "1"
   *-> trace off
i=1
Hello world!
   *->
   14 *=*       i=i+1
      >v> i "2"
   *-> =
      *=*       i=i+1
      >v> i "3"
   *->
   15 *=*       say 'i='i
      >>> "i=3"
i=3
   *->
   16 *=*       say 'Hello world'||'!'.copies(i)
      >>> "3"
      >>> "Hello world!!!"
Hello world!!!
   *->
   12 *=*     loop while i < 5
      >>> "1"
   *-> trace off
   *->
   14 *=*       i=i+1
      >v> i "4"
   *-> trace off
i=4
Hello world!!!!
   *-> trace off
i=5
Hello world!!!!!
Processing of 'trace.nrx' complete
>>

Do not reinterprete a clause that changes 'level' depth:
<<
$ nrc -exec trace
NetRexx portable processor 4.04-alpha build 1,400-20220530-2046
Copyright (c) RexxLA, 2011,2022.   All rights reserved.
Parts Copyright (c) IBM Corporation, 1995,2008.
Program trace.nrx
    === class trace ===
      function main(String[])
===== Exec: trace =====
interactively tracing..
   *->
      --- trace.nrx
    6 *=*     i=0
      >v> i "0"
   *->
    7 *=*     say 'i='i
      >>> "i=0"
i=0
   *->
    8 *=*     do
   *->
    9 *=*       say 'Hello world'||'!'.copies(i)
      >>> "0"
      >>> "Hello world"
Hello world
   *->
   10 *=*     end
   *-> =
      *=*     end
   *-> =
      *=*     end
Exception in thread "main" java.lang.NullPointerException: Cannot read field "prev" because "<parameter1>.curlevel" is null
	at org.netrexx.process.RxInterpreter.poplevel(RxInterpreter.java:1590)
	at org.netrexx.process.NrEnd.interpret(NrEnd.java:174)
	at org.netrexx.process.RxInterpreter.runfree(RxInterpreter.java:1314)
	at org.netrexx.process.RxInterpreter.callMethod(RxInterpreter.java:1180)
	at org.netrexx.process.RxInterpreter.callMethod(RxInterpreter.java:835)
	at org.netrexx.process.RxTranslator.exec(RxTranslator.java:791)
	at org.netrexx.process.NetRexxC.process(NetRexxC.java:536)
	at org.netrexx.process.NetRexxC.main2(NetRexxC.java:345)
	at org.netrexx.process.NetRexxC.main2(NetRexxC.java:324)
	at org.netrexx.process.NetRexxC.main2(NetRexxC.java:320)
	at org.netrexx.process.NetRexxC.main(NetRexxC.java:174)
>>
As such, the code is to be considered experimental..

Pressing [Enter] without interfering with execution should not have other impact than 'pausing' execution.

Obviously, 'not supported' should be replaced by interpreting the provided 'trace' clause in the context of the current program with access to the current varpool.
Unfortunately, this is not trivial, at least with my understanding of Mike's code.

Marc