Re: SLang debugger

["John E. Davis" <davis@xxxxxxxxxxxxx>]

SANGOI DINO <SANGOID@xxxxxxxxxxxxxxxxx> wrote:
>This is a tecnology preview version of SLang Debugger for Jed!

Very nice.

[...]
>I did this mostly as a "proof of concept", to see if it was possible to use
>bos_handler to create a debugger. More interpreter help is needed to build a
>real debugger, to be able to change variables in other scopes, for example
>(but I don't want to allow every script to do this, only the debugger, so is
>a complex thing to think about).

I added the bos/eos hooks with the hope that they would be eventually
be useful for a debugger.  Inspired by your work, this weekend I made
several internal changes to the interpreter to allow access to local
variables of any function on the stack-frame.

[...]
>I John likes the idea, this new array, Num_Args_Stack, and maybe
>Local_Variable_Frame (index for local variables in Local_Variable_Stack) may
>be unified in a structure array...

That is more or less what I did.

I was hoping to releases slang 2 next weekend but I have decided that
having a debugger is worth delaying the release for another week.

Here is a preview of what will be possible in the next slang2 snapshot.
Consider the script "t.sl":

  require ("glob");
  static variable T = NULL;
  define foo (pattern)
  {
     variable files = glob (pattern);
     message (files);
  }
  define main ()
  {
     variable pattern = T;
     foo (pattern);
  }
  main ();

Executing it with slsh yields an error:

  Unable to typecast Null_Type to String_Type
  /usr/local/share/slsh/glob.sl:16:needs_globbing:Type Mismatch

Now insert the lines:

  require ("debugger"); 
  run_debugger ();

at the top of the file and execute the script again.  This time it
produces a prompt "(sdb)" where debugger commands may be entered;

  <top-level> at ./t.sl:3
  3 require ("glob");
  (sdb) help
  Commands:
    delete
    cont
    quit
    print
    where
    break
    up
    exit
    down
    step
    help
    watch
    finish
    list
    next
  (sdb) cont
  Received Type Mismatch error.  Entering the debugger
  needs_globbing at /usr/local/share/slsh/glob.sl:16
  16    return (path != str_delete_chars (path, "*?["));
  (sdb) print path
  NULL
  (sdb) up
  #1 /usr/local/share/slsh/glob.sl:51:glob
  51 	!if (needs_globbing (pat))
  (sdb) print pat
  NULL
  (sdb) up
  #2 ./t.sl:7:foo
  7    variable files = glob (pattern);
  (sdb) print pattern
  NULL
  (sdb) list
  2 enable_debug ();
  3 require ("glob");
  4 static variable T = NULL;
  5 define foo (pattern)
  6 {
  7    variable files = glob (pattern);
  8    message (files);
  9 }
  10 define main ()
  11 {
  12    variable pattern = T;
  (sdb) up
  #3 ./t.sl:13:main
  13    foo (pattern);
  (sdb) print pattern
  NULL
  (sdb) print T
  NULL
  (sdb) up
  #4 ./t.sl:15:<top-level frame>
  15 main ();
  (sdb) up
  Can't go up
  (sdb) quit

So, problem is that T is set to NULL.  Set it to "*" and run the
script again:

  <top-level> at ./t.sl:3
  3 require ("glob");
  (sdb) next
  4 static variable T = "*";
  (sdb) 
  15 main ();
  (sdb) step
  main at ./t.sl:12
  12    variable pattern = T;
  (sdb) next
  13    foo (pattern);
  (sdb) print pattern
  *
  (sdb) cont
  Received Type Mismatch error.  Entering the debugger
  8    message (files);
  (sdb) list
  3 require ("glob");
  4 static variable T = "*";
  5 define foo (pattern)
  6 {
  7    variable files = glob (pattern);
  8    message (files);
  9 }
  10 define main ()
  11 {
  12    variable pattern = T;
  13    foo (pattern);
  (sdb) print files
  String_Type[39]
  (sdb) print files[0]
  ./lib
  (sdb) print files[1]
  ./scripts
  (sdb) cont
  Unable to typecast Array_Type to String_Type
  ./t.sl:8:foo:Type Mismatch

As you can see, the second error is that an array was being passed to
the "message" function in line 8.

Thanks,
--John

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