OS2::REXX(3pm)

NAME
OS2::REXX - access to DLLs with REXX calling convention and REXX runtime.

  NOTE
By default, the REXX variable pool is not available, neither to Perl, nor to external REXX functions. To enable it, you need to put your code inside "REXX_call" function. REXX functions which do not use variables may be usable even without "REXX_call" though.

SYNOPSIS
        use OS2::REXX;
        $ydb = load OS2::REXX "ydbautil" or die "Cannot load: $!";
        @pid = $ydb->RxProcId();
        REXX_call {
          tie $s, OS2::REXX, "TEST";
          $s = 1;
        };

DESCRIPTION

  Load REXX DLL
        $dll = load OS2::REXX NAME [, WHERE];

NAME is DLL name, without path and extension.

Directories are searched WHERE first (list of dirs), then environment paths PERL5REXX, PERLREXX, PATH or, as last resort, OS/2-ish search is performed in default DLL path (without adding paths and extensions).

The DLL is not unloaded when the variable dies.

Returns DLL object reference, or undef on failure.

  Define function prefix:
        $dll->prefix(NAME);

Define the prefix of external functions, prepended to the function names used within your program, when looking for the entries in the DLL.

  Example
                $dll = load OS2::REXX "RexxBase";
                $dll->prefix("RexxBase_");
                $dll->Init();

is the same as

                $dll = load OS2::REXX "RexxBase";
                $dll->RexxBase_Init();

  Define queue:
        $dll->queue(NAME);

Define the name of the REXX queue passed to all external functions of this module. Defaults to "SESSION".

Check for functions (optional):

        BOOL = $dll->find(NAME [, NAME [, ...]]);

Returns true if all functions are available.

  Call external REXX function:
        $dll->function(arguments);

Returns the return string if the return code is 0, else undef. Dies with error message if the function is not available.

Accessing REXX-runtime
While calling functions with REXX signature does not require the presence of the system REXX DLL, there are some actions which require REXX-runtime present. Among them is the access to REXX variables by name.

One enables REXX runtime by bracketing your code by

        REXX_call BLOCK;

(trailing semicolon required!) or

        REXX_call \&subroutine_name;

Inside such a call one has access to REXX variables (see below).

An alternative way to execute code inside a REXX compartment is

        REXX_eval EXPR;
        REXX_eval_with EXPR,
                subroutine_name_in_REXX => \&Perl_subroutine

Here "EXPR" is a REXX code to run; to execute Perl code one needs to put it inside Perl_subroutine(), and call this subroutine from REXX, as in

        REXX_eval_with <<EOE, foo => sub { 123 * shift };
          say foo(2)
        EOE

If one needs more Perl subroutines available, one can "import" them into REXX from inside Perl_subroutine(); since REXX is not case-sensitive, the names should be uppercased.

        use OS2::REXX 'register';

        sub BAR { 123 + shift}
        sub BAZ { 789 }
        sub importer { register qw(BAR BAZ) }

        REXX_eval_with <<'EOE', importer => \&importer;
          call importer
          say bar(34)
          say baz()
        EOE

  Bind scalar variable to REXX variable:
        tie $var, OS2::REXX, "NAME";

  Bind array variable to REXX stem variable:
        tie @var, OS2::REXX, "NAME.";

Only scalar operations work so far. No array assignments, no array operations, ... FORGET IT.

  Bind hash array variable to REXX stem variable:
        tie %var, OS2::REXX, "NAME.";

To access all visible REXX variables via hash array, bind to "";

No array assignments. No array operations, other than hash array operations. Just like the *dbm based implementations.

For the usual REXX stem variables, append a "." to the name, as shown above. If the hash key is part of the stem name, for example if you bind to "", you cannot use lower case in the stem part of the key and it is subject to character set restrictions.

  Erase individual REXX variables (bound or not):
        OS2::REXX::drop("NAME" [, "NAME" [, ...]]);

  Erase REXX variables with given stem (bound or not):
        OS2::REXX::dropall("STEM" [, "STEM" [, ...]]);

  Make Perl functions available in REXX:
        OS2::REXX::register("NAME" [, "NAME" [, ...]]);

Since REXX is not case-sensitive, the names should be uppercase.

Subcommand handlers
By default, the executed REXX code runs without any default subcommand handler present. A subcommand handler named "PERLEVAL" is defined, but not made a default. Use "ADDRESS PERLEVAL" REXX command to make it a default handler; alternatively, use "ADDRESS Handler WhatToDo" to direct a command to the handler you like.

Experiments show that the handler "CMD" is also available; probably it is provided by the REXX runtime.

Interfacing from REXX to Perl
This module provides an interface from Perl to REXX, and from REXX-inside-Perl back to Perl. There is an alternative scenario which allows usage of Perl from inside REXX.

A DLL PerlRexx provides an API to Perl as REXX functions

  PERL
  PERLTERM
  PERLINIT
  PERLEXIT
  PERLEVAL
  PERLLASTERROR
  PERLEXPORTALL
  PERLDROPALL
  PERLDROPALLEXIT

A subcommand handler "PERLEVALSUBCOMMAND" can also be registered. Calling the function PERLEXPORTALL() exports all these functions, as well as exports this subcommand handler under the name "EVALPERL". PERLDROPALL() inverts this action (and unloads PERLEXPORTALL() as well). In particular

  rc = RxFuncAdd("PerlExportAll", 'PerlRexx', "PERLEXPORTALL")
  rc = PerlExportAll()
  res = PERLEVAL(perlarg)
  ADDRESS EVALPERL perlarg1
  rc = PerlDropAllExit()

loads all the functions above, evals the Perl code in the REXX variable "perlarg", putting the result into the REXX variable "res", then evals the Perl code in the REXX variable "perlarg1", and, finally, drops the loaded functions and the subcommand handler, deinitializes the Perl interpreter, and exits the Perl's C runtime library.

PERLEXIT() or PERLDROPALLEXIT() should be called as the last command of the REXX program. (This is considered as a bug.) Their purpose is to flush all the output buffers of the Perl's C runtime library.

"PERLLASTERROR" gives the reason for the failure of the last PERLEVAL(). It is useful inside "signal on syntax" handler. PERLINIT() and PERLTERM() initialize and deinitialize the Perl interpreter.

"PERLEVAL(string)" initializes the Perl interpreter (if needed), and evaluates "string" as Perl code. The result is returned to REXX stringified, undefined result is considered as failure.

"PERL(string)" does the same as "PERLEVAL(string)" wrapped by calls to PERLINIT() and PERLEXIT().

NOTES
Note that while function and variable names are case insensitive in the REXX language, function names exported by a DLL and the REXX variables (as seen by Perl through the chosen API) are all case sensitive!

Most REXX DLLs export function names all upper case, but there are a few which export mixed case names (such as RxExtras). When trying to find the entry point, both exact case and all upper case are searched. If the DLL exports "RxNap", you have to specify the exact case, if it exports "RXOPEN", you can use any case.

To avoid interfering with subroutine names defined by Perl (DESTROY) or used within the REXX module (prefix, find), it is best to use mixed case and to avoid lowercase only or uppercase only names when calling REXX functions. Be consistent. The same function written in different ways results in different Perl stubs.

There is no REXX interpolation on variable names, so the REXX variable name TEST.ONE is not affected by some other REXX variable ONE. And it is not the same variable as TEST.one!

You cannot call REXX functions which are not exported by the DLL. While most DLLs export all their functions, some, like RxFTP, export only "...LoadFuncs", which registers the functions within REXX only.

You cannot call 16-bit DLLs. The few interesting ones I found (FTP,NETB,APPC) do not export their functions.

I do not know whether the REXX API is reentrant with respect to exceptions (signals) when the REXX top-level exception handler is overridden. So unless you know better than I do, do not access REXX variables (probably tied to Perl variables) or call REXX functions which access REXX queues or REXX variables in signal handlers.

See "t/rx*.t" and the next section for examples.

EXAMPLE
  use OS2::REXX;

  sub Ender::DESTROY { $vrexx->VExit; print "Exiting...\n" }

  $vrexx = OS2::REXX->load('VREXX');
  REXX_call {                   # VOpenWindow takes a stem
    local $SIG{TERM} = sub {die}; # enable Ender::DESTROY
    local $SIG{INT} = sub {die};        # enable Ender::DESTROY

    $code = $vrexx->VInit;
    print "Init code = `$code'\n";
    die "error initializing VREXX" if $code eq 'ERROR';

    my $ender = bless [], 'Ender'; # Call Ender::DESTROY on exit

    print "VREXX Version ", $vrexx->VGetVersion, "\n";

    tie %pos, 'OS2::REXX', 'POS.' or die;
    %pos = ( LEFT   => 0, RIGHT  => 7, TOP    => 5, BOTTOM => 0 );

    $id = $vrexx->VOpenWindow('To disconnect:', 'WHITE', 'POS');
    $vrexx->VForeColor($id, 'BLACK');
    $vrexx->VSetFont($id, 'TIME', '30');
    $tlim = time + 60;
    while ( ($r = $tlim - time) >= 0 ) {
      $vrexx->VClearWindow($id);
      $vrexx->VSay($id, 100, 50, (sprintf "%02i:%02i", int($r/60), $r % 60));
      sleep 1;
    }
    print "Close code = `$res'\n" if $res = $vrexx->VCloseWindow($id);
  };

ENVIRONMENT
If "PERL_REXX_DEBUG" is set, prints trace info on calls to REXX runtime environment.

AUTHOR
Andreas Kaiser ak@ananke.s.bawue.de, with additions by Ilya Zakharevich ilya@math.ohio-state.edu.

SEE ALSO
OS2::DLL.