Pattern for converting procedures to events

[Peter Chen]

I am working on a tutorial explaining how to poeize a procedural
program, in the hope of making it easier for my coworkers to pick up
POE.  

Since I have not worked with POE for that long, I am wondering whether
there is an easier and more elegant way of doing this.  This is what I
have so far, starting with the most basic.  I would appreciate your
feedback.


Given the following function foo: 

  sub foo { 
    &step1() or return (undef, 'step1 failed'); 
    &step2() or return (undef, 'step2 failed'); 
    &step3() or return (undef, 'step3 failed'); 
    &step4(); 
  } 

What's the easiest way to poeize this into the following form: 

  $kernel->post($session, 'foo', $response_postback); 

Assume event foo, step1, ... step4 map to state poe_foo, poe_step1, ...
poe_step4. 

  sub poe_foo { 
    my($kernel, $session, $response) = @_[ KERNEL, SESSION, ARG0 ]; 

    my $postback3 = $session->postback('step4', $response,  $response); 
    my $postback2 = $session->postback('step3', $postback3, $response); 
    my $postback1 = $session->postback('step2', $postback2, $response); 
  
    $kernel->yield('step1', $postback1, $response); 
  } 

  sub poe_step1 { 
    my($kernel, $session, $success_cbk, $failure_cbk) = 
       @_[ KERNEL, SESSION, ARG0, ARG1 ]; 
    my $result = &step1; 
    $result? $success_cbk->($result) : 
      $failure_cbk->(undef, 'step1 failed'); 
  } 
  ... 

Pete