Pikt Rule Sections

[posted 2002/03/14]

[The following is the gist of a message sent to another contributor.]

In looking at your script, I noticed that you group all of the =postfix_checkfor()'s under a single rule.  I would instead have each =postfix_checkfor() in its own separate rule.

The idea behind Pikt rule sections is to group together code to check for one thing.  It seems to me that you are checking for five different things here, hence my thinking there should be five separate rules.

I would have done something like this

    rule    // Check for attachments
            =postfix_checkfor(...)

    rule    // Check for unknown recipients
            =postfix_checkfor(...)

    rule    // Check for relay attempts
            =postfix_checkfor(...)

    ...

The PIKT Reference has this to say about rules:

  The input processing loop comprises one or more rule sections.  Strictly
  speaking, there is never a need to break up the set of input processing
  statements into separate rule sections, but doing so helps clarify
  program logic.  (A rule line is also a handy place to put comments.)  A
  rule section, then, usually groups together program statements pertaining
  to a single thing, just one attribute of the current input line. 

There are several other non-trivial benefits to employing multiple rule sections (more than the required single rule).  You have a few additional flow control statements to play around with, including

        again                  repeat the current rule
        leave                  leave the current rule and go on to the next

not to mention

        skip n                 skip ahead n input lines, and resume with
                               the first rule

Also, pikt-1.16.0pre2 introduces the new #rule() (aka #rulenumber()) function.  See the item at the PIKT NEWS web page for #rule()'s use as a debugging aid.

I think that employing multiple rules versus just a single rule is more than a mere stylistic question (akin to debates about what's the best brace-and- indent style in Perl or C).  Using Pikt rule sections and multiple rules intelligently can have important benefits, most especially for script intelligibility (also for encouraging code comments).

The script as you wrote it is pretty clear enough. I'm only trying to point out a nuance you may have missed.

For more examples, see Developer's Notes.