Data-driven code is the solution if you only have the first two requirements. You hard-code a set of rule patterns, then you allow new rules based on the existing patterns. In fact, you would (essentially) have a UI that allowed you to pick the rule, then fill in the blanks. Your datastore, if it's an RDBMS, would have a table for each rule pattern and just go from there.

The moment you have some sort of run-time parsing (required for my third requirement), I would argue that you have run-time introspection. You might not be introspecting the language you are written in, but you are introspecting the language you are parsing. So, yes, your example does run-time introspection over the language of hex numbers. In that sense, string eval is a basis for all forms of run-time introspection in those languages that provide one.

But, I think that's a bit of an easy way out. The question here is the ability to make decisions based on the qualities and attributes of the run-time environment. That's always going to be a set of data structures (in Perl, it's the symbol table). So, you can always view run-time introspection as data-driven programming. The big key, imho, is whether or not the language natively provides facilities for that (such as Perl and Ruby) or forces you to write a DSL that does (like C or Haskell).

My criteria for good software:
  1. Does it work?
  2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?

In reply to Re^5: Runtime introspection: What good is it? by dragonchild
in thread Runtime introspection: What good is it? by BrowserUk

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