Please create a system that fulfills all of the following requirements:
  1. The system must make decisions based on a series of rules.
  2. These rules must be changeable on the fly.
  3. The set of acceptable rule formats must be changeable on the fly. In other words, a new type of rule must be addable during run-time.
This is not an academic exercise - it's the very essence of a trading system. It also happens to be a subset of the requirements for Prolog (and similar languages).

Implementing #1 is easily done with a set of if-statements if you can assume a set of rules known at compile-time. Implementing #2 is easily done with a data-driven set of functions if you can assume a set of rule formats known at compile-time. #3 is the sticky wicket.

If you allow for run-time introspection, then you can easily build this using function factories. I would be very interested in hearing a solution that is not implemented on top of some form of run-time introspection. These systems tend to be written in a language that provides run-time introspection (either to the programmer or to the compiler). If they aren't, then the programmers tend to write an interpreter which, within it, provides run-time introspection. I haven't heard of a system that meets all three requirements and doesn't use run-time introspection as a key piece to solve the problem.

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: Runtime introspection: What good is it? by dragonchild
in thread Runtime introspection: What good is it? by BrowserUk

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