optimization_tips.md

Optimization tips

This document describes a few optimization tips when using Metalang99.

Generally speaking, the fewer reduction steps you perform, the faster you become. A reduction step is a concept defined formally by the specification. Here is its informal (and imprecise) description:

• Every v(...) is a reduction step.
• Every ML99_call(op, ...) induces as many reduction steps as required to evaluate op and ....

To perform fewer reduction steps, you can:

• use ML99_callUneval,
• use plain macros (e.g., ML99_CAT instead of ML99_cat),
• use optimized versions (e.g., ML99_listMapInPlace),
• use tuples/variadics instead of lists,
• call a macro as <X>_IMPL(...), if all the arguments are already evaluated.

Be careful with the last trick!

I strongly recommend to use the last trick only if X is defined locally to a caller so that you can control the correctness of expansion. For example, X can become painted blue, it can emit unexpected commas, the # and ## operators can block expansion of parameters, and a plenty of other nasty things.