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# 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.
<details>
<summary>Be careful with the last trick!</summary>
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.
</details>
[specification]: spec/spec.pdf
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