As you might (not) have noticed, wenyan-lang strives to be more readable (for ancient Chinese people). Macros provide syntactic sugars to bring the 文采 of your code to the next level.
E.g. Now you can patch wenyan-lang's notorious print function like so:
或云「「書「甲」焉」」。
蓋謂「「吾有一言。曰「甲」。書之」」。
書「「問天地好在」」焉。
Since we're beating JavaScript to macros, here is a rough C equivalence:
#define 書(甲)焉 吾有一言。曰甲。書之
書("問天地好在")焉。See ./examples/macro.wy for detailed usage!
In the 或云 statement, you specify the alternative syntax, using 「甲」,「乙」,「丙」etc. (十天干) to denote arguments, and in the 蓋謂 statement you specify what that statement should be replaced by, referencing the arguments using the same 天干. (more than 10 arguments is considered too hideous and therefore not possible).
It's just like regex.
Macros potentially solve other problems such as using 爲 instead of 為 etc. Currently, stdlib 列經 uses a couple of macros to make Higher-order functions such as map filter and reduce look prettier.
So instead of
施「遍施」於「加一」於「某列」。書之。
you can also do
凡「某列」皆「加一」其上者。書之。
where the syntax is defined by this macro in 列經:
或云「「凡「甲」皆「乙」其上者」」。
蓋謂「「施「遍施」於「乙」於「甲」」」
Your macros cannot start or end with identifier/arguments (e.g. 或云「「書「甲」」」 or 或云「「「甲」焉」」 are BAD. It has to be 或云「「書「甲」焉」」). Otherwise the preprocesser cannot find out where it starts/ends and might not work as expected.
The preprocessing is done before tokenization, and it searches all imported modules and gather all the macros and do the finding and replacing. (It might not be the most efficient way to do it, so if you have a better idea please let me know!). See src/macro.js for details.