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Comment by enriquto | Hacker News Reader

What is this sorcery?

    #include <datatype99.h>
    
    datatype(
            BinaryTree,
            (Leaf, int),
            (Node, struct BinaryTree *, int, struct BinaryTree *)
    );

What kind of preprocessor black magic can you do so that this code compiles? I don't dare to open the file datatype99.h lest it casts a dark spell on me.

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Yes, as others have already noticed, it is implemented on top of https://github.com/Hirrolot/epilepsy, a metalanguage for preprocessor metaprogramming.

> a metalanguage for preprocessor metaprogramming

That sentence is everything I was taught to avoid. Props to you.

I like the drug/alcohol metaphor for these things, as a child avoid them, as an adult do your thing as long as you remain sensible.

Funny you use this example, the author's GH page says he's 16; in many countries he wouldn't be able to drink, event responsibly ^^

> in many countries he wouldn't be able to drink

But in most countries they would be able to drink (especially in a private setting), just not purchase. In Europe for instance less than half a dozen countries have a minimum drinking age for private settings, and a dozen more have an MDA in public (but not private), though for some 16 is enough to drink fermented alcohols (alongside a meal with adults for the UK, regardless for Germany and Austria).

LOL, I cannot get enough of this shit! Can you point to some cool implementation tricks that you used to achieve that? I guess there's quite a bit of ## concatenation to create temporary names and stuff?

Well, mostly I use idioms from the Cloak Wiki (https://github.com/pfultz2/Cloak/wiki/C-Preprocessor-tricks,...). It takes some time to realise them :)

In case anybody mistakenly thinks doing so is 'cheating', you're the author of both libraries!

This is absurd, but in a good way.

The whole system seems to be built on top of variadic macros (which had been standardized in C99).

https://github.com/Hirrolot/epilepsy

According to the GitHub, which appears to be a metaprogramming library by the same author.

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