Let's write a compiler, part 4: Testing

[ingve]

https://briancallahan.net/blog/20210817.html

[p4bl0]

For context, there was some discussion here on HN about parts 1 and 3 of this series:

https://news.ycombinator.com/item?id=28183062

https://news.ycombinator.com/item?id=28197876

[rightbyte]

Looking at the code it feels more like an assembler than a compiler since there is no mess and it outputs C code.

But it is very clean and nice. I like the pattern.

[ModernMech → rightbyte]

It seems like we're going to have the same discussion on this topic every day until all parts are posted.

[Joker_vD → rightbyte]

> more like an assembler than a compiler since there is no mess and it outputs C code.

Yes, translating between closely related languages is often like this: the mapping between their constructs is 1-to-1 and almost trivial. But try translating e.g. λ-calculus into C in one go, without separate lambda-lifting/closure-converting steps: it's absolutely doable but quite messy.

[chrisseaton → rightbyte]

> feels more like an assembler than a compiler

Yes it's a kind of transpiler, or template compiler, a typically 1-1 mapping.

[monocasa → rightbyte]

When absolute compiler perf isn't required, I love nanopass compilers for this. Each pass slowly massages a slightly different IR towards the final form and there isn't really a limit to how different the code source and end target can be, just needs more passes.