Thoughts on Bootstrapping GHC (2018) | Hacker News Reader

Thoughts on Bootstrapping GHC (2018)

joachim-breitner.de

60 pointsTomte11 comments

Here is an interesting story from pjmlp about how Wirth bootstrapped Pascal: <https://news.ycombinator.com/item?id=30487264>

I think the only way to go is via an interpreter. That interpreter should be written in C, or some language trivially bootstrapped from C (that rules out C++, unfortunately, which has its own bootstrapping problems).

The interpreter could target a much simpler version of Haskell and it could be slow as hell, as it would be used only once.

Why an interpreter and not a compiler?

Because you only intend to run it once, on one input, and ad-hoc interpreters are usually simpler to write than compilers.

Such a one-off Haskell interpreter might even get away without or with less rigorous type checking.

An interpreter omits the target architecture/format question and thus is more portable than a compiler.

Of course, you could compile to a higher-level language, for instance directly to C. But that's usually still a complication that only gives you performance. And performance is something you probably don't need during bootstrapping.

That is how P-Code was born for Pascal, its original purpose was only to help porting Pascal compilers not to become a widespread target format for environments like UCSD Pascal.

Another point about bootstrapping an ancient version of GHC first and using that to build more modern versions: you need to run the generated x86 code (that also targets an old OS version) to do that, and it’s increasingly not a given that you can do so natively.

wonder could https://www.ioccc.org/2019/lynn/hint.html help here?

This project[0] is a fork of Ben Lynn’s compiler that can be bootstrapped from a binary less than 1 KB in size. The dialect of Haskell it accepts is impressive for its size and GHC-compatible too.

[0] https://github.com/oriansj/blynn-compiler

If you click through the link on that page (and click on Compiler), there are a series of articles on the development process - step by step bootstrapping stages and some further development past that point.

It's a really interesting read:

https://crypto.stanford.edu/~blynn/compiler/

I learned about Mogensen-Scott encoding and some tricks for efficiently compiling to SKI from those articles.

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