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by catpolice
2359 days ago
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Last year I decided to write a WASM-targeting compiler in Javascript, completely by hand. The idea was to compile a vaguely C-like toy language to WASM without any external dependencies. Part of the motivation was that while I've written many simple parsers, I mostly used parser generators with BNF grammars and I didn't feel like I had a good sense of how the code I ended up generating actually worked for something with complex syntax and semantics. I felt like I was writing specs for a parser, rather than writing a parser. And I didn't have a huge amount of experience with code generation. My toy language has vaguely C-like syntax with block scope and infix operators with various precedences, so it was a bit more complicated than JSON, but I ended up using something like Pratt parsing/Precedence Climbing (see https://www.oilshell.org/blog/2017/03/31.html) and wrote the whole thing in a way that's - hopefully - pretty easy to read for folks interested in wrapping their head around parsing complex syntax (e.g. with scope and name resolution). The lexer, parser and language definition ended up being about 1000 lines of JS (counting some pretty extensive comments). Code generation is pretty straightforward once you have an AST. Any JS programmers that are interested in really getting into the nitty-gritty of writing your own parser/compiler should check it out. The source is here: https://github.com/j-s-n/WebBS. If you want to play around with the language and inspect the generated ASTs and WASM bytecode, there's an interactive IDE with example code here: https://j-s-n.github.io/WebBS/index.html#splash |
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