My understanding is that e-graphs take care of selecting the best patch (by examining many options in parallel) but fundamentally it is still copy-and-patch.
Could you elaborate more on "fundamentally it is still copy-and-patch"? From what I can recall when I had first read about copy-and-patch a not-uncommon comparison was against Cranelift, which to me would imply that different approaches were taken. I don't recall any discussion about Cranelift's use of the technique, either, so your claim that it's at the heart of Cranelift is new information to me. Has Cranelift adopted copy-and-patch (maybe for a specific compilation stage?) in the meantime?
There are some experiments in using copy-and-patch for the R language (after Python): https://dl.acm.org/doi/10.1145/3759548.3763370
From a master thesis: https://www.itspy.cz/wp-content/uploads/2025/09/it_spy_2025_...
Related:
Copy-and-Patch: Fast compilation for high-level languages and bytecode (2020) https://news.ycombinator.com/item?id=40553448 - June 2024 (51 comments)
A copy-and-patch JIT compiler for CPython - https://news.ycombinator.com/item?id=38769874 - Dec 2023 (68 comments)
Copy-and-Patch: Fast JIT Compilation for SQL, WebAssembly, and Others - https://news.ycombinator.com/item?id=28547057 - Sept 2021 (7 comments)
the accompanying post "How It Works" is worth reading alongside this tutorial
https://transactional.blog/copy-and-patch/
(key terms: abus[e|ing]: 4, force: 3, trick: 1, chance: 1)
I think this technique also lies at the heart of the Cranelift project.
https://cranelift.dev/
IIRC Cranelift doesn't use copy-and-patch. It uses e-graphs [0] as part of its optimization pipeline, though.
Closest thing in (relatively) recent news that uses copy-and-patch I can think of is CPython's new JIT.
[0]: https://github.com/bytecodealliance/rfcs/pull/27
My understanding is that e-graphs take care of selecting the best patch (by examining many options in parallel) but fundamentally it is still copy-and-patch.
Could you elaborate more on "fundamentally it is still copy-and-patch"? From what I can recall when I had first read about copy-and-patch a not-uncommon comparison was against Cranelift, which to me would imply that different approaches were taken. I don't recall any discussion about Cranelift's use of the technique, either, so your claim that it's at the heart of Cranelift is new information to me. Has Cranelift adopted copy-and-patch (maybe for a specific compilation stage?) in the meantime?
Indeed, the original copy-and-patch paper explicitly compares against Cranelift: https://fredrikbk.com/publications/copy-and-patch.pdf
You are right. Somehow I had in my mind that e-graphs worked with pre-compiled snippets of code but it seems Cranelift does not do that.