semantic-source VS hnix

One production example I know: GitHub code navigation is written in Haskell https://github.com/github/semantic

ah, easy. it's because support has not been added into https://github.com/github/semantic which is the tech that powers the GitHub UI. Adding support is pretty easy/mainly glue code [1] that imports the tree sitter API.

[1] https://github.com/github/semantic/blob/793a876ae45d38a6bd17...

GitHub used Haskell for implementing Semantic, a command-line tool for parsing, analyzing, and comparing source code.

As far as engineering effort, you can read this GitHub comment for an overview of where we’d like to take the project in the future. The tl;dr here is that the open sum type view of the world made it very concise to fold over syntax trees (since such a view of data is ultimately unityped, recursion schemes Just Work), but the tradeoff thus associated—namely, that you have to parse a concrete syntax tree into an open-sum view (a complicated and painful-to-read process), that you can never really be sure how a given syntax tree is shaped, and that the types don’t help you nearly as much as they could—proved to be too onerous to deal with. Going forward, we’re generating syntax types from the AST once per target language, and working on an abstraction (probably via this generated code; I made five separate efforts at using Generics for this, and failed every time) that recovers at least some of the convenience of recursion schemes. It turns out that recursion schemes over a mutually recursive syntax tree—as pretty much every language’s syntax trees are, in practice—are pretty much an unsolved problem, especially when extended to languages like TypeScript, which have hundreds of different syntax nodes.

Meanwhile their Tree-Sitter-based semantic parser[1] looks abandoned. There is even rotting for years pull request[2] adding support of the same stack graphs into it.

[1] https://github.com/github/semantic

[2] https://github.com/github/semantic/pull/535

The semantic team at GitHub uses it for statically analyzing the dozens of languages that end up in GitHub repositories: https://github.com/github/semantic/blob/eaf13783838861fe5eb6cd46d59354774a8eb88d/docs/why-haskell.md

Yesterday I was looking for some examples of projects using tree-sitter (which is C) when I found GitHub's semantic, used to analyze and compare source code, and written in Haskell: https://github.com/github/semantic/

I can refere to prelude setup in HNix

I also can nominate HNix: https://github.com/haskell-nix/hnix. Nix is a lazy pure language, HNix is an implementation of Nix in lazy pure language (Haskell). The project was done by a famous expert in the field of compilers/interpreters, which worked on Borland C++ compiler back in a day. The project overall was done by a pretty start team.

Well, maintaining a rewrite of Nix in Haskell: https://github.com/haskell-nix/hnix.

HNix is a Nix (pure lazy language) interpreter/tooling in Haskell. So it is a field&case of pure-to-pure, lazy-to-lazy language creation. HNix is created with fancy design paradigms (design introduction): as recursion schemes (since Nix is a recursive language) & Abstracting Definitional Interpreters. Mentioning these two particularly, as they align HNix to GHC in a natural way, design leverages & projects GHC power to HNix, allowing to concentrate on language implementation.