klister VS mutagen

Yeah, that project is pretty much at the bottom of my list, unfortunately. My top projects these days are mgmt, klister, recursion-schemes, and hint... And that's already too much!

case is a special form, ie a bit of core syntax, but, interestingly, data is not. (It is presumably a macro; typechecking is actually done as a part of macro expansion.) The syntax remains pretty uniform. Or, in Klister, type ascription is done via normal S-expression syntax with a form called the, as (the $type $expression); again, the syntax is uniform.

Shameless plug: we don't have that problem in Klister, because our equivalent to main is a run macro which runs an IO action, and your alternate prelude can define its own run macro which expects an IO action from your alternate prelude.

Klister is very similar to Hackett, but implemented in Haskell instead of Racket, and my most recent PR is from 20 days ago, if that's the metric which counts for you. Still very much of a WIP though.

You might be interested in Klister: https://github.com/gelisam/klister

I've now also found an implementation for klister, which is meant to interleave type checking with macro expansion.

In Klister, which already has Scheme-like macros and Haskell-like types (polymorphism, algebraic types and higher-kinded types, but not yet fancier types like RankNTypes and GADTs), our plan to get the best of both worlds (lexical syntax and typed ASTs) is to separate parsing from macro evaluation. That is, users write their programs using the surface syntax of s-expressions, parsers parse those into typed ASTs, and macros are typed by the type of the ASTs they receive as input and produce as output. At this stage this is only a research idea, I don't know if that's going to work out yet, but I hope so!

There are two testing techniques you didn't mention: Snapshot tests (which are greatly simplified using the insta crate and mutation testing (which can be done on nightly with my mutagen crate.

How does this compare to mutagen?

Do you mean as part of build.rs? Yes, that's certainly doable, and has been done in the past. You can use env!("OUT_DIR") for that. Examples you may want to refer to include my mutagen crate and criterion.

Would be great if this could include mutation testing.

I wrote a good number of macros though, both macro_rules! and various proc_macros. The latest iteration of overflower has both, for example. mutagen is a mutation testing tool built as a proc macro, and it's helper library has a bunch of macros, too. compact_arena uses macros to tie unique lifetime tags to arenas.

Also there are far more mutation testing frameworks. I maintain the rust-based mutagen one. There are also LLVM-based ones (etc. mull) that can cover multiple languages (but may yield mutations not expressible in your preferred one).

Cargo (and Rust) makes it so easy to write test cases that you should really use it to find these kinds of bugs. And there are other good test crates available: mutagen, quickcheck, etc.

I had a student completely reachitecture my mutagen tool, and saw some working on various clippy contributions.