Pretty nifty. As of now, the code doesn't compile: there's some stray "span" stuff in codegen.rs[1], and it's trying to format `Warning` which doesn't implement `Display` in main.rs[2].

Fixing these, it runs mostly as advertised, but it seems to assume that one-letter types are always generic parameters, so it's impossible to (for example) generate this:

    struct X;
    enum A {
        P(X),
        Q
    }

Trying this:

    (struct X)
    (enum A (P X) Q)

produces this:

    struct X;
    enum A<P, X> { Q }

while using a multi-letter type like `String`:

    (enum A (P String) Q)

produces the expected:

    enum A { P(String), Q }

One way to solve this would be to always require the generic annotation, and let it be empty when there are no generics, but when I tried that it did something weird:

    (struct X)
    (enum A () (P X) Q)

produces:

    struct X;
    enum A {
        _ /* List([], Some(Span { start: 54, end: 56 })) */,
        P(X),
        Q
    }

I have no idea where the `_` and the comment came from.

[1] https://github.com/ThatXliner/rust-but-lisp/blob/70c51a107b2...

[2] https://github.com/ThatXliner/rust-but-lisp/blob/70c51a107b2...