[celeritascelery]

I tried doing something similar to this once. I ran into an issue where I couldn’t define symbols with a dash in them (DEFINE MY-FN…). This is because rust will split the tokens on a dash. It was a small thing, but it meant I couldn’t just copy and paste snippets from a real lisp, I had to transform everything to underscore. Is it the same in your implementation?

[quasigloam]

Yes, at the moment I just assume that all atoms are rust idents because that makes it easier to implement (I can just match against $x:ident), so it doesn't support dashes in atoms. I guess you could match against `$x:ident $(- $y:ident)*` instead? That should work I think, I'd have to change some details in some of the arms but it seems like that would be possible.

[throwup238]

Wouldn’t that match “(foo - bar)” as well as “(foo-bar)”? I don’t think you can get around token whitespace in macro_rules

[quasigloam]

Yes it would match both, this would require us to assume that "foo - bar" can only be an atom. It's not a great solution.

[celeritascelery]

It would, but lisp has prefix operators, so you wouldn’t have to worry about it getting confused.

[quasigloam]

Although in a Lisp such as Scheme, you could pass around the negation operator in something like (map - '(1 2 3)), so it would be a valid concern that it might clash.

[tmtvl]

The problem with that is that there are spaces between map, -, and '(1 2 3). The only way to get spaces into a name is by using vertical bars:

  (defvar |do i 10| 1.100)

[anothername12]

Does Rust have something like a reader macro where you can have arbitrary syntax for a bit?

[throwup238]

It's almost but not quite arbitrary. It still has to be a valid Rust token stream with matching braces/parens. Since it's whitespace insensitive with respect to tokens and "-" is its own token, "(foo-bar)" and "(foo - bar)" result in the same token stream minus the span information.

You can use proc_macro::Span.line()/column() [1] to track how much whitespace there is between tokens and merge them, but the macro will have to rename them to valid Rust identities ("foo-bar" to "foo_bar") and make sure there's no collisions.

[1] https://doc.rust-lang.org/proc_macro/struct.Span.html#method...

[zozbot234]

> I ran into an issue where I couldn’t define symbols with a dash in them

I'm not seeing any issue? (DEFINE MYᜭFN...) works just fine.