I just realized it breaks on Functions Argument Types which contain parenthesis since gleamType is not aware of them.
Ill convert this PR to a draft and take a look tomorrow.

okay I tried now for some time. I can't figure out how to make nested types work.
I managed to get simple types like List(String) to work but only because I hardcoded the first recursion of gleamType (change not commited).
I don't really have the skills to make this work for infinite nested types.

This also looked a little odd because parenthesis got highlighted as well.

The main issue is that the gleamFunctionArguments is a region which starts with ( and ends with ). The parenthesis in the argument type break this region.

@lpil do you have any idea on how to make this work?

@lpil do you have any idea on how to make this work?

I do not I'm afraid :(

I will close this pr for now and just keep the issue around. Maybe someone with the right skills finds the time to work on it. I think for advanced features like this the whole syntax definition would need a rewrite.