🔣 A domain-specific language with handler combinators

[favonia]

1. Dispatching diagnostics to different handlers
2. Duplicating diagnostics to multiple handlers
3. Filtering diagnostics
4. Accumulating diagnostics (?)

[kentookura]

I was going to write a response here that something like a handler combinator thingy is the more natural way to proceed, but you beat me to it :)

[favonia]

@kentookura Are you claiming that with these three combinators you can already implement the features you wanted trivially?

[kentookura]

Yes, I think so

[kentookura]

One thing that I want to point out is that when implementing a language server, it is important that an empty list of diagnostics gets pushed when a computation that previously failed now succeeded. Right now I am checking this manually, but maybe this is an interesting factor when designing this.

Another thing is that diagnostics need a URI to be published to, and a computation might raise diagnostics for many files. I am handling this by

• making sure that all diagnostic loctexts get created with the source argument
• accumulating them in a (Lsp.Uri.t, diagnostic list) Hashtbl.t that gets populated by emit and fatal: I am inspecting the loctext of the diagnostic and creating an Lsp.Uri.t from it.

This is not enough, though:
Say that evaluating file A previously failed and had a diagnostic pushed to it. Running the evaluator again now succeeds, but now I need to know that A failed the last time in order to push an empty list to clear the diagnostics, so I need to track some state.