Stream: ideas

Topic: ignore fields in record builders

Agus Zubiaga (Jun 22 2024 at 21:51):

As part of rewriting record builders, I'd like to make it possible to have bits that are included in the chain, but whose values are ignored.

I think would be particularly helpful for parser combinators:

Parser.combine <- {
    year: Parser.int,
    _: Parser.symbol "/",
    month: Parser.int,
    _: Parser.symbol "/",
    day: Parser.int,
}

However, it'd also be useful for Task when you only care about the result of some in the batch.

Brendan Hansknecht (Jun 23 2024 at 04:22):

So the _ would not record a value, but would still be able to lead to a failure that is recorded by the combined parser?

Agus Zubiaga (Jun 23 2024 at 05:04):

Yeah, Parser.symbol "/" would still be chained with Parser.combine like the rest, but the value it produces would be ignored and won’t appear in the record

Agus Zubiaga (Jun 23 2024 at 05:07):

So it produces the effect and failures can propagate, we just don’t care about the result ok value

Brendan Hansknecht (Jun 23 2024 at 05:22):

Sounds awesome

Last updated: Jun 16 2026 at 16:19 UTC