Does choice guarantee order?

[baanan]

In the documentation for or, it says

If both parsers succeed, the output of the first parser is guaranteed to be prioritized over the output of the second.

Does this also hold true for choice?

[zesterer]

Yes, this also holds for choice. Chumsky is a PEG parser, so ambiguity is resolved by simply using the order of patterns as the tie-breaking mechanism.

As mentioned in the docs, choice has a few tradeoff compared to or chains:

• It's significantly faster to compile (I'm hoping that a future version of Rust will be able to memoise trait solving to fix this)
• Its error selection is very slightly weaker (but still sufficient for 90% of use-cases)

[baanan]

ok, thanks