Formalize grammar

[frostburn]

Replace the parser with a PEG.js AST parser and an AST evaluator.

ref #21

[frostburn]

Tests pass over at scale-workshop too if this branch is used as the dependency.

[frostburn]

Ran this by some scales from the Xenharmonic Alliance Discord. Seems to produce the same results.

[arseniiv]

I see signed integers fractions and comma-decimals should be accepted by the parser; it’s probably hard to check if the whole expression represents something well-defined at parse time but maybe this wasn’t intended.

SW2 doesn’t accept the scale or/and ignores those entries. Even in SW2, -3/2 and -1,5 might have been understood as 2/3 as this additive arithmetic is multiplicative on ratios, but I get why it could’ve been overlooked or intentionally left undefined, as it’s doubly confusing.

[frostburn]

I see signed integers fractions and comma-decimals should be accepted by the parser; it’s probably hard to check if the whole expression represents something well-defined at parse time but maybe this wasn’t intended.

SW2 doesn’t accept the scale or/and ignores those entries. Even in SW2, -3/2 and -1,5 might have been understood as 2/3 as this additive arithmetic is multiplicative on ratios, but I get why it could’ve been overlooked or intentionally left undefined, as it’s doubly confusing.

This is a re-implementation of the existing and poorly laid out grammar of Scale Workshop 2. I regret allowing -3/2 to mean 2/3, but that ship has sailed. I will do better in SW3 if the community allows it.

[arseniiv]

I regret allowing -3/2 to mean 2/3,

But it doesn’t (by itself as a whole row). Then it’s good. But the parser as it is allows it, so transitioning to SW3 parser should catch these places.

[frostburn]

I regret allowing -3/2 to mean 2/3,

But it doesn’t (by itself as a whole row). Then it’s good. But the parser as it is allows it, so transitioning to SW3 parser should catch these places.

That is simply due to a fortunate bug. It was always meant to parse and has been fixed in the latest deployment.

[frostburn]

Self-review: Seems reasonable and should make it easier slot in the new unit system in the next major version.