Well typing string literals

[ShacharHarshuv]

This suggestion has to do with improving the types, with no functional change.

A lot of string literals in Tonal appear to expect very specific kinds of inputs, but the types show a general string.

For example, the type IntervalName can be improved. Based on the docs, it could be something like this:

type Quality = "dddd" | "ddd" | "dd" | "d" | "m" | "M" | "P" | "A" | "AA" | "AAA" | "AAAA";
type Digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' |'8' | '9';
type Natural = `${Exclude<Digit, '0'>}${Digit | ''}`;
type IntervalName = `${'-' | ''}${Natural}${Quality}`

(Note: I allow only 2 digit numbers but I think that's enough?)

The same thing could be done with chord names, note names, pitch classes, mode names, roman numerals, time durations, time signatures, chord types, scale types etc.

Caveat: some of these entity allow to add custom ones, which means the available types is not known in advance. But with these adding the defaults ones in a union + | string will still at least allow for auto-complete in IDEs, so there is still some value. I think at least for the none extensible ones we shouldn't allow free strings.

I can open a PR for this myself, but first I want to see the opinion of the maintainers of this repository before doing so.

[mrjacobbloom]

I love this idea! The types with a limited set of possible values seem like an easy win.

Some of Tonal's features are extensible in a way that might make it impossible to do this fully (e.x. ChordType.add) But you could explore using a manual list of the most common values and then doing a string suggestion type for everything else.

Be careful making giant combinations of string template types like this, I've seen cases where TypeScript tries to pre-compile all of the combinations and it slows everything down (although this years ago, maybe that's gotten a lot better recently)

You can save yourself a little trouble with the Digit stuff by using number instead, e.x. `${'-' | ''}${number}${Quality}`, although it's more permissive