Difference between CharIn and Either

[jtrakk]

What is the difference between CharIn and Either? CharIn isn't restricted to Char types, so that might not be the best name, but maybe both CharIn and Either could be OneOf?

[gkappler]

I like your suggested simplification with OneOf but doubt whether eliminating one of the internal implementations is possible without cost -- even though there might be some code-cruft overlap in these types.

The reason is:

• CharIn is optimized for matching the element (Char) at current index in the sequence only (so requires match length 1 that might span multiple codeunits). A internal ismatch function (that can handle case e.g.) is used and state does not keep track of option #.

• Either is very general: iterates through all matches of all options, can match longer subsequences, and retains the matching option # and state.

I agree that CharIn is not a good name when other sequences than Strings are parsed. OneOf is catchy, but suggests a Set like representation, and I find it not matching in cases of a predicate function like CharIn(islowercase). Would ElementIn clean up confusion for you?

[jtrakk]

Would ElementIn clean up confusion for you?

Yeah, though it's a bit weird to say ElementIn('x') since 'x' isn't a container. Single('x') is another option. Or maybe this is a case for Just.

[gkappler]

With Just I think of Maybe Nothing ;-).

You could say parser('x') in your example.

ElementIn('x', 'y'), ElementIn("xy") make sense, yes?

Doe ValueIn('x', 'y'), ValueIn("xy") make more sense to you?

Another alternative would be to decide what implementation is used in the Either constructor?