sepBy1 within possibly parses nothing

[devurandom]

Following code (with sepBy1 wrapped as needed to workaround #109):

import {
    optionalWhitespace,
    Parser,
    possibly,
    sepBy1 as _sepBy1,
    sequenceOf,
    str,
    whitespace
} from "arcsecond";

const sepBy1 = <S, T>(sep: Parser<S>, value: Parser<T>) =>
    _sepBy1(sep)(value) as Parser<T[]>;

const b = str("b")
const c = str("c")
const a1 = sequenceOf([
    str("a"),
    possibly(sequenceOf([whitespace, b])),
    possibly(sequenceOf([whitespace, c]))])
const a2 = sequenceOf([
    str("a"),
    possibly(sequenceOf([whitespace, sepBy1(optionalWhitespace, b)])),
    possibly(sequenceOf([whitespace, sepBy1(optionalWhitespace, c)]))])

export const parse1 = (input: string) => a1.run(input);
export const parse2 = (input: string) => a2.run(input);

parses the string "a b c" in the a1 variant, but not in the a2 variant:

❯ pnpm build

> arcsecond-repro3@0.1.0 build [REDACTED]/arcsecond-repro3
> tsc -p .

❯ node
Welcome to Node.js v18.17.1.
Type ".help" for more information.
> p = await import("./dist/parser.js?v1")
[Module: null prototype] {
  parse1: [Function: parse1],
  parse2: [Function: parse2]
}
> p.parse1("a b c")
{
  isError: false,
  result: [ 'a', [ ' ', 'b' ], [ ' ', 'c' ] ],
  index: 5,
  data: null
}
> p.parse2("a b c")
{ isError: false, result: [ 'a', null, null ], index: 1, data: null }

Please find a complete example in https://github.com/devurandom/arcsecond-issue-111-repro.

[devurandom]

I found an implementation of sepBy1 that works:

import {
    coroutine,
    either,
    lookAhead,
    Parser,
    sequenceOf,
} from "arcsecond";

const sepBy1 = <T>(sep: Parser<string>, val: Parser<T>) =>
    coroutine((run) => {
        const results: T[] = [run(val)];

        const next = sequenceOf([sep, val])
        while (!run(either(lookAhead(next))).isError) {
            const [_, value] = run(next);
            results.push(value);
        }

        return results;
    });