parjs/src/internal/combinators/later.ts

Library for building parsers using combinators.

import type { ParsingState } from "../state";

import { Issues } from "../issues";
import type { Parjser } from "../parjser";
import { ParjserBase } from "../parser";

/** A parser with logic to be determined later. Useful for defining some kinds of recursive parsers. */
export interface DelayedParjser<T> extends Parjser<T> {
    init(resolved: Parjser<T>): void;
}

class Late<T> extends ParjserBase<T> implements DelayedParjser<T> {
    type = "later";
    _resolved!: ParjserBase<T>;

    get expecting() {
        return !this._resolved ? "unbound delayed parser" : this._resolved.expecting;
    }

    init(resolved: Parjser<T>) {
        if (this._resolved) Issues.delayedParserAlreadyInit();
        this._resolved = resolved as ParjserBase<T>;
    }

    _apply(ps: ParsingState): void {
        if (!this._resolved) {
            Issues.delayedParserNotInit("");
        }
        this._resolved.apply(ps);
    }
}

/**
 * Returns a parser that has no logic by itself and must be initialized with another parser by
 * calling the parser's `init` function.
 */
export function later<T>(): DelayedParjser<T> {
    return new Late<T>();
}