parjs/src/internal/combinators/must.ts

A parser-combinator library for JavaScript.

/**
 * @module parjs/combinators
 */
/** */

import {ParsingState} from "../state";
import {FailureInfo} from "../result";
import {ParjsValidator} from "../parjser";
import {ParjsCombinator} from "../../";
import {defineCombinator} from "./combinator";
import {ParjserBase} from "../parser";
import defaults from "lodash/defaults";


/**
 * Applies the source parser and makes sure its result fulfills `predicate`.
 * @param predicate The condition to check for.
 */
export function must<T>(predicate: ParjsValidator<T>)
    : ParjsCombinator<T, T> {
    return defineCombinator(source => {
        return new class Must extends ParjserBase {
            type = "must";
            expecting = `internal parser ${source.type} yielding a result satisfying condition`;

            _apply(ps: ParsingState): void {
                source.apply(ps);
                if (!ps.isOk) {
                    return;
                }
                let result = predicate(ps.value, ps.userState);
                if (result === true) return;
                ps.kind = result.kind || "Soft";
                ps.reason = result.reason || "failed to fulfill a predicate";
            }

        }();
    });
}