src/identity.js

import { Monad } from "./monad";
import { clone } from "./services/clone";
import { equality } from "./services/equality";
import { ErrorM } from "./error";
/**
 * Class Identity - wraps underlying value into the monadic value and compute results from a monadic value.
 * @extends {Monad}
 */
export class Identity extends Monad {
    /**
     * Creates an instance of class Identity.
     * @param {any} [v] - The initial state of app.
     * */
    constructor(v) {
        super();
        /**
         * Keeps underlying value of a monad.
         * @type {any}
         */
        this.v = clone(v);
        /**
         * The instance of ErrorM.
         * @type {ErrorM}
         */
        this.err = new ErrorM();
    }
    /**
     * Chains the operations on a monadic value.
     * @method bind
     * @param {MF<T, U>} f - transformation function for the monad.
     * @param {any} [v = this.v]- underlying value for the monad, it can be null.
     * @return {Pr<U> | Error}
     */
    bind(f, v = this.v) {
        return this.v && v
            ? equality(this.v, v)
                ? f(v)
                : this.fail('Identity.bind() - underlying value of the monad have defined in the constructor!')
            : v || v === 0 || v === '' || v === null
                ? f(v)
                : f();
    }
}
//Copyright (c) 2017 Alex Tranchenko. All rights reserved.