@yagni-js/yagni/dist/yagni.cjs.js

Yet another functional library

/**
 *
 * @module @yagni-js/yagni
 * @version 0.7.1
 * @author Yuri Egorov <ysegorov at gmail dot com>
 * @license Unlicense http://unlicense.org
 *
 */

'use strict';

Object.defineProperty(exports, '__esModule', { value: true });

/**
 * Takes three functions `predicate`, `fnIf` and `fnElse` as an arguments
 * and returns **a new function**, which then takes `smth` as an argument
 * and returns **the result of calling either `fnIf` or `fnElse`** function
 * depending on the result of calling `predicate` function.
 *
 * @category Logic
 *
 * @param {Function} predicate function to check a condition
 * @param {Function} fnIf function to call if `predicate` evaluates to true
 * @param {Function} fnElse function to call if `predicate` evaluates to false
 * @returns {Function} a new function to take `smth` as an argument and return
 * the result of calling either `fnIf(smth)` or `fnElse(smth)` function
 * depending on the `predicate(smth)` call result
 *
 * @example
 *
 *     import {ifElse} from '@yagni-js/yagni';
 *
 *     function isNil(smth) { return smth === void 0 || smth === null; }
 *     function ifDefined(smth) { return smth; }
 *     function ifUndefined(smth) { return 'foo'; }
 *
 *     const valueOrFoo = ifElse(isNil, ifUndefined, ifDefined);
 *
 *     const res0 = valueOrFoo(null);   // => 'foo'
 *     const res1 = valueOrFoo('baz');  // => 'baz'
 *     const res2 = valueOrFoo('bar');  // => 'bar'
 *
 *     // same thing using only `@yagni-js/yagni` functions
 *
 *     import {isNil, identity, always, ifElse} from '@yagni-js/yagni';
 *
 *     const valueOrFoo = ifElse(isNil, always('foo'), identity);
 *
 *     const res0 = valueOrFoo(null);   // => 'foo'
 *     const res1 = valueOrFoo('baz');  // => 'baz'
 *     const res2 = valueOrFoo('bar');  // => 'bar'
 *
 */
function ifElse(predicate, fnIf, fnElse) {
  return function _ifElse(smth) {
    return predicate(smth) ? fnIf(smth) : fnElse(smth);
  };
}


/**
 * Takes two functions `left` and `right` as arguments and returns
 * **a new function**, which then takes some value `smth` as an argument
 * and returns **boolean** - `true` if both `left(smth)` and `right(smth)`
 * calls return true and `false` otherwise
 *
 * @category Logic
 *
 * @param {Function} left predicate function to calculate left side value
 * @param {Function} right predicate function to calculate right side value
 * @returns {Function} a new function to take `smth` as an argument and
 * return true if both `left(smth)` and `right(smth)` evaluate to true and
 * false otherwise
 *
 * @example
 *
 *     import {and} from '@yagni-js/yagni';
 *
 *     function above0(smth) { return smth > 0; }
 *     function below100(smth) { return smth < 100; }
 *
 *     const test = and(above0, below100);
 *
 *     const res0 = test(42);   // => true
 *     const res1 = test(-1);   // => false
 *     const res2 = test(101);  // => false
 *
 */
function and(left, right) {
  return function _and(smth) {
    return left(smth) && right(smth);
  };
}


/**
 * Takes two functions `left` and `right` as arguments and returns
 * **a new function**, which then takes some value `smth` as an argument
 * and returns **boolean** - `true` if `left(smth)` or `right(smth)`
 * calls return true and `false` otherwise
 *
 * @category Logic
 *
 * @param {Function} left predicate function to calculate left side value
 * @param {Function} right predicate function to calculate right side value
 * @returns {Function} a new function to take `smth` as an argument and
 * return true if `left(smth)` or `right(smth)` evaluates to true and
 * false otherwise
 *
 * @example
 *
 *     import {or} from '@yagni-js/yagni';
 *
 *     function below0(smth) { return smth < 0; }
 *     function above100(smth) { return smth > 100; }
 *
 *     const test = or(below0, above100);
 *
 *     const res0 = test(42);   // => false
 *     const res1 = test(-1);   // => true
 *     const res2 = test(101);  // => true
 *
 */
function or(left, right) {
  return function _or(smth) {
    return left(smth) || right(smth);
  };
}


/**
 * Takes a function `test` and returns **a new function**, which then
 * takes some value `smth` as an argument and returns **negated result** of the
 * call `test(smth)`.
 *
 * @category Logic
 *
 * @param {Function} test predicate function
 * @returns {Function} a new function to take `smth` as an argument and return
 * `!` of the call `test(smth)`
 *
 * @example
 *
 *     import {not} from '@yagni-js/yagni';
 *
 *     function equalsFoo(smth) { return smth === 'foo'; }
 *
 *     const notEqualsFoo = not(equalsFoo);
 *
 *     const res0 = notEqualsFoo('foo');  // => false
 *     const res1 = notEqualsFoo('baz');  // => true
 *     const res2 = notEqualsFoo('bar');  // => true
 *
 */
function not(test) {
  return function _not(smth) {
    return !test(smth);
  };
}

/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is `null` or `undefined`, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is `null` or `undefined`, `false` otherwise
 *
 * @example
 *
 *     import {isNil} from '@yagni-js/yagni';
 *
 *     var a;
 *
 *     const res0 = isNil(null);   // => true
 *     const res1 = isNil(a);      // => true
 *     const res2 = isNil('foo');  // => false
 *     const res3 = isNil(42);     // => false
 *     const res4 = isNil({});     // => false
 *     const res5 = isNil([]);     // => false
 *
 */
function isNil(smth) {
  return (smth === null) || (smth === void 0);
}


/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is not `null` and not `undefined`, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is not `null` and not `undefined`,
 * `false` otherwise
 *
 * @example
 *
 *     import {isDefined} from '@yagni-js/yagni';
 *
 *     var a;
 *
 *     const res0 = isDefined(null);   // => false
 *     const res1 = isDefined(a);      // => false
 *     const res2 = isDefined('foo');  // => true
 *     const res3 = isDefined(42);     // => true
 *     const res4 = isDefined({});     // => true
 *     const res5 = isDefined([]);     // => true
 *
 */
function isDefined(smth) {
  return !isNil(smth);
}


/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is an array, `false` otherwise.
 *
 * Delegates to `Array.isArray` method.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is an array, false otherwise
 *
 * @example
 *
 *     import {isArray} from '@yagni-js/yagni';
 *
 *     const res0 = isArray([]);   // => true
 *     const res1 = isArray({});   // => false
 *     const res2 = isArray(42);   // => false
 *
 */
function isArray(smth) {
  return Array.isArray(smth);
}


/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is an instance of Object, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is an instance of Object, false otherwise
 *
 * @example
 *
 *     import {isObject} from '@yagni-js/yagni';
 *
 *     const res0 = isObject({});   // => true
 *     const res1 = isObject([]);   // => false
 *     const res2 = isObject(42);   // => false
 *
 */
function isObject(smth) {
  return Object.prototype.toString.call(smth) === '[object Object]';
}


/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is a string, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is a string, false otherwise
 *
 * @example
 *
 *     import {isString} from '@yagni-js/yagni';
 *
 *     const res0 = isString('foo');   // => true
 *     const res1 = isString([]);      // => false
 *     const res2 = isString(42);      // => false
 *
 */
function isString(smth) {
  return Object.prototype.toString.call(smth) === '[object String]';
}


/**
 * Takes some value `smth` as an argument and returns **boolean** -
 * `true` if `smth` is a function, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` is a function, false otherwise
 *
 * @example
 *
 *     import {isFunction} from '@yagni-js/yagni';
 *
 *     function foo() { return 'baz'; }
 *
 *     const res0 = isFunction(foo);   // => true
 *     const res1 = isFunction([]);    // => false
 *     const res2 = isFunction(42);    // => false
 *
 */
function isFunction(smth) {
  return Object.prototype.toString.call(smth) === '[object Function]';
}


/**
 * Takes some value `smth` as an argument and returns **boolean**
 * `true` if `smth` strictly equals to `true`, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` strictly equals to `true`, false otherwise
 *
 * @example
 *
 *     import {isTrue} from '@yagni-js/yagni';
 *
 *     const foo = true;
 *     const baz = 42;
 *     const bar = false;
 *
 *     const res0 = isTrue(foo);   // => true
 *     const res1 = isTrue(baz);   // => false
 *     const res2 = isTrue(bar);   // => false
 *
 */
function isTrue(smth) {
  return smth === true;
}


/**
 * Takes some value `smth` as an argument and returns **boolean**
 * `true` if `smth` strictly equals to `false`, `false` otherwise.
 *
 * @category Test
 *
 * @param {*} smth value to test
 * @returns {Boolean} true if `smth` strictly equals to `false`, false otherwise
 *
 * @example
 *
 *     import {isFalse} from '@yagni-js/yagni';
 *
 *     const foo = false;
 *     const baz = 42;
 *     const bar = true;
 *
 *     const res0 = isFalse(foo);   // => true
 *     const res1 = isFalse(baz);   // => false
 *     const res2 = isFalse(bar);   // => false
 *
 */
function isFalse(smth) {
  return smth === false;
}


/**
 * Takes some value `left` as an argument and returns **a new function**,
 * which then takes some value `right` as an argument and returns **boolean**
 * as a result of strict comparision of `left` and `right`.
 *
 * @category Test
 *
 * @param {*} left some value to check equality to
 * @returns {Function} a new function to take `right` as an argument and
 * return true if `left` is strictly equal to `right` or false otherwise
 *
 * @example
 *
 *     import {equals} from '@yagni-js/yagni';
 *
 *     const isZero = equals(0);
 *
 *     const res0 = isZero(0);   // => true
 *     const res1 = isZero(42);  // => false
 *
 */
function equals(left) {
  return function _equals(right) {
    return left === right;
  };
}

/**
 * Takes a function `sideEffect` as an argument and returns **a new function**,
 * which then takes some value `smth` as an argument, calls `sideEffect(smth)`
 * throwing away it's result and returns back **`smth`**.
 *
 * @category Impure
 *
 * @param {Function} sideEffect function to call
 * @returns {Function} a new function to take `smth` as an argument, perform
 * a call `sideEffect(smth)` throwing away it's result and return `smth`
 *
 * @example
 *
 *     import {tap} from '@yagni-js/yagni';
 *
 *     const log = tap(console.log);
 *
 *     const res0 = log('foo');  // => 'foo', logs to console 'foo'
 *     const res1 = log(42);     // => 42, logs to console 42
 *
 */
function tap(sideEffect) {
  return function (smth) {
    // NB. side effect
    // eslint-disable-next-line fp/no-unused-expression
    const r = sideEffect(smth);
    return smth;
  };
}


/**
 * Takes object, attribute name and new value for the attribute as arguments,
 * performs mutation and returns same object.
 *
 * @category Impure
 *
 * @param {Object} subj object to mutate
 * @param {String} attr attribute name
 * @param {*} value new value to assign to the attribute
 * @returns {Object} source object `subj`
 *
 * @example
 *
 *     import {mutate} from '@yagni-js/yagni';
 *
 *     var a = {};
 *
 *     var b = mutate(a, 'foo', 'baz');  // => {foo: 'baz'}, a === b
 *     var c = mutate(b, 'bar', 42);     // => {foo: 'baz', bar: 42}, b === c
 *
 */
function mutate(subj, attr, value) {
  // eslint-disable-next-line fp/no-mutation
  subj[attr] = value;
  return subj;
}

/**
 * Takes `key` and `value` as arguments and returns **a new object**.
 *
 * Uses `mutate` to mutate newly created empty object.
 *
 * @category Object
 *
 * @param {String} key key name
 * @param {*} value key value
 * @returns {Object} a new object, which has only one key
 *
 * @see mutate
 *
 * @example
 *
 *     import {obj} from '@yagni-js/yagni';
 *
 *     const o1 = obj('foo', 'baz');  // => {foo: 'baz'}
 *     const o2 = obj({'bar', 42);    // => {bar: 42}
 *
 */
function obj(key, value) {
  return mutate({}, key, value);
}


/**
 * Takes `key` as an argument and returns **a new function**, which then takes
 * some `value` as an argument and returns **a new object**.
 *
 * @category Object
 *
 * @param {String} key key name
 * @returns {Function} a new function to take `value` as an argument and return
 * a new object
 *
 * @see obj
 *
 * @example
 *
 *     import {objOf} from '@yagni-js/yagni';
 *
 *     const fooObj = objOf('foo');
 *
 *     const o1 = fooObj('baz');  // => {foo: 'baz'}
 *     const o2 = fooObj('bar');  // => {foo: 'bar'}
 *     const o3 = fooObj(42);     // => {foo: 42}
 *
 */
function objOf(key) {
  return function (value) {
    return obj(key, value);
  };
}


/**
 * Takes an object `a` as an argument and returns **a new function**,
 * which then takes an object `b` as an argument and returns **a new object**
 * as a result of merging `a` and `b`.
 *
 * Uses `Object.assign` method. Keeps source objects `a` and `b` untouched.
 *
 * @category Object
 *
 * @param {Object} a
 * @returns {Function} a new function to take an object `b` as an argument
 * and return a new object as a result of merging `a` and `b`
 *
 * @example
 *
 *     import {merge} from '@yagni-js/yagni';
 *
 *     const a = {foo: 'baz'};
 *     const b = {bar: 42};
 *     const mergeA = merge(a);
 *
 *     const res = mergeA(b);
 *     // => {foo: 'baz', bar: 42}, res !== a, res !== b
 *
 */
function merge(a) {
  return function (b) {
    return Object.assign({}, a, b);
  };
}


/**
 * Takes `key` name as an argument and returns **a new function**, which then
 * takes some object `smth` as an argument and returns **value** taken from
 * `smth` by `key`.
 *
 * @category Object
 *
 * @param {String} key key name
 * @returns {Function} a new function to take `smth` as an argument and
 * return value taken from `smth` by `key`
 *
 * @see pickFrom
 * @see pickPath
 *
 * @example
 *
 *     import {pick} from '@yagni-js/yagni';
 *
 *     const src = {foo: 12, baz: 42, bar: 80};
 *     const pickFoo = pick('foo');
 *     const pickBaz = pick('baz');
 *     const pickBar = pick('bar');
 *
 *     const foo = pickFoo(src);  // => 12
 *     const baz = pickBaz(src);  // => 42
 *     const bar = pickBar(src);  // => 80
 *
 */
function pick(key) {
  return function (smth) {
    return smth[key];
  };
}


/**
 * Takes some object `smth` as an argument and returns **a new function**,
 * which then takes `key` name as an argument and returns **value** taken from
 * `smth` by `key`.
 *
 * @category Object
 *
 * @param {Object} smth source object
 * @returns {Function} a new function to take `key` name as an argument and
 * return value taken from `smth` by `key`
 *
 * @see pick
 * @see pickPath
 *
 * @example
 *
 *     import {pickFrom} from '@yagni-js/yagni';
 *
 *     const src = {foo: 12, baz: 42, bar: 80};
 *     const pickSrc = pickFrom(src);
 *
 *     const foo = pickSrc('foo');  // => 12
 *     const baz = pickSrc('baz');  // => 42
 *     const bar = pickSrc('bar');  // => 80
 *
 */
function pickFrom(smth) {
  return function (key) {
    return smth[key];
  };
}


/**
 * Takes an array of key names chain `arr` as an argument and returns
 * **a new function**, which then takes an object `smth` and returns
 * **last value** in chain of keys from `arr` or `undefined`.
 *
 * Uses `reduce` method of `arr` argument.
 *
 * @category Object
 *
 * @param {Array} arr array of key names
 * @returns {Function} a new function to take some object `smth`
 * as an argument and return last value in chain of keys from `arr` or
 * `undefined`
 *
 * @see pick
 * @see pickFrom
 *
 * @example
 *
 *     import {pickPath} from '@yagni-js/yagni';
 *
 *     const path = ['foo', 'baz', 'bar'];
 *     const getFooBazBar = pickPath(path);
 *
 *     const src = {
 *       foo: {
 *         baz: {
 *           bar: 42
 *         }
 *       }
 *     };
 *
 *     const res0 = getFooBazBar(src);        // => 42
 *     const res1 = getFooBazBar({foo: {}});  // => undefined
 *     const res2 = getFooBazBar({});         // => undefined
 */
function pickPath(arr) {
  return function (smth) {
    return arr.reduce(function (acc, key) { return isNil(acc) ? acc : acc[key]; }, smth);
  };
}


/**
 * Takes key name `key` as an argument and returns **a new function**,
 * which then takes some object `smth` as an argument and returns
 * **boolean** - `true` in case object has defined value for `key`,
 * `false` otherwise.
 *
 * @category Object
 *
 * @param {String} key key name
 * @returns {Function} a new function to take some object `smth` as an argument
 * and return true if `smth` has defined value for `key`, `false` otherwise
 *
 * @example
 *
 *     import {has} from '@yagni-js/yagni';
 *
 *     const hasFoo = has('foo');
 *     const hasBaz = has('baz');
 *
 *     const src = {foo: 42};
 *
 *     const res0 = hasFoo(src);  // => true
 *     const res1 = hasBaz(src);  // => false
 *
 */
function has(key) {
  return function (smth) {
    return isDefined(smth[key]);
  };
}


/**
 * Takes some object `smth` and returns **an array** of key names.
 *
 * Uses `Object.keys` to get the result.
 *
 * @category Object
 *
 * @param {Object} smth source object
 * @returns {Array} an array of key names
 *
 * @see values
 * @see items
 *
 * @example
 *
 *     import {keys} from '@yagni-js/yagni';
 *
 *     const res = keys({foo: 42, baz: 'bar'});  // => ['foo', 'baz'];
 *
 */
function keys(smth) {
  return Object.keys(smth);
}


/**
 * Takes some object `smth` and returns **an array** of values.
 *
 * @category Object
 *
 * @param {Object} smth source object
 * @returns {Array} an array of values
 *
 * @see keys
 * @see items
 *
 * @example
 *
 *     import {values} from '@yagni-js/yagni';
 *
 *     const res = values({foo: 42, baz: 'bar'});  // => [42, 'bar'];
 *
 */
function values(smth) {
  return keys(smth).map(function (key) { return smth[key]; });
}


/**
 * Takes some object `smth` as an argument and returns **an array** of objects,
 * each object has correspondent `key` and `value` fields taken from `smth`.
 *
 * @category Object
 *
 * @param {Object} smth source object
 * @returns {Array} an array of objects
 *
 * @see keys
 * @see values
 *
 * @example
 *
 *     import {items} from '@yagni-js/yagni';
 *
 *     const src = {foo: 42, baz: 'bar'};
 *
 *     const res = items(src);
 *     // =>
 *     // [
 *     //   {key: 'foo', value: 42},
 *     //   {key: 'baz', value: 'bar'}
 *     // ]
 *
 */
function items(smth) {
  return keys(smth).map(function (key) { return {key: key, value: smth[key]}; });
}


/**
 * Takes an array of key names `arr` and returns **a new function**,
 * which then takes some object `smth` and returns **a new object**, which
 * doesn't have specified in `arr` keys.
 *
 * @category Object
 *
 * @param {Array} arr an array of key names to exclude
 * @returns {Function} a new function to take some object `smth`
 * as an argument and return a new object with keys from `arr` excluded
 *
 * @example
 *
 *     import {omit} from '@yagni-js/yagni';
 *
 *     const src = {foo: 'foo', baz: 'baz', bar: 'bar'};
 *     const omitFoo = omit(['foo']);
 *     const omitBazBar = omit(['baz', 'bar']);
 *
 *     const res0 = omitFoo(src);     // => {baz: 'baz', bar: 'bar'}
 *     const res1 = omitBazBar(src);  // => {foo: 'foo'}
 *
 */
function omit(arr) {
  return function _omit(smth) {
    return keys(smth).reduce(
      function (acc, key) {
        return arr.indexOf(key) === -1 ? Object.assign({}, acc, obj(key, smth[key])) : acc;
      },
      {}
    );
  };
}


/**
 * Takes a function `mapper` as an argument and returns **a new function**,
 * which then takes an object `obj` as an argument and returns **a new array**,
 * produced by applying `mapper` to each `(key, value)` pair of `obj`.
 *
 * `mapper` function must have the following signature:
 *
 *     function mapper(key, value[, idx])
 *
 * Delegates to `map` method of array of `obj` keys.
 *
 * @category Object
 *
 * @param {Function} mapper function to apply to each `(key, value)` pair
 * of source object
 * @returns {Function} a new function to take an object `obj` as an argument
 * and produce a new array by applying `mapper` to each `(key, value)` pair
 * of `obj`.
 *
 * @see map
 *
 * @example
 *     import {mapObj} from '@yagni-js/yagni';
 *
 *     function toParam(key, value) { return key + '=' + value; }
 *     const mapper = mapObj(toParam);
 *
 *     const src = {foo: 'baz', bar: 42};
 *
 *     const res = mapper(src);  // => ['foo=baz', 'bar=42']
 *
 */
function mapObj(mapper) {
  return function _mapObj(obj) {
    return keys(obj).map(
      function __mapObj(key, idx) {
        return mapper(key, obj[key], idx);
      }
    );
  };
}


/**
 * Takes a function `reducer` as an argument and returns **a new function**,
 * which then takes an object `obj` as an argument and returns
 * **a new function**, which then takes some `initial` value as an argument
 * resulting **in a single output value**, produced by executing the specified
 * `reducer` function on each `(key, value)` pair from `obj`.
 *
 * `reducer` function must have the following signature:
 *
 *     function reducer(accumulator, key, value[, idx])
 *
 * and must return single output value.
 *
 * Delegates to `reduce` method of array of `obj` keys.
 *
 * @category Object
 *
 * @param {Function} reducer function to iteratively apply to each key, value
 * pair of source object
 * @returns {Function} a new function to take `obj` as an argument and
 * produce another new function to take `initial` value and execute
 * `reducer` function over each `(key, value)` pair of the `obj`
 * producing a single output value
 *
 * @see reduce
 *
 * @example
 *     import {reduceObj} from '@yagni-js/yagni';
 *
 *     function swap(acc, key, value) {
 *       return Object.assign({}, acc, _.obj(value, key));
 *     }
 *     const swapper = reduceObj(swap);
 *     const data = {foo: 'baz', bar: 42};
 *     const swapData = swapper(data);
 *
 *     const res0 = swapData({});
 *     // =>
 *     // {baz: 'foo', '42': 'bar'}
 *
 *     const res1 = swapData({lorem: 'ipsum'});
 *     // =>
 *     // {baz: 'foo', '42': 'bar', ipsum: 'lorem'}
 *
 */
function reduceObj(reducer) {
  return function _reduceObj(obj) {
    return function __reduceObj(initial) {
      return keys(obj).reduce(
        function ___reduceObj(acc, key, idx) {
          return reducer(acc, key, obj[key], idx);
        },
        initial
      );
    };
  };
}

/**
 * Takes an array-like object `smth` as input
 * and returns **a new array**.
 *
 * Delegates to `Array.prototype.slice` method call.
 *
 * @category Array
 *
 * @param {*} smth array-like collection or object
 * @returns {Array} newly created array
 *
 * @example
 *     import {toArray} from '@yagni-js/yagni';
 *
 *     const obj = {0: 'foo', 1: 'baz', 2: 'bar', length: 3};
 *     const arr = toArray(obj);  // => ['foo', 'baz', 'bar']
 *
 */
function toArray(smth) {
  return Array.prototype.slice.call(smth);
}


/**
 * Takes an array as input and returns **first element** from it.
 *
 * @function
 * @category Array
 *
 * @param {Array} arr source array
 * @returns {*} first element from array or `undefined` if array is empty
 *
 * @example
 *     import {first} from '@yagni-js/yagni;
 *
 *     const arr = ['foo', 'baz', 'bar'];
 *     const foo = first(arr);  // => 'foo'
 *
 */
const first = pick(0);


/**
 * Takes an array as input and returns **it's length**.
 *
 * @function
 * @category Array
 *
 * @param {Array} arr source array
 * @returns {Number} length of array
 *
 * @example
 *     import {length} from '@yagni-js/yagni';
 *
 *     const arr = ['foo', 'baz', 'bar'];
 *     const len = length(arr);  // => 3
 *
 */
const length = pick('length');


/**
 * Takes a function `mapper` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **a new array**,
 * produced by applying `mapper` to each element of `arr`.
 *
 * Delegates to `map` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} mapper function to apply to each element of source array
 * @returns {Function} a new function to take an array `arr` as an argument
 * and produce a new array by applying `mapper` to each element of `array`
 *
 * @see pipe
 * @see mapObj
 *
 * @example
 *     import {map} from '@yagni-js/yagni';
 *
 *     function _add2(x) { return x + 2; }
 *     const add2 = map(_add2);
 *
 *     const src = [2, 5, 8];
 *     const dst = add2(src);  // => [4, 7, 10]
 *
 */
function map(mapper) {
  return function _map(arr) {
    return arr.map(mapper);
  };
}


/**
 * Takes a function `reducer` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns
 * **a new function**, which then takes some `initial` value as an argument
 * resulting **in a single output value**, produced by executing the specified
 * `reducer` function on each member of `arr` array.
 *
 * `reducer` function must have the following signature:
 *
 *     function reducer(accumulator, currentValue)
 *
 * and must return single output value.
 *
 * Delegates to `reduce` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} reducer function to iteratively apply to each element of
 * source array
 * @returns {Function} a new function to take `arr` as an argument and
 * produce another new function to take `initial` value and execute
 * `reducer` function over each member of the `arr` producing a single
 * output value
 *
 * @see pipe
 * @see reduceObj
 *
 * @example
 *     import {reduce} from '@yagni-js/yagni';
 *
 *     function reducer(acc, val) { return acc + val; }
 *     const sum = reduce(reducer);
 *     const values = [2, 5, 8];
 *     const overall = sum(values);
 *
 *     const res0 = overall(-15);  // => 0
 *     const res1 = overall(27);  // => 42
 *     const res2 = overall(73);  // => 88
 *
 */
function reduce(reducer) {
  return function _reduce(arr) {
    return function __reduce(initial) {
      return arr.reduce(reducer, initial);
    };
  };
}


/**
 * Takes a function `reducer` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and produces **a new array**
 * by executing the specified `reducer` function over each member
 * of `arr` array.
 *
 * `reducer` function must have the following signature:
 *
 *     function reducer(accumulator, currentValue)
 *
 * and must return an **array**.
 *
 * Delegates to `reduce` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} reducer function to iteratively apply to each element of
 * source array
 * @returns {Function} a new function to take `array` as an argument and
 * execute `reducer` function over each member of the `array` producing a new
 * array as output value
 *
 * @see filterMap
 * @see flatten
 * @see unique
 *
 * @example
 *     import {reduceToArr} from '@yagni-js/yagni';
 *
 *     function reducer(acc, val) { return val === 0 ? acc : acc.concat(val); }
 *     const excludeZeros = reduceToArr(reducer);
 *     const values = [2, 0, 5, 8, 0, 1];
 *
 *     const res = excludeZeros(values);  // => [2, 5, 8, 1]
 *
 */
function reduceToArr(reducer) {
  return function _reduceToArr(arr) {
    return arr.reduce(reducer, []);
  };
}


/**
 * Takes an array `arr` of functions as an argument
 * and returns **a new function**,
 * which then takes an `initial` value as an argument resulting in **a single
 * output value**, produced by iteratively executing each function from `array`
 * over the result of a previous function call.
 *
 * This is the **cornerstone** of `@yagni-js/yagni`.
 *
 * The idea for such implementation was borrowed from Elixir - you prepare
 * functions to be executed one after another and trigger the execution by
 * providing initial value.
 *
 * All functions to execute must be unary (must take only one argument) and
 * must return single output value.
 *
 * Delegates to `reduce` method of `arr` argument.
 *
 * @function
 * @category Array
 *
 * @param {Array} arr array of functions
 * @returns {Function} a new function to take `initial` value as an argument
 * and execute one by one function from source `array` producing a single
 * output value
 *
 * @see reduce
 *
 * @example
 *     import {pipe} from '@yagni-js/yagni';
 *
 *     function add2(x) { return x + 2; }
 *     function square(x) { return x * x; }
 *     function minus7(x) { return x - 7; }
 *
 *     const ops = pipe([
 *       add2,
 *       square,
 *       minus7
 *     ]);
 *
 *     const res0 = ops(5);  // => 42
 *     const res1 = ops(6);  // => 57
 *
 */
const pipe = reduce(
  function _pipe(acc, piper) {
    return piper(acc);
  }
);


/**
 * Promise-related version of `pipe` function.
 *
 * Takes an array `arr` of functions as an argument
 * and returns **a new function**,
 * which then takes an `initial` value as an argument resulting in **a single
 * output value** (an instance of Promise, ie. `thenable`),
 * produced by iteratively executing each function from `array`
 * over the result of a previous function call.
 *
 * All functions to execute must be unary (must take only one argument) and
 * must return single output value.
 *
 * `initial` value will be resolved using `Promise.resolve` method.
 * Functions to call will be passed to `Promise.then` method.
 *
 * NB. there is no way to handle errors within promises using this function.
 *
 * Delegates to `reduce` method of `arr` argument.
 *
 * @deprecated consider using `pipe` with `then` function
 * (for better error handling)
 *
 * @function
 * @category Array
 *
 * @param {Array} arr array of functions
 * @returns {Function} a new function to take `initial` value as an argument
 * and execute one by one function from source `array` producing a single
 * output value (an instance of Promise, ie. `thenable`)
 *
 * @example
 *     import {pipeP} from '@yagni-js/yagni';
 *
 *     function add2(x) { return x + 2; }
 *     function square(x) { return x * x; }
 *     function minus7(x) { return x - 7; }
 *
 *     const ops = pipeP([
 *       add2,
 *       square,
 *       minus7
 *     ]);
 *
 *     const res = ops(5);  // => resolved Promise with 42 as a result value
 *
 */
function pipeP(arr) {
  return function _pipeP(initial) {
    return arr.reduce(function (acc, piper) { return acc.then(piper); }, Promise.resolve(initial));
  };
}


/**
 * Takes a function `predicate` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **a new array**,
 * containing items from `arr` which satisfy `predicate`.
 *
 * Delegates to `filter` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} predicate function to check if an array item satisfies
 * the condition
 * @returns {Function} a new function to take an array `array` as an argument
 * and produce a new array containing items which satisfy `predicate`
 *
 * @example
 *     import {filter} from '@yagni-js/yagni';
 *
 *     function belowZero(x) { return x < 0; }
 *     const negatives = filter(belowZero);
 *
 *     const values = negatives([-1, 2, 4, 3, -3, -2, 0]);  // => [-1, -3, -2]
 *
 */
function filter(predicate) {
  return function _filter(arr) {
    return arr.filter(predicate);
  };
}


/**
 * Takes a function `predicate` and function `mapper` as arguments
 * and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **a new array**,
 * produced by applying `mapper` to such elements of `arr`, which satisfy
 * `predicate`.
 *
 * Delegates to `reduce` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} predicate function to check if an array item satisfies
 * the condition
 * @param {Function} mapper function to apply to satisfied elements of array
 * @returns {Function} a new function to take an array `arr` as an argument
 * and produce a new array by applying `mapper` to such elements of `arr`,
 * which satisfy `predicate`
 *
 * @example
 *     import {filterMap} from '@yagni-js/yagni';
 *
 *     function aboveZero(x) { return x > 0; }
 *     function square(x) { return x * x; }
 *
 *     const doublePositives = filterMap(aboveZero, square);
 *
 *     const values = doublePositives([-1, 1, -2, 2, -3, 3]);  // => [1, 4, 9]
 *
 */
function filterMap(predicate, mapper) {
  return reduceToArr(
    function _filterMap(acc, smth) {
      return predicate(smth) ? acc.concat(mapper(smth)) : acc;
    }
  );
}


/**
 * Takes an array `arr` as an argument and returns **a new function**,
 * which then takes some value `smth` as an argument and returns
 * **a new array**, produced by concatenating `arr` and `smth`.
 *
 * Delegates to `concat` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Array} arr source array
 * @returns {Function} a new function to take some value `smth` as an argument
 * and produce a new array by concatenating source `arr` with `smth`
 *
 * @example
 *     import {concat} from '@yagni-js/yagni';
 *
 *     const a = ['foo'];
 *     const b = ['baz'];
 *
 *     const c = concat(a);
 *
 *     const d = c(b);  // => ['foo', 'baz']
 *
 */
function concat(arr) {
  return function _concat(smth) {
    return arr.concat(smth);
  };
}


/**
 * Takes `separator` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **string**,
 * produced by concatenating all of the elements in `arr`,
 * separated by specified `separator`.
 *
 * If `separator` is not defined (`undefined` or `null`) `arr` will be
 * concatenated using *comma* as a separator.
 *
 * Delegates to `join` method of `arr` argument.
 *
 * @category Array
 *
 * @param {*} separator string to separate adjacent elements of array
 * @returns {Function} a new function to take array `arr` as an argument
 * and produce a string by concatenating all of the elements in `arr`
 * separated by `separator`
 *
 * @example
 *     import {join} from '@yagni-js/yagni';
 *
 *     const commaJoin = join();
 *     const dotJoin = join('.');
 *
 *     const data = ['foo', 'baz', 'bar'];
 *
 *     const res0 = commaJoin(data);  // => 'foo,baz,bar'
 *     const res1 = dotJoin(data);    // => 'foo.baz.bar'
 *
 */
function join(separator) {
  return function _join(arr) {
    return isDefined(separator) ? arr.join(separator) : arr.join();
  };
}


/**
 * Takes an array `arr` and produces **a new array** by taking all elements
 * from source `arr` and it's sub-arrays and placing them in a new array.
 *
 * Uses `concat` method of new array.
 *
 * @function
 * @category Array
 *
 * @param {Array} arr source array to flatten
 * @returns {Array} flattened version of source array
 *
 * @example
 *     import {flatten} from '@yagni-js/yagni';
 *
 *     const src = [[1, 2], [[3], 4, [[5]]]];
 *
 *     const dst = flatten(src);  // => [1, 2, 3, 4, 5]
 *
 */
const flatten = reduceToArr(
  function _flatten(acc, item) {
    return acc.concat(isArray(item) ? flatten(item) : item);
  }
);


/**
 * Takes a function `mapper` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and produces **a new array**
 * by taking all elements from source `arr` and it's sub-arrays,
 * applying `mapper` to them and placing the result in a new array.
 *
 * Uses `reduce` method of source array and `concat` method of new array.
 *
 * @category Array
 *
 * @param {Function} mapper function to apply to each element of new array
 * @returns {Function} a new function to take an array `arr` as an argument
 * and produce a new array by taking all elements from source `arr` and
 * it's sub-arrays, apply `mapper` to them and place the result in a new array
 *
 * @see flatten
 *
 * @example
 *     import {flattenMap} from '@yagni-js/yagni';
 *
 *     function square(x) { return x * x; }
 *
 *     const processor = flattenMap(square);
 *
 *     const src = [[1, 2], [[3], 4, [[5]]]];
 *
 *     const dst = processor(src);  // => [1, 4, 9, 16, 25]
 *
 */
function flattenMap(mapper) {
  return function _flattenMap(arr) {
    return arr.reduce(
      function __flattenMap(acc, item) {
        return acc.concat(isArray(item) ? _flattenMap(item) : mapper(item));
      },
      []
    );
  };
}


/**
 * Takes a function `predicate` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **true** if
 * all `arr` items satisfy `predicate` or **false** otherwise.
 *
 * Delegates to `every` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} predicate function to check if an array item satisfies
 * the condition
 * @returns {Function} a new function to take an array `arr` as an argument
 * and return `true` if all `arr` items satisfy `predicate` or `false` otherwise
 *
 * @example
 *     import {all} from '@yagni-js/yagni';
 *
 *     function below10(x) { return x < 10; }
 *     const allBelow10 = all(below10);
 *
 *     const res0 = allBelow10([2, 4, 6]);   // => true
 *     const res1 = allBelow10([12, 4, 6]);  // => false
 *
 */
function all(predicate) {
  return function _all(arr) {
    return arr.every(predicate);
  };
}


/**
 * Takes a function `predicate` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns **true** if
 * at least one `arr` item satisfy `predicate` or **false** otherwise.
 *
 * Delegates to `some` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Function} predicate function to check if an array item satisfies
 * the condition
 * @returns {Function} a new function to take an array `arr` as an argument
 * and return `true` if at least one `arr` item satisfy `predicate`
 * or `false` otherwise
 *
 * @example
 *     import {any} from '@yagni-js/yagni';
 *
 *     function below10(x) { return x < 10; }
 *     const anyBelow10 = any(below10);
 *
 *     const res0 = anyBelow10([10, 20, 30, 5, 40]);   // => true
 *     const res1 = anyBelow10([10, 20, 30, 40, 50]);  // => false
 *
 */
function any(predicate) {
  return function _any(arr) {
    return arr.some(predicate);
  };
}


/**
 * Takes `smth` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns
 * **the first index** at which `smth` can be found in the `arr` or -1 if
 * it is not present.
 *
 * Delegates to `indexOf` method of `arr` argument.
 *
 * @category Array
 *
 * @param {*} smth element to locate in array
 * @returns {Function} a new function to take array `arr` as an argument
 * and return the first index at which `smth` can be found in `arr` or -1 if
 * it is not present in `arr`
 *
 * @example
 *     import {index} from '@yagni-js/yagni';
 *
 *     const data = ['foo', 'baz', 'bar'];
 *
 *     const fooIndex = index('foo');
 *     const ftIndex = index(42);
 *
 *     const res0 = fooIndex(data);  // => 0
 *     const res1 = ftIndex(data);   // => -1
 *
 */
function index(smth) {
  return function _index(arr) {
    return arr.indexOf(smth);
  };
}


/**
 * Takes an array `arr` as an argument and returns **a new function**,
 * which then takes `smth` as an argument and returns
 * **the first index** at which `smth` can be found in the `arr` or -1 if
 * it is not present.
 *
 * Delegates to `indexOf` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Array} arr array to search for some element's index in
 * @returns {Function} a new function to take `smth` as an argument
 * and return the first index at which `smth` can be found in `arr` or -1 if
 * it is not present in `arr`
 *
 * @example
 *     import {indexIn} from '@yagni-js/yagni';
 *
 *     const data = ['foo', 'baz', 'bar'];
 *     const getIndexIn = indexIn(data);
 *
 *     const res0 = getIndexIn('foo');  // => 0
 *     const res1 = getIndexIn(42);     // => -1
 *
 */
function indexIn(arr) {
  return function _indexIn(smth) {
    return arr.indexOf(smth);
  };
}


/**
 * Takes `smth` as an argument and returns **a new function**,
 * which then takes an array `arr` as an argument and returns
 * **true** if `smth` is present in `arr` or **false** otherwise.
 *
 * Delegates to `indexOf` method of `arr` argument.
 *
 * @category Array
 *
 * @param {*} smth element to locate in array
 * @returns {Function} a new function to take array `arr` as an argument
 * and return true if `smth` was found in `arr` or false otherwise
 *
 * @example
 *     import {exists} from '@yagni-js/yagni';
 *
 *     const ftExists = exists(42);
 *
 *     const res0 = ftExists(['foo', 'baz', 'bar']);  // => false
 *     const res1 = ftExists(['foo', '42', 'bar']);   // => true
 *
 */
function exists(smth) {
  return pipe([
    index(smth),
    not(equals(-1))
  ]);
}


/**
 * Takes an array `arr` as an argument and returns **a new function**,
 * which then takes `smth` as an argument and returns
 * **true** if `smth` is present in `arr` or **false** otherwise.
 *
 * Delegates to `indexOf` method of `arr` argument.
 *
 * @category Array
 *
 * @param {Array} arr array to check some element is inside
 * @returns {Function} a new function to take `smth` as an argument
 * and return true if `smth` was found in `arr` or false otherwise
 *
 * @example
 *     import {existsIn} from '@yagni-js/yagni';
 *
 *     const isInside = existsIn(['foo', 'baz', 42]);
 *
 *     const res0 = isInside('foo');  // => true
 *     const res1 = isInside('bar');  // => false
 *     const res2 = isInside(42);     // => true
 *
 */
function existsIn(arr) {
  return pipe([
    indexIn(arr),
    not(equals(-1))
  ]);
}


/**
 * Takes an array `arr` and produces **a new array** by taking unique elements
 * from source `arr` and placing them in a new array.
 *
 * Uses `concat` and `indexOf` methods of new array.
 *
 * @function
 * @category Array
 *
 * @param {Array} arr source array to get unique elements from
 * @returns {Array} array with unique elements from `arr`
 *
 * @example
 *     import {unique} from '@yagni-js/yagni';
 *
 *     const src = [1, 2, 2, 3, 2, 3, 4, 4, 5];
 *
 *     const dst = unique(src);  // => [1, 2, 3, 4, 5]
 *
 */
const unique = reduceToArr(
  function _unique(acc, item) {
    return acc.indexOf(item) === -1 ? acc.concat(item) : acc;
  }
);

/**
 * Takes some value `smth` as an argument and returns it back.
 *
 * @category Function
 *
 * @param {*} smth some value
 * @returns {*} `smth`
 *
 * @example
 *
 *     import {identity} from '@yagni-js/yagni';
 *
 *     const foo = identity('foo');  // => 'foo'
 *
 */
function identity(smth) {
  return smth;
}


/**
 * Takes some value `smth` as an argument and returns **a new function**,
 * which when called always return `smth`.
 *
 * @category Function
 *
 * @param {*} smth some value
 * @returns {Function} a new function which when called always return `smth`
 *
 * @example
 *
 *     import {always} from '@yagni-js/yagni';
 *
 *     const answer = _.always(42);
 *
 *     const res0 = answer();       // => 42
 *     const res1 = answer('foo');  // => 42
 *     const res2 = answer('baz');  // => 42
 *     const res3 = answer(true);   // => 42
 *     const res4 = answer([12]);   // => 42
 *
 */
function always(smth) {
  return function _always() {
    return smth;
  };
}


/**
 * Lazily evaluates function result.
 *
 * Takes an unary function `caller` and some value `arg` for it and returns
 * **a new function**, which when called always returns the result of
 * evaluating `caller(arg)`.
 *
 * @category Function
 *
 * @param {Function} caller function to call
 * @param {*} arg some value as an argument for `caller`
 * @returns {Function} a new function to call and return the result of
 * `caller(arg)`
 *
 * @example
 *
 *     import {lazy} from '@yagni-js/yagni';
 *
 *     function add2(x) { return x + 2; }
 *
 *     const fixedPrice = lazy(add2, 40);
 *
 *     const res0 = fixedPrice();       // => 42
 *     const res1 = fixedPrice('foo');  // => 42
 *
 */
function lazy(caller, arg) {
  return function _lazy() {
    return caller(arg);
  };
}


/**
 * Takes a function or some value `smth` as a first argument and
 * some value `arg` as a second argument and returns result of calling
 * `smth(arg)` if `smth` is a function; or just `smth` if it's not a function
 *
 * @category Function
 *
 * @param {Function|*} smth function or some value
 * @param {*} arg argument for `smth` if it's a function
 * @returns {*} result of calling `smth(arg)` if `smth` is a function;
 * `smth` otherwise
 *
 * @see resultArr
 *
 * @example
 *
 *     import {result} from '@yagni-js/yagni';
 *
 *     function add2(x) { return x + 2; }
 *
 *     const res0 = result(42);             // => 42
 *     const res1 = result('foo', 42);      // => 'foo'
 *     const res2 = result(add2, 40);       // => 42
 */
function result(smth, arg) {
  return isFunction(smth) ? smth(arg) : smth;
}


/**
 * Takes an array `arr` of functions or some values as a first argument
 * and some value `arg` as a second argument and returns **a new array**,
 * produced by calling `result(item, arg)` over each element of `arr`.
 *
 * Uses `map` method of `arr` argument.
 *
 * @category Function
 *
 * @param {Array} arr array of functions or some values
 * @returns {Array} a new array produced by calling `result(item, arg)`
 * over each element of `arr`
 *
 * @see result
 *
 * @example
 *
 *     import {resultArr} from '@yagni-js/yagni';
 *
 *     const src = [
 *       'foo',
 *       function single(x) { return x; },
 *       function double(x) { return x * x; },
 *       function triple(x) { return x * x * x; },
 *       42];
 *
 *     const res = resultArr(src, 2);  // => ['foo', 2, 4, 8, 42]
 *
 */
function resultArr(arr, arg) {
  return arr.map(function _resultArr(smth) { return result(smth, arg); });
}


/**
 * Takes two functions `caller` and `argGetter` as arguments and returns
 * **a new function** which then takes some value `smth` as an argument
 * and returns result of calling `caller(argGetter(smth))`.
 *
 * @category Function
 *
 * @param {Function} caller target function to call
 * @param {Function} argGetter function to call to get an argument `arg`
 * @returns {Function} a new function to take some value `smth`, call
 * `argGetter(smth)` to get some value `arg` and return the result of calling
 * `caller(arg)`
 *
 * @example
 *
 *     import {fn, pick} from '@yagni-js/yagni';
 *
 *     function add2(x) { return x + 2; }
 *     const pickFoo = pick('foo');
 *
 *     const answer = fn(add2, pickFoo);
 *
 *     const src = {foo: 40};
 *
 *     const res = answer(src);  // => 42
 *
 */
function fn(caller, argGetter) {
  return function _fn(smth) {
    const param = argGetter(smth);
    return caller(param);
  };
}


/**
 * Takes three functions `caller`, `argGetter1` and `argGetter2`
 * as arguments and returns
 * **a new function** which then takes some value `smth` as an argument
 * and returns result of calling `caller(argGetter1(smth), argGetter2(smth))`.
 *
 * @category Function
 *
 * @param {Function} caller target function to call
 * @param {Function} argGetter1 function to call to get an argument `arg1`
 * @param {Function} argGetter2 function to call to get an argument `arg2`
 * @returns {Function} a new function to take some value `smth`, call
 * `argGetter1(smth)` and `argGetter2(smth)` to get some values
 * `arg1` and `arg2` and return the result of calling `caller(arg1, arg2)`
 *
 * @example
 *
 *     import {fn2, obj, pick} from '@yagni-js/yagni';
 *
 *     const pickFoo = pick('foo');
 *     const pickBaz = pick('baz');
 *
 *     const toObj = fn2(obj, pickFoo, pickBaz);
 *
 *     const src = {foo: 'key', baz: 'value'};
 *
 *     const res = toObj(src);   // => {key: 'value'}
 *
 */
function fn2(caller, arg1Getter, arg2Getter) {
  return function _fn2(smth) {
    const arg1 = arg1Getter(smth);
    const arg2 = arg2Getter(smth);
    return caller(arg1, arg2);
  };
}


/**
 * Takes some object `subj` as a first argument and `methodName` as a second
 * argument and returns **a new function**, which then takes some value `smth`
 * as an argument and returns result of calling `methodName` method of `subj`
 * using `smth` as an argument.
 *
 * @category Function
 *
 * @param {Object} subj owner of a method to call
 * @param {String} methodName method name
 * @returns {Function} a new function to take some value `smth` and return
 * the result of calling `methodName` method of `subj` using `smth` as an
 * argument
 *
 * @example
 *
 *     import {method} from '@yagni-js/yagni';
 *
 *     const stringify = method(JSON, 'stringify');
 *
 *     const src = {foo: 42, 'baz': true};
 *
 *     const res = stringify(src);  // => '{"foo":42,"baz":true}'
 *
 */
function method(subj, methodName) {
  return function _method(smth) {
    return subj[methodName](smth);
  };
}


/**
 * Takes two functions `fnGetter` and `argOrGetter` as arguments and returns
 * **a new function** which then takes some value `smth` as an argument
 * and:
 *   - calls `fnGetter(smth)` to get target function `caller` to call
 *   - calls `argOrGetter(smth)` to get an argument `arg` to use for `caller`
 *   - returns the result of `caller(arg)` call.
 *
 * `argOrGetter` can be a function or some static value to use as an `arg`
 * argument for `caller`.
 *