view.js•1.04 kB
var _curry2 = require('./internal/_curry2');
/**
* Returns a "view" of the given data structure, determined by the given lens.
* The lens's focus determines which portion of the data structure is visible.
*
* @func
* @memberOf R
* @since v0.16.0
* @category Object
* @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
* @sig Lens s a -> s -> a
* @param {Lens} lens
* @param {*} x
* @return {*}
* @see R.prop, R.lensIndex, R.lensProp
* @example
*
* var xLens = R.lensProp('x');
*
* R.view(xLens, {x: 1, y: 2}); //=> 1
* R.view(xLens, {x: 4, y: 2}); //=> 4
*/
module.exports = (function() {
// `Const` is a functor that effectively ignores the function given to `map`.
var Const = function(x) {
return {value: x, map: function() { return this; }};
};
return _curry2(function view(lens, x) {
// Using `Const` effectively ignores the setter function of the `lens`,
// leaving the value returned by the getter function unmodified.
return lens(Const)(x).value;
});
}());