lens.js

import _curry2 from './internal/_curry2';
import map from './map';


/**
 * Returns a lens for the given getter and setter functions. The getter "gets"
 * the value of the focus; the setter "sets" the value of the focus. The setter
 * should not mutate the data structure.
 *
 * @func
 * @memberOf R
 * @since v0.8.0
 * @category Object
 * @typedefn Lens s a = Functor f => (a -> f a) -> s -> f s
 * @sig (s -> a) -> ((a, s) -> s) -> Lens s a
 * @param {Function} getter
 * @param {Function} setter
 * @return {Lens}
 * @see R.view, R.set, R.over, R.lensIndex, R.lensProp
 * @example
 *
 *      const xLens = R.lens(R.prop('x'), R.assoc('x'));
 *
 *      R.view(xLens, {x: 1, y: 2});            //=> 1
 *      R.set(xLens, 4, {x: 1, y: 2});          //=> {x: 4, y: 2}
 *      R.over(xLens, R.negate, {x: 1, y: 2});  //=> {x: -1, y: 2}
 */
var lens = _curry2(function lens(getter, setter) {
  return function(toFunctorFn) {
    return function(target) {
      return map(
        function(focus) {
          return setter(focus, target);
        },
        toFunctorFn(getter(target))
      );
    };
  };
});
export default lens;