lens.js•1.12 kB
var _curry2 = require('./internal/_curry2');
var map = require('./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
*
* var 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}
*/
module.exports = _curry2(function lens(getter, setter) {
return function(toFunctorFn) {
return function(target) {
return map(
function(focus) {
return setter(focus, target);
},
toFunctorFn(getter(target))
);
};
};
});