Abstract: Build a utility function that takes an object path, and constructs a Lens for it.
Someone asked in gitter.im for an alternative to `assocPath` that takes a function instead of a value. I recommended Lenses, e.g.
var R = require('ramda');
var myObj = { a: { b: 2 } };
var aLens = R.lensProp('a');
var bLens = R.lensProp('b');
var overA = R.over(aLens);
var overB = R.over(bLens);
var myFn = R.inc;
overA(overB(myFn))(myObj); //=> { a: { b: 3 } }
@CrossEye mentioned an improvement to the example above. Lenses are composable!! O.O
var deepLens = R.compose(aLens, bLens);
R.over(deepLens, myFn, myObj) //=> { a: { b: 3} }
Let's see if we can do better.
Attempt 1:
Create one lens for the overall object path.
// [String] -> Lens s a
var lensPath = function (path) {
var getter = R.path(path);
var setter = R.assocPath(path);
return R.lens(getter, setter);
}
var deepLens = lensPath(['a', 'b']);
var result = R.over(deepLens, myFn, myObj);
console.log(result, myObj);
And my work here is done. (>.>)
var toJson = R.nAry(1, JSON.stringify);
var test = R.curry(function (input, fn, expected, name) {
var actual = fn(input);
var passes = R.equals(expected, actual);
if (passes)
return R.concat(name, ': pass');
else
return R.join(' ', [name, ': fail -- expected: ', toJson(expected), ' -- actual: ', toJson(actual)]);
});
var testWithObj = test(myObj);
var testView = testWithObj(R.view(deepLens), 2, 'test view');
var expected = { a: { b: 4 } };
var testSet = testWithObj(R.set(deepLens, 4), expected, 'test set');
var expected = { a: { b: 3 } };
var testOver = testWithObj(R.over(deepLens, R.inc), expected, 'test over');
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