Fantasy Lenses
Lenses are composable, immutable getters and setters. Composable in that they allow updating of nested data structures. Immutable in that the setters return copies of the whole data structure.
Examples
Nested updating
var person = {
name: "Brian McKenna",
location: {
number: 1006,
street: "Pearl St",
postcode: 80302
}
},
objectLens = require('fantasy-lenses').Lens.objectLens,
locationLens = objectLens('location'),
numberLens = objectLens('number'),
store = locationLens.andThen(numberLens).run(person);
console.log(store.get());
// 1006
console.log(store.set(1007));
// { name: 'Brian McKenna',
// location: { number: 1007, street: 'Pearl St', postcode: 80302 } }Accessing optional fields
var data = [{
name: "First record",
config: {
type: 2
}
}, {
description: "Hello world",
config: {
type: 3
}
}, {
name: "Third record"
}],
objectLens = require('fantasy-lenses').PartialLens.objectLens,
configLens = objectLens('config'),
typeLens = objectLens('type'),
configTypeLens = configLens.andThen(typeLens);
console.log(data.filter(function(o) {
return configTypeLens.run(o).fold(
function(store) {
// Get the field's content
return store.get() == 2;
},
function() {
// Didn't find field
return false;
}
);
}));
// [ { name: 'First record', config: { type: 2 } } ]