Lenses quick and dirty. Implementation and use. https://vimeo.com/104804647

1. Lenses Quick n’ Dirty

2. Agenda
• Review (Functors)
• Ideas behind lenses
• Neat Uses
• Demo

3. Functor Review

4. map(add(1), [1, 2, 3])
//=> [2, 3, 4]
map(add(1), {a: 1, b: 2})
//=> {a: 2, b: 3}

5. map(map(add(1)), Future.of(Maybe(2)))
//=> Future(Maybe(3))
map(map(add(1)), [Maybe(1), Maybe(2), Maybe(3)])
//=> [Maybe(2), Maybe(3), Maybe(4)]

6. Getters/Setters

7. map(f, Identity(x)) // Identity(f(x))
map(f, Const(x)) // Const(x) !noop

8. map(add(1), Identity(2))
//=> Identity(3)
map(add(1), Const(2))
//=> Const(2)

9. compose(runIdentity, map(add(1)), Identity)(2)
//=> 3
compose(getConst, map(add(1)), Const)(2)
//=> 2

10. var getter = function(f, x){
return compose(getConst, map(f), Const)(x)
}
var setter = function(f, x){
return compose(runIdentity, map(f), Identity)(x)
}
getter(reverse, [1,2,3])
//=> [1,2,3]
setter(reverse, [1,2,3])
//=> [3,2,1]

11. Lenses

12. LENS
A function that acts as both a getter and setter

13. var objectLens = function(key) {
return function(f, obj) {
return map(set(key, obj), f(obj[key]))
}
}

14. var objectLens = function(key) {
return function(f, obj) {
return map(set(key, obj), f(obj[key]))
}
}

15. var objectLens = function(key) {
return function(f, obj) {
return map(set(key, obj), f(obj[key]))
}
}

16. var view = function(lens, x) {
return compose(getConst, lens(Const))(x)
}
var over = function(lens, f, x) {
return compose(runIdentity, lens(compose(Identity, f)))(x)
}
var set = function(lens, v, x) {
return over(lens, K(v), x)
}

17. Uses

18. var L = makeLenses(['friends', ‘email’, ‘name’])
var user = {name: "Emily", friends: [{email: "bob@ross.net"}, {email: "kendra@spacehog.org"}] }
view(L.name, user)
//=> "Emily"
view(L.friends, user)
//=> [{email: "bob@ross.net"}, {email: "kendra@spacehog.org}]
over(L.name, replace("E", "***"), user)
//=> {name: "***mily", friends: [{email: "bob@ross.net"}, {email: "kendra@spacehog.org}] }

19. set(L.name, “Esmeralda”, user)
//=> {name: "Esmeralda", friends: [{email: "bob@ross.net"}, {email: "kendra@spacehog.org}] }
set(L.friends, [], user)
//=> //=> {name: "Emily", friends: [] }

20. var user = {name: "Emily", friends: [undefined, {email: "bob@ross.net"}, undefined, {email: "kendra@spacehog.var getUser = compose(sendJSON, filter(isDefined), _.get(‘friends'))
getUser(user)
//=> [{email: "bob@ross.net"}, {email: “kendra@spacehog.org}]

21. var user = {name: "Emily", friends: [undefined, {email: "bob@ross.net"}, undefined, {email: "kendra@spacehog.var getUser = compose(sendJSON, over(L.friends, filter(isDefined)))
getUser(user)
//=> {name: "Esmeralda", friends: [{email: "bob@ross.net"}, {email: "kendra@spacehog.org}] }

22. L.firstFriend = compose(L.friends, L.num(0));
set(L.firstFriend, {email:"kelly@kapowski.net"}, user)
//=> {name: "Emily", friends: [{email: "kelly@kapowski.net"}, {email: "kendra@spacehog.org}] }
L.firstFriendsEmail = compose(L.firstFriend, L.email);
over(L.firstFriendsEmail, toUpperCase, user)
//=> {name: "Emily", friends: [{email: “KELLY@KAPOWSKI.NET"}, {email: "kendra@spacehog.org}]

23. L.friendsEmails = compose(L.friends, L.mapped, L.email)
var emailFriends = compose( concat("Emailed friends of ")
, view(L.name)
, over(L.friendsEmails, sendEmail)
)
emailFriends(user)
//=> emailing bob@ross.net
//=> emailing kendra@spacehog.org
//=> Emailed friends of Emily