Kickstart your app with lenses

lenses.swift

struct Dog {
    var name: String
}

struct Person {
    var name: String
    var age: Int
    var dog: Dog
}

var dog = Dog(name: "Bark")
var person = Person(name: "Foo", age: 12, dog: dog)

struct Lens<Whole, Part> {
    let get: (Whole) -> Part
    let set: (Part) -> (Whole) -> Whole
}

extension Person {
    
    enum lens {
        static let dog: Lens<Person, Dog> = Lens(
            get: { person in return person.dog },
            set: { newDog in
                return { person in
                    var newPerson = person
                    newPerson.dog = newDog
                    return newPerson
                }
                
        })
        
        static let age: Lens<Person, Int> = Lens(
            get: { person in return person.age},
            set: { newAge in
                return { person in
                    var newPerson = person
                    newPerson.age = newAge
                    return newPerson
                }
                
        })
        
        static let name: Lens<Person, String> = Lens.init(
            get: { whole in return whole.name },
            set: { newPart in {
                oldWhole in
                var whole = oldWhole
                whole.name = newPart
                return whole
            }})

        
    }
}

extension Dog {
    enum lens {
        static let name: Lens<Dog, String> = Lens.init(
            get: { whole in return whole.name },
            set: { newPart in {
                oldWhole in
                var whole = oldWhole
                whole.name = newPart
                return whole
                }})

    }
}

//print(Person.lens.dog.get(person))
//let newDog = Dog(name: "Reksio")
//let function: (Person) -> Person = Person.lens.dog.set(newDog)
//print(function(person))

///
///
///

precedencegroup PipelineOperator {
    associativity: left
}
infix operator |> : PipelineOperator

func |> (lhs: Person, rhs: (Person) -> Person) -> Person {
    return rhs(lhs)
}

let newPerson = person
    |> Person.lens.name.set("Astek")
    |> Person.lens.age.set(30)
    |> Person.lens.dog.set(Dog(name: "Kik"))

//print(newPerson)

///

precedencegroup SetOperator {
    associativity: none
    higherThan: PipelineOperator
}
infix operator .~ : SetOperator
infix operator %~ : SetOperator

extension Lens {
    static func .~ (lhs: Lens<Whole, Part>, rhs: Part) -> (Whole) -> Whole {
        return { whole in
            return lhs.set(rhs)(whole)
        }
        
    }
        
    static func %~ (lhs: Lens<Whole, Part>, rhs: @escaping (Part) -> Part) -> (Whole) -> Whole {
            return { whole in
            let part = lhs.get(whole)
            let newPart = rhs(part)
            let newWhole = lhs.set(newPart)(whole)
            return newWhole
    }
        }
}


let newPerson2 = person
    |> Person.lens.name .~ "Eliasz"
    |> Person.lens.age %~ { age in return age * 2}
    |> Person.lens.dog .~ Dog(name: "Olo")

print(newPerson2)

//Lens<A, B> + Lens<B, C> = Lens<A, C>
precedencegroup ChainOperator {
    associativity: left
    higherThan: SetOperator
}
infix operator .. : ChainOperator

//Whole
//    Part
//        Subpart
extension Lens {
    static func .. <Subpart>(lhs: Lens<Whole, Part>, rhs: Lens<Part, Subpart>) -> Lens<Whole, Subpart> {
       return Lens<Whole, Subpart>.init(
        get: { whole in
            let part = lhs.get(whole)
            let subpart = rhs.get(part)
            return subpart
       },
        set: { newSubpart in
            return { whole in
                let part = lhs.get(whole)
                let newPart = rhs.set(newSubpart)(part)
                let newWhole = lhs.set(newPart)(whole)
                return newWhole
            }
       })
    }
}

let dogsName: Lens<Person, String> = Person.lens.dog..Dog.lens.name

extension Person {
    enum deepLens {
        static let dogsName = Person.lens.dog..Dog.lens.name
    }
}

let newPerson3 = person
    |> Person.lens.name .~ "Test"
    |> Person.lens.age %~ { age in return age * 2}
    |> Person.deepLens.dogsName .~ "XX"

print(newPerson3)