Data Lenses/Optics?

[vknabel]

What are Lenses/Optics?

Lenses bundle the access to a specific property of a value for read and write operations.
Especially in programming languages which do not serve real mutability of values or objects, every little change of value requires the developer to make a copy.

Especially when working with bigger types, this especially leads developer to write lots of repetitive code.
Lenses try to reduce this overhead.

Example

Probably a lens in Lithia could be declared as follows:

data Lens {
  get from
  over changeValue, from
}

Let's image we have a person:

data Person {
  name
  age
}

And we want a function which ages the person by one year:

func age { person =>
  Person person.name, person.age + 1
}

The bigger the data type grows, the bigger our function. With lenses we could reduce the overhead:

let age = Person.age { age => age + 1 }

// Person.age would be:
personAgeLens = Lens { p => p.age }, { changeAge, person => 
  Person person.name, changeAge person.age
}

Benefits

• Reduces developer overhead

Drawbacks

• A simple, but a new language feature to support