hamishdickson / turtles

Recursive data types for scala

turtles

A well-known scientist (some say it was Bertrand Russell) once gave a public lecture on astronomy. He described how the earth orbits around the sun and how the sun, in turn, orbits around the center of a vast collection of stars called our galaxy. At the end of the lecture, a little old lady at the back of the room got up and said: "What you have told us is rubbish. The world is really a flat plate supported on the back of a giant tortoise." The scientist gave a superior smile before replying, "What is the tortoise standing on?" "You're very clever, young man, very clever," said the old lady. "But it's turtles all the way down!"

— Hawking, 1988

Recursive data types for scala

This project really is just for my own learning. Please have a look at slamdata's matryoshka for working and facinating implementations of these ideas

The implementations in this project are inspired by the classic paper, Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire

Catamorphism

scala> import turtles.list.instances._
import turtles.list.instances._

scala> import turtles.list.syntax._
import turtles.list.syntax._

scala> List(1,2,3,4).cata(0)(_ + _)
res1: Int = 10

Anamorphism

scala> import turtles.list.instances._
import turtles.list.instances._

scala> ana(0)(_ > 10)(_ + 1)
res2: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)