02 Variants

Variants are a new way to build data types.

Perhaps you've seen a type that allows you to enumerate through constants, like an enum.

You can do something similar with variants.

type primary_color = Red | Green | Blue

type primary_color = Red | Green | Blue

let r = Red

val r : primary_color = Red

See, we have a type primary_color now!

Let's make a variant for shapes!

type point = float * float

type shape =
	(* lets represent a circle by it's center and it's radius*)
	(* we can use the "of" keyword to make it carry more data*)
	| Circle of {center: point; radius: float}
	(* let's represent rectangles with their lower left
	coordinate and their upper right coordiante.*)
	| Rectangle of {lower_left: point; upper_right: point}

type point = float * float

type shape =
    Circle of { center : point; radius : float; }
  | Rectangle of { lower_left : point; upper_right : point; }

Now let's make a rectangle and a circle!

let c1 = Circle {center = (0., 0.); radius = 1.}

val c1 : shape = Circle {center = (0., 0.); radius = 1.}

let r1 = Rectangle {lower_left = (-1., -1.); upper_right = (1., 1.)}

val r1 : shape = Rectangle {lower_left = (-1., -1.); upper_right = (1., 1.)}

These variables now carry all the data we need to represent our points!