Web Development with ReasonML

Using Variant Data Types

Let’s say that a small shirt costs $11.00, a medium costs $12.50, a large costs $14.00, and an extra-large costs $16.00. We can write a function to return the price of a shirt given its size:

datatypes/src/ShirtSizes.re

let priceIf = (size: shirtSize) : float => {
  if (size === Small) {
    11.00
  } else if (size === Medium) {
    12.50
  } else if (size === Large) {
    14.00
  } else {
    16.00
  }
};

Js.log(priceIf(mySize)); /* output: 12.5 */
Js.log(priceIf(otherSize)); /* output: 14 */

But it’s much more common in ReasonML to use a switch expression to pattern match the size:

datatypes/src/ShirtSizes.re

let price = (size: shirtSize) : float