ReasonML Quick Start Guide

Exploring Reason

Ask yourself whether the following is a statement or an expression:

let foo = "bar";

In JavaScript, it's a statement, but in Reason, it's an expression. Another example of an expression is 4 + 3, which can also be represented as 4 + (2 + 1).

Many things in Reason are expressions, including control structures such as if-else, switch, for and while:

let message = if (true) {  "Hello"} else {  "Goodbye"};

We also have ternaries in Reason. Here is another way to express the preceding code:

let message = true ? "Hello" : "Goodbye";

Even anonymous block scopes are expressions that evaluate to the last line's expression:

let message = {  let part1 = "Hello";  let part2 = "World";  {j|$part1 $part2|j};};/* message evaluates to "Hello ...