Newcomer Examples

An example is worth a thousand words.

This section is dedicated to newcomers trying to figure out general idioms & conventions in Reason and BuckleScript. If you're a beginner who's got a good idea for an example, please suggest an edit!

Using the option type

option is a variant that comes with the standard library. It obviates the need for null values in other languages.

RE
let possiblyNullValue1 = None;
let possiblyNullValue2: option(string) = Some("Hello@");

switch (possiblyNullValue2) {
| None => print_endline("Nothing to see here.")
| Some(message) => print_endline(message)
};

Creating a parametrized type

RE
type universityStudent = {gpa: float};

type response('studentType) = {
  status: int,
  student: 'studentType
};

let result: response(universityStudent) = fetchDataFromServer();

Creating a JS Object

Assuming you're compiling to JavaScript.

RE
type payload = {
  name: string,
  age: int
};

let student1 = {
  name: "John",
  age: 30,
};

/* Compiles to a JS object with the above fields */

Modeling a JS Module with Default Export

See here.

Checking for JS nullable types using the option type

For a function whose argument is passed a JavaScript value that's potentially null or undefined, it's idiomatic to convert it to a Reason option. The conversion is done through the helper functions in Bucklescript's Js.Nullable module. In this case, toOption:

RE
let greetByName = (possiblyNullName) => {
  let optionName = Js.Nullable.toOption(possiblyNullName);
  switch (optionName) {
  | None => "Hi"
  | Some(name) => "Hello " ++ name
  }
};

This check compiles to possiblyNullName == null in JS, so checks for the presence of null or undefined.