Today I Learned

A Hashrocket project

Create A Stream From An Array In ReasonML

There are functions in the Stream module for turning a variety of data structures into streams — lists, input channels, etc.

What if you have an array?

The Stream.from function lets you define a function for custom fitting data structures into streams. Let’s take a look:

let pokemons = [| "bulbasaur", "charmander", "squirtle" |];

let poke_stream: Stream.t(string) =
  Stream.from(i =>
    switch (pokemons[i]) {
    | pokemon => Some(pokemon)
    | exception (Invalid_argument("index out of bounds")) => None
    }
  );

The function takes the current index and needs to either return Some('a) with the corresponding value or None if the stream is empty.

With that, we now have a stream on which we can invoke any of the stream functions.

switch (Stream.next(poke_stream)) {
| pokemon => print_endline(Printf.sprintf("Next Pokemon: %s", pokemon))
| exception Stream.Failure => print_endline("No pokemon left")
};