# Combinators: `map`

`match` is a valid method for handling `Option`s. However, you may eventually find heavy usage tedious, especially with operations only valid with an input. In these cases, combinators can be used to manage control flow in a modular fashion.

`Option` has a built in method called `map()`, a combinator for the simple mapping of `Some -> Some` and `None -> None`. Multiple `map()` calls can be chained together for even more flexibility.

In the following example, `process()` replaces all functions previous to it while staying compact.

``````#![allow(dead_code)]

#[derive(Debug)] enum Food { Apple, Carrot, Potato }

#[derive(Debug)] struct Peeled(Food);
#[derive(Debug)] struct Chopped(Food);
#[derive(Debug)] struct Cooked(Food);

// Peeling food. If there isn't any, then return `None`.
// Otherwise, return the peeled food.
fn peel(food: Option<Food>) -> Option<Peeled> {
match food {
Some(food) => Some(Peeled(food)),
None       => None,
}
}

// Chopping food. If there isn't any, then return `None`.
// Otherwise, return the chopped food.
fn chop(peeled: Option<Peeled>) -> Option<Chopped> {
match peeled {
Some(Peeled(food)) => Some(Chopped(food)),
None               => None,
}
}

// Cooking food. Here, we showcase `map()` instead of `match` for case handling.
fn cook(chopped: Option<Chopped>) -> Option<Cooked> {
chopped.map(|Chopped(food)| Cooked(food))
}

// A function to peel, chop, and cook food all in sequence.
// We chain multiple uses of `map()` to simplify the code.
fn process(food: Option<Food>) -> Option<Cooked> {
food.map(|f| Peeled(f))
.map(|Peeled(f)| Chopped(f))
.map(|Chopped(f)| Cooked(f))
}

// Check whether there's food or not before trying to eat it!
fn eat(food: Option<Cooked>) {
match food {
Some(food) => println!("Mmm. I love {:?}", food),
None       => println!("Oh no! It wasn't edible."),
}
}

fn main() {
let apple = Some(Food::Apple);
let carrot = Some(Food::Carrot);
let potato = None;

let cooked_apple = cook(chop(peel(apple)));
let cooked_carrot = cook(chop(peel(carrot)));
// Let's try the simpler looking `process()` now.
let cooked_potato = process(potato);

eat(cooked_apple);
eat(cooked_carrot);
eat(cooked_potato);
}``````