Web Development with ReasonML

Getting Another Perspective

If you’re still a bit uncertain of what Belt.Option.map and Belt.Option.flatMap do, here’s what they’d look like if we were to implement them ourselves:

datatypes/src/BeltExamples.re

let myMap = (optValue: option('a), f: ('a) => 'b) : option('b) => {
  switch (optValue) {
    | Some(value) => Some(f(value))
    | None => None
  }
};

let myFlatMap = (optValue: option('a), f: ('a) => option('b)) :
 option('b) => {
  switch (optValue) {
    | Some(value) => f(value)
    | None => None
  }
};

The annotation f: (’a) => option(’b) signifies a function taking a parameter of type ’a and returning a value of type option(’b).

Similarly, ...