How do I declare a map type in Reason ML?

Question

One advantage of Reason ML over JavaScript is that it provides a Map type that uses structural equality rather than reference equality.

However, I cann

Answer 1

If you're just dealing with a Map, Belt's Map.String would do the trick.

module MS = Belt.Map.String;

let foo: MS.t(int) = [|("a", 1), ("b", 2), ("c", 3)|]->MS.fromArray;

The ergonomics around the Belt version are a little less painful, and they're immutable maps to boot! There's also Map.Int within Belt. For other key types, you'll have to define your own comparator. Which is back to something similar to the two step process @glennsl detailed above.