In Reason

    let sum = (a, b) => a + b;

actually accepts only arguments of type int, not any numeric type. The + operator is defined as

    let (+): (int, int) => int;

To have the function accept floats, for example, you would have to use the +. operator like this

    let sum = (a, b) => a +. b;

I noticed the article had a tendency to compare numbers in Typescript with integers in ReasonML, and I was wondering why.

I guess a clearer distinction between the two can be nice, but then how does that compile to javascript?

ReasonML ints and floats both compile to JavaScript numbers. See https://bucklescript.github.io/docs/en/common-data-types#sha... for a type mapping table.