let a = 10
let b = 10
let c = a + b
let x = 1 and y = 2
Js.log(x + y) // 3
// block scope
// z = 3
let z = {
let x = 1
let y = 2
x + y
}
// shadow
let x = 1
let x = 2
let x = 3
Js.log(x) // 3
let x = ref (10)
x := x.contents + 1
x.contents = x.contents + 1 /* x is 12 */
type box<'a> = {mutable contents: 'a}
let box = v => {contents: v}
let r = box(10)
r.contents = r.contents + 1