OCaml |> operator

Question

Could someone explain what the |> operator does? This code was taken from the reference here:

let m = PairsMap.(empty |> add (0,1) \"hello\" |> add (1,         


        

Answer 1

Module.(e) is equivalent to let open Module in e. It is a shorthand syntax to introduce things in scope.

The operator |> is defined in module Pervasives as let (|>) x f = f x. (In fact, it is defined as an external primitive, easier to compile. This is unimportant here.) It is the reverse application function, that makes it easier to chain successive calls. Without it, you would need to write

let m = PairsMap.(add (1,0) "world" (add (0,1) "hello" empty))

that requires more parentheses.