1) GADT, 2) Variants in usage of ReasonML/OCaml pipes

Pipe_Usage_Variants.re

/*
 * Variants in usage of ReasonML/OCaml pipes
 */

type attributeType('t) =
  | Lastname: attributeType(string)
  | ZipCode: attributeType(int);

type recordType = {
  lastname: string,
  zipCode: int,
};

let getString: type t. (recordType, attributeType(t)) => string =
  (record, attr) =>
    switch (attr) {
    | Lastname => record.lastname
    | ZipCode => string_of_int(record.zipCode)
    };

// example record
let john = {lastname: "John", zipCode: 8500};

// 9 variants of the same result:
// getting John's ZipCode as a string
let _: string = getString(john, ZipCode);
let _: string = john->getString(ZipCode);
let _: string = john->getString @@ ZipCode;
let _: string = (john |> getString)(ZipCode);
let _: string = (john |> getString) @@ ZipCode;
let _: string = ZipCode |> getString @@ john;
let _: string = ZipCode |> getString(john);
let _: string = ZipCode |> john->getString;
let _: string = ZipCode |> (john |> getString);