gadt.re

type state = int;

type action =
  | Inc
  | IncBy int
  | Dec
  | DecBy int
  | Reset;

let update state action =>
  switch action {
  | Inc => state + 1
  | IncBy n => state + n
  | Dec => state - 1
  | DecBy n => state - n
  | Reset => 0
  };