F#模块

//Top-level module declaration.
module [accessibility-modifier] [qualified-namespace.]module-name
	declarations
//Local module declaration.
module [accessibility-modifier] module-name =
    declarations

module Arithmetic = 
 let add a b =
  a+b
 let sub a b =
  a-b
 let mul a b = 
  a*b
 let div a b =
  a/b

printf "%d" (Arithmetic.add 10 20)

open Arithmetic
printf "%d" (sub 20 10)