Subtyping -- examples

 

  type any = { }
  type entity = { age : int }
  type vehicle = { age : int, speed : int }
  type machine = { age : int, fuel : string }
  type car = { age : int, speed : int, fuel : string }

Subtyping rules

  • %t <= %t
  • \ffrac{ %s_1 <= %t_1, ..., %s_n <= %t_n }{ { a_1 : %s_1, ..., a_{n + m} : %s_{n + m} } <= { a_1 : %t_1 , ..., a_n : %t_n } }
slide: Examples of object subtyping