Typing (2)

• Implicit static (invented in ML, 1977)

  • find out variable and function types based on their use, eg:
    • fact(x)= if x=0 then 1 else x*fact(x-1)
    • x compared with 0 implies x is a int
    • fact can return 1 implies fact returns a int
    • This inference works nicely with complex programs
  • pros:
    • as good type checking as explicit static
    • most of the expressivity of dynamic typing
  • cons: sometimes type error messages don't occur where you would except

Notes: