[AlenaKazakova]

Could you please explain how exactly do you want type checking to be done?
Is it like this:
(provide (contract-out [add (-> number? number? number?)]))
?
I couldn't find it on the lecture slides.

[김윤승]

Do it like page 108 of the "Part 1: For lecture" slide, which is:

{= : int * int -> bool}
{* : int * int -> int}
{- : int * int -> int}
{(define (fac {n : int})
{(if {(= {n : int} {0 : int}) : bool}
{1 : int}
{(* {n : int}
{(fac {(- {n:int} {1:int}) : int}) : int}
) : int}
) : int}
) : int -> int}

[AlenaKazakova]

I saw this, but #lang racket does not understand the notation. Why is that?

Thank you.

[김윤승]

That's the right way. We are not going to run the program. We will just read it.