is-prime.shen

(datatype is-prime
   if (is-prime? N)
   N : number;
   ==============
   N : prime;)

(define is-prime?
  2 -> true
  X -> (prime* X (/ X 2) 2) where (number? X)
  _ -> false)

(define prime*
  X Max Div -> false	where (integer? (/ X Div))
  X Max Div -> true	where (> Div Max)
  X Max Div -> (prime* X Max (+ 1 Div)))

\* 
Sample REPL interaction:
(12-) (tc +) \* Turn on the type checker. *\
true
(13+) 1 : prime
1 : prime
(14+) 2 : prime
type error
*\