fun prime(n)=
       let 
	exception NeitherPrimeNorComposite;
	exception NegativeNumber;
	fun smallestdivisor(n) =
               let 
		fun finddiv(n,tester)=if tester*tester > n then n
                                     else if n mod tester = 0 then tester
                                     else finddiv(n,tester+2);
               in finddiv(n,3) 
		end;
       in if n=1 then raise NeitherPrimeNorComposite 
	   else if n<0 then raise NegativeNumber 
	   else if n=2 then true 
	   else if n mod 2 = 0 then false 
	   else if n = smallestdivisor(n) then true 
	   else false 
	end;