Source code in the pl/i programming language

factorial: procedure (N) returns (fixed decimal (30));
   declare N fixed binary nonassignable;
   declare i fixed decimal (10);
   declare F fixed decimal (30);

   if N < 0 then signal error;
   F = 1;
   do i = 2 to N;
      F = F * i;
   end;
   return (F);
end factorial;