regression/local-ref.sml

   1
   2 local
   3    val c = ref 0
   4 in
   5    fun fib n
   6      = let
   7           val _ = if !c mod 5 = 0
   8                     then print (concat [Int.toString (!c),
   9                                         "th invocation of fib\n"])
  10                     else ()
  11           val _ = c := !c + 1
  12        in
  13           case n
  14             of 0 => 1
  15              | 1 => 1
  16              | n => (fib (n-1)) + (fib (n-2))
  17        end
  18 end
  19
  20 val n = fib 5
  21
  22 val _ = print (concat ["fib(5) = ", Int.toString n, "\n"])