procedure main(A)
   every write("fib(",a := numeric(!A),")=",fib(a))
end

procedure fib(n)
   local  source, i
   static cache
   initial {
      cache := table()
      cache[0] := 0
      cache[1] := 1
      }
   if type(n) == "integer" & n >= 0 then
      return n @ makeProc {{
         i := @(source := &source)                                          # 1
         /cache[i] := ((i-1)@makeProc(^&current)+(i-2)@makeProc(^&current)) # 2
         cache[i] @ source                                                  # 3
         }}
end

procedure makeProc(A)
   A := if type(A) == "list" then A[1]
   return (@A, A)                    # prime and return
end