lua/test/factorial.lua

   1 -- function closures are powerful
   2
   3 -- traditional fixed-point operator from functional programming
   4 Y = function (g)
   5       local a = function (f) return f(f) end
   6       return a(function (f)
   7                  return g(function (x)
   8                              local c=f(f)
   9                              return c(x)
  10                            end)
  11                end)
  12 end
  13
  14
  15 -- factorial without recursion
  16 F = function (f)
  17       return function (n)
  18                if n == 0 then return 1
  19                else return n*f(n-1) end
  20              end
  21     end
  22
  23 factorial = Y(F)   -- factorial is the fixed point of F
  24
  25 -- now test it
  26 function test(x)
  27         io.write(x,"! = ",factorial(x),"\n")
  28 end
  29
  30 for n=0,16 do
  31         test(n)
  32 end