math example: combination

perm.erl

-module(perm).
-export([main/1]).

iend(M, N, Level) ->
  Room = N - Level,
  M - Room.

for(S, E, F) when S =< E -> F(S), for(S + 1, E, F);
for(_, _, _) -> void.

test(L, M, N, T, Cur, Level) when M >= N ->
  for(Cur, iend(M, N, Level), fun(I) ->
    T2 = [lists:nth(I, L) | T],
    if
      Level =/= N -> test(L, M, N, T2, I + 1, Level + 1);
      true -> io:format("~p~n", [lists:reverse(T2)])
    end
  end).

main([]) ->
  L = [1,2,3,4,5,6],
  test(L, length(L), 3, [], 1, 1).

perm.lua

local L = {1,2,3,4,5,6}
local M = #L
local N = 3

function iend(M, N, level)
  local room = N - level
  return M - room
end

function dup(T)
  return {table.unpack(T)}
end

function test(L, M, N, T, cur, level)
  T = T or {}
  cur = cur or 1
  level = level or 1

  for i = cur, iend(M, N, level) do
    T[level] = L[i]
    if level ~= N then
      test(L, M, N, dup(T), i + 1, level + 1)
    else
      for i, v in ipairs(T) do
        io.write(v)
        io.write("\t")
      end
      print""
    end
  end
end

print""
test(L, M, N)