How to generate all permutations of some numbers with a low heap allocation and without try-fail

permutations.R

get.perm = function(n, FUN = print) {
  perm = n:1

  switch_loop = function(L) {
    # evaluate all pair exchanges on the given level (L)
    if (L == 1)
      FUN(perm)
    else {
      switch_pair = function(i1, i2) {
        temp = perm[i1]
        perm[i1] <<- perm[i2]
        perm[i2] <<- temp
      }

      for(i in 1:L) {
        if (i > 1)
          # switch to involve something new from level L
          switch_pair((i - 1), L)

        # allow lower level items to vary
        switch_loop(L - 1)

        if (i > 1)
          # switch back
          switch_pair((i - 1), L)
      }
    }
  }

  switch_loop(n)
}

perms = c()
get.perm(5,
         FUN = function(perm) perms <<- rbind(perms, perm))
print(perms)