$ include "seed7_05.s7i";

const type: permutations is array array integer;

const func permutations: permutations (in array integer: items) is func
  result
    var permutations: permsList is 0 times 0 times 0;
  local
    const proc: perms (in array integer: sequence, in array integer: prefix) is func
      local
        var integer: element is 0;
        var integer: index is 0;
      begin
        if length(sequence) <> 0 then
          for element key index range sequence do
            perms(sequence[.. pred(index)] & sequence[succ(index) ..], prefix & [] (element));
          end for;
        else
          permsList &:= prefix;
        end if;
      end func;
  begin
    perms(items, 0 times 0);
  end func;

const proc: main is func
  local
    var array integer: perm is 0 times 0;
    var integer: element is 0;
  begin
    for perm range permutations([] (1, 2, 3)) do
      for element range perm do
        write(element <& " ");
      end for;
      writeln;
    end for;
  end func;