swap = function(x,y)
{
  if (!exist($$.[x]))
  { return 0; }
  if (!exist($$.[y]))
  { return 0; }
  local (t);
  t = $$.[x];
  $$.[x] = $$.[y];
  $$.[y] = t;
  return 1;
};

>>  a=1
1
>>  b = "fish"
fish
>> swap( "a" , "b" );
>>  a
fish
>>  b
1