I may have used a bad example to make my point.

Code:
alias test_eval {
  if ($1) {
    var %username = $1
  }
  var %moo = You are [username].
  echo -a Value of % $+ moo: %moo
  echo -a $eval($replacex(%moo, [username], % $+ username), 2)
}


This won't work.