You could use it as an identifer so to speak, this way if there is an error, the calling script will be able to handle it:

alias for {
  if ($0 != 2 || $1. !isnum 0- || $2 == $null) return * /For: Invalid parameters

  var %n = $1
  while (%n) {
    if ($try($2-)) return $v1 
    dec %n
  }

}
alias try $1- | :error | if ($error) reseterror | return $v1

;---------------;
;--- Example ---;
;---------------;
alias for:exp {

  ;These two will throw errors!
  if ($for(a,)) echo -a Error: $v1
  if ($for(1,!write)) echo -a Error: $v1

  ;if $for(,) returns null, it succeeded
  if (!$for(2,echo -a hey!)) echo -a Success!
}

Edited to add some more error checking & to clean up the code