Why loop?

alias nickSearch {
  if ($isid && $me ison $1 && $3 isnum 1-) {
    unset %::nickSearch
    set -u0 %::nickSearchDelimiter $chr($3)
    filter -lk $1 _nicksearch $2
    if ($4) return $sorttok(%::nickSearch, $3)
    return %::nickSearch
  }
}
alias -l _nickSearch  set -u0 %::nickSearch $addtok(%::nickSearch, $1, %::nickSearchDelimiter)

(updated for a bit more speed; but at the cost of characters)