This is untested, am typing it up at work.
alias calc { if (!$0) return elseif ($isid) return $calc($1-) else echo $color(info) -at * [/calc] $1- = $calc($1-) }
Upon finally testing the above code I shortened it to one line.
alias calc if ($0) echo $color(info) -at * [/calc] $1- = $calc($1-)