Not a bad idea at all. Btw, I'd also like a second parameter to $calc, which would be able to do int-ing and rounding. It would be a number; -1 (or smaller/non-numeric) would do int-ing, 0 and greater would do rounding.
$calc(5 / 3,0) = $round($calc(5 / 3),0) = 2
$calc(5 / 3,1) = $round($calc(5 / 3),1) = 1.7
$calc(5 / 3,-1) = $int($calc(5 / 3)) = 1