Nice. Being familiar with forth and thus reverse polnish notation, I use Math::RPN with ~/bin/rpn containing

#!/usr/bin/perl
use Math::RPN;$|=1;
1 while($_="@ARGV"||<>)&&!((@s=rpn@s,split)&&$s[-1]=~/^q/i||print("@s 
+")&&@ARGV&&print($/))
[download]

for ad-hoc calculations.