$ ./expression_evaluator.pl
a:=1*(2+(3/5+2))
RPN: a 1 2 3 5 / 2 + + * :=  (a set to <4.6>)  ====> 4.6
Variables: a:4.6
b:=a+15
RPN: b a 15 + :=  (b set to <19.6>)  ====> 19.6
Variables: a:4.6, b:19.6
c:=(b-a)*(5+3+(9-6)*3)
RPN: c b a - 5 3 + 9 6 - 3 * + * :=  (c set to <255>)  ====> 255
Variables: a:4.6, b:19.6, c:255