substitute with recursive regexps?

[hexcoder]

When I read about JavaFans recursive regexps, I found it immediately fascinating. Then I realized all examples use the regexp to match something. No example showed how to use it in a substitution.

I wonder if it is possible to do transformations on a string based on a named recursive capture.

For example given

my $pat = qr {
 (?(DEFINE) (?<number> (?: [0-9]+ ))
 (?<sign> (?: [-+] ))
 (?<expr> (?: (?&term) (?: \s* [-+] \s* (?&expr))? ))
 (?<term> (?: (?&factor) (?: \s* [/*] \s* (?&term))? ))
 (?<factor> (?: (?&number) |
                (?&sign) \s* (?&factor) |
               \( \s* (?&expr) \s* \)))
 )
 (?&expr) }x;

how do you change all (?&expr) to something like Expression($+{expr})?

A suitable string could be '1+2*3' and the expected result would be Expression(Expression(1)+Expression(Expression(2)*Expression(3))).

Also interesting: how to substitute a subexpression like (?&factor).

Thanks! hexcoder

Edit: fixed a typo in the replacement text

Edit2: Better wording in the second question.