CGI::Ex::Template does all of this.

You can add arbitrary entries to the $OPERATORS table and then use the built in functions to rebuild the global qr's helping in the parsing.

The parse_expr method takes a reference to a string (which it will consume) and returns a parsed optree.

The play_expr method takes the optree and actually executes it.

The parser allows for TT2 style nested variables, function calls, number, double and single quoted strings, arrays and hashes. It also has proper precedence and associativity parsing.

The entry in the $OPERATORS table should contain the following:

   type: prefix, postfix, left, right, none, ternary, or assign (right
+)
   precedence: the relative precedence value
   symbols or names: an arrayref of symbols or operators for that oper
+ation
   function: a code ref to run when that operator is found.
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It isn't entirely general as the variable names are TT2'ish - but it certainly could be used in other applications.