Updates to ExprTk

Author: ArashPartow

bench_expr_weird.txt

@@ -99,4 +99,12 @@ a^-b
 -1.1*a^(+b-0)
 -1.1*a^-b
 -b^2^3-b^6
--(-b^2^3)+b^6
+-(-b^2^3)+b^6
+(-1)^0
+(-1)^1-1
+(-1)^(1-1)
+(-1)^(a-a)
+-1^0
+-1^1-1
+-1^(1-1)
+-1^(a-a)

exprtk/exprtk.hpp

@@ -35362,7 +35362,7 @@ namespace exprtk
                                             const bool collect_variables,
                                             const bool collect_functions,
                                             const bool vector_pass,
-                                            symbol_table_t& ext_symbol_table = symbol_table_t())
+                                            symbol_table_t& ext_symbol_table)
          {
             symbol_table_t symbol_table;
             expression_t   expression;