nix-make | Experimental Nix build management stuff

There are a number of things about your example.

First off, you use auto with Spirit Qi expressions. That's not valid, and leads to UB:

• Assigning parsers to auto variables
• also boost spirit qi parser failed in release and pass in debug
• undefined behaviour somewhere in boost::spirit::qi::phrase_parse
• boost spirit V2 qi bug associated with optimization level

Next off, you chose to use polymorphic Ast nodes. That's possible but likely not efficient:

• How can I use polymorphic attributes with boost::spirit::qi parsers?
• Semantic actions runs multiple times in boost::spirit parsing
• but also making a vector of shared pointers from Spirit Qi which you may have found

Finally, there's the left recursion, since your expression starts with itself, leading to infinite recursion. The only way to solve it is to split your productions up into "levels" of expressions. This also aids in generating the desired operator precedence: