Add support for semantic action for language parser

[stevefan1999-personal]

I was trying to do inline type inference rather than to generate a parse tree then traverse it after PEG passes, this way we could avoid some potential backtracking issue by stopping ahead and hence sped up (or terminate) the parsing process.

I know Clang does parse tree scan too but they clearly had more information than what mpc currently have to deduce a sound combinations.

[orangeduck]

If you build up your own AST data type as you go using the combinator approach (rather than the grammar approach) you can insert as much functionality as you like in-between parsing. Yes it is a bit less user friendly than the grammar definition but it is the only sane way to do this sort of thing while still making use of mpc.