One if per statement
I reduced the number of "ifs line_like" to only one per statement (except for variable declarations because I'm tired (? ), using more generic model lines like IF $condition THEN, JOIN $expression AND $expression IN $str-var and ADD $num-expr AND $num-expr IN $num-var.
I think this makes the code more readeable and maintainable, way less error-prone, and it makes it easier to add statements.
As far as I know I tested each statement (and its possibles argument combinations) and they work, and all the repo examples as well. But since is a pretty big PR I think it needs a review.