DSL EXPRESSION:
begin{@x=1;@y=2;} $z=3


AST:
* statement block
    * begin block
        * statement block
            * assignment "="
                * direct oosvar value "x"
                * int literal "1"
            * assignment "="
                * direct oosvar value "y"
                * int literal "2"
    * assignment "="
        * direct field value "z"
        * int literal "3"

