DSL EXPRESSION:
NR == 3 { @u[2] = @v }


AST:
* statement block
    * cond block
        * operator "=="
            * context variable "NR"
            * int literal "3"
        * statement block
            * assignment "="
                * array or map index access "[]"
                    * direct oosvar value "u"
                    * int literal "2"
                * direct oosvar value "v"

