DSL EXPRESSION:
$x = (NF + NR) * 7; $y = OFS . $y . "hello"


AST:
* statement block
    * assignment "="
        * direct field value "x"
        * operator "*"
            * operator "+"
                * context variable "NF"
                * context variable "NR"
            * int literal "7"
    * assignment "="
        * direct field value "y"
        * dot operator "."
            * dot operator "."
                * context variable "OFS"
                * direct field value "y"
            * string literal "hello"

