DSL EXPRESSION:
$i += 2


AST:
* statement block
    * assignment "="
        * direct field value "i"
        * operator "+"
            * direct field value "i"
            * int literal "2"

a   b   i x          y
pan pan 3 0.34679014 0.72680286
eks pan 4 0.75867996 0.52215111
wye wye 5 0.20460331 0.33831853
eks wye 6 0.38139939 0.13418874
