DSL EXPRESSION:
$y += $x + 3


AST:
"block" [tt:block] [nt:StatementBlock]
    "+=" [tt:op_plus_equals] [nt:CompoundAssignment]
        "$y" [tt:field_name] [nt:DirectFieldValue]
        "+=" [tt:op_plus_equals] [nt:op_plus_equals]
        "+" [tt:op_plus] [nt:Operator]
            "$x" [tt:field_name] [nt:DirectFieldValue]
            "3" [tt:int_literal] [nt:int_literal]

