DSL EXPRESSION:
$y -=  $x


AST:
"block" [tt:block] [nt:StatementBlock]
    "-=" [tt:op_minus_equals] [nt:CompoundAssignment]
        "$y" [tt:field_name] [nt:DirectFieldValue]
        "-=" [tt:op_minus_equals] [nt:op_minus_equals]
        "$x" [tt:field_name] [nt:DirectFieldValue]

