DSL EXPRESSION:
$y <<= $x


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

