avoid weird side effects by cloning the parsers that assembly macro p…

…atterns

src/Macro.php

@@ -573,7 +573,7 @@ private function layer(string $start, string $end, Parser $parser) : Parser {
             )
             ->onCommit(function(Ast $result) use($parser) {
                 $id = $this->lookupCapture($result->label);
-                $this->parsers[] = $parser->as($id);
+                $this->parsers[] = (clone $parser)->as($id);
             });
     }