add `parse-tree`

brag/brag/codegen/codegen.rkt

@@ -152,7 +152,14 @@
                                       (parameterize ([current-source source])
                                         (parse tokenizer))])))]))
              
-             (define parse (make-rule-parser start-id))))))]))
+             (define parse (make-rule-parser start-id))
+             (provide parse-tree)
+             (define (parse-tree x)
+               (let loop ([x (syntax->datum (parse x))])
+                 (cond
+                   [(list? x) (map loop x)]
+                   [(char? x) (format "~a" x)]
+                   [else x])))))))]))
 
 
 ;; Given a flattened rule, returns a syntax for the code that