Obscure error when making a small mistake.

[heegaiximephoomeeghahyaiseekh]

   (defvar *dash/slash*
            " DASH-OR-SLASH = DASH SLASH
        DASH          = \"-\" 4DIGITS
        SLASH         = \"/\" 2DIGITS "
    "A grammar with a subtle error: DIGITS instead of DIGIT.")

    (parse-abnf-grammar *dash/slash* :dash-or-slash :registering-rules '(:dash :slash))

You end up getting an error about a failing DESTRUCTURING-BIND. WTF?

After extensive debugging, I found my way to abnf.lisp:522 (line number after adding several (declare (optimize (debug 3))) lines to different functions), which reads:

       (destructuring-bind (rule-name rule-definition)
           (or (assoc definition rule-set)
               (assoc definition *abnf-default-rules*))
         (let* ((already-expanded-rules
                 (cons definition already-expanded-rules))

Adding an error to the end of the or expression results in much easier debugging:

       (destructuring-bind (rule-name rule-definition)
           (or (assoc definition rule-set)
               (assoc definition *abnf-default-rules*)
               (error "Unknown rule: ~a" definition))
         (let* ((already-expanded-rules
                 (cons definition already-expanded-rules))

Then, when you give it the grammar at the top, you get the error "Unknown rule: ABNF-DIGITS." It would be better if someone would bother to remove the ABNF- prefix, but even with the prefix it's a marked improvement.

[dimitri]

The cl-abnf code hasn't seen many usage yet, so please consider improving it by sending pull requests if you're an interested user. Welcome to the project!