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ABNF Parser Generator

Working with the Prioritized-Choice Rule

The following exercises demonstrate several cases of valid but problematic CGFs with discussion and prioritized-choice solutions. They are arranged from trivial to head-scratching and it is suggested that you try them in the order presented.

exercise 1 – longest alternative first
exercise 2 – repetitions
exercise 3 – non-trivial
exercise 4 – impossible (almost)

ABNF Grammar:   X

Input String:   X

Parser Output: