Thread

1. le-mark · 1790425610 · focus · HN ↗

   “Org” in this context is emacs org mode. Seems odd in this day and age that anyone would see hierarchical text format and think “regex”!

   1. cbarrick · 1790429171 · focus · HN ↗

      Indeed. Regexes are _regular_, which is non hierarchical by definition.

      The two are useful for different layers of abstraction: regex is for lexing and PEG is for parsing.

      Speaking of the Chomsky hierarchy, last I checked, it is still unproven whether or not PEGs can parse all context free languages. Intuitively, they're _probably_ weaker than CFGs, but no one has yet provided a counter example.

      1. sparkie · 1790439318 · focus · HN ↗

         PEGs aren't contained within the context-free languages, so it's not really intuitive that they're weaker, particularly as nobody has yet come up with a context-free language that a PEG cannot parse. They're capable of parsing things context-free grammars cannot.

         1. earleybird · 1790461132 · focus · HN ↗

            Ordered choice may cause a PEG parser to fail where a CFG parser would recognize the string.

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