Doug followed up on one of our groff threads over on the TUHS list. Here it is.
At 2024-02-17T17:52:11-0500, Douglas McIlroy wrote: > To expand on Branden's observation that translating from one member of the > roff family to another is hard, I note that the final output usually > presents a text in a shape that has been fine-tuned for appearance. In > grammatic terms it might best be presented in transformational terms a la > Chomsky: a basic text with a fairly simple grammar tweaked by > pretty-printing transforms. > > Translation involves parsing input into an AST according to one grammar and > unparsing to generate output according to another. Chomsky's work uses > transformational grammars primarily for generation. I'm not aware of any > implementation of the inverse: parsing according to a transformational > grammar. Certainly no practical tools exist for doing so. > > Unfortunately, one doesn't consciously write roff according to the model I > have outlined. This means that parsing it is more like parsing a natural > language than a strictly defined programming language. So, the absence of > formal tools is exacerbated. Roff scripts, like everyday English, are > written according to an intuitive--and occasionally ad hoc--grammar that > varies both with authors and with time. And seventy years of hard work has > not yet fully automated the parsing of English. > > Doug
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