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The unwritten corollary of course is that "almost nobody writes commercial compilers." :) Almost all of us do, however, write parsers for data, config files, languages etc... all the time. I'd personally used ANTLR of course for all my parsing needs beyond the trivial.

Does Pandoc count? IIRC it implements CommonMark in a PEG.

I don't understand the question. I am not familiar with Haskell but from what I understand Pandoc is a group of hand crafted parsers (readers) for markup formats.

How does this relate to a discussion on the relevance of parser generators / libraries?

https://github.com/jgm/pandoc/tree/master/src/Text/Pandoc

If you check the Parser.hs file there, Pandoc uses Parsec.

Yacc/bison seems pretty common for stuff implemented in C.