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Megaparsec Tutorial

markkarpov.com

52 pointsswatson7419 comments

Starting with Megaparsec can be a little intimidating. I always encourage new users to start with the built-in ReadP instead. I even wrote an appreciated beginner tutorial on ReadP and parser combinators more generally: https://two-wrongs.com/parser-combinators-parsing-for-haskel...

Thanks for sharing. I've used megaparsec a little but never looked at ReadP. Your tutorial is concise and helpful, I'd have ended up with better intuition faster if I started there.

I happened write a parser for a binary protocol using attoparsec before ever trying megaparsec and I found it to be a nice stepping stone.

attoparsec is a nice, tight library. It's a true classic.

what considerations are the between choosing parser combinators and using a parser generator?

The generator requires that you specify a grammar; combinators don’t.

Because the generator has your grammar, it can analyze it and tell you if it’s ambiguous. Combinators can’t.

Combinators easily support arbitrary lookahead.

The combinator libraries I’ve seen in Haskell can provide excellent error messages while parsing, especially if you spend time tweaking them. The generators I’ve seen don’t have error messages as good.

Typically with a generator you use a separate lexer, though I suppose you don’t have to. With combinators, you can use a separate lexer, but this is not typical.

Generators require you to run a separate tool to generate the parser and maybe the lexer as well. With combinators you just write them in the host language. This impacts your debugging experience.

Combinators are great for little ad-hoc parsers but if you have gotten to the point of laying out a formal grammar you should go with a parser generator.

I thought this was going to be an article about measuring vast distances in space. Instead it's a tutorial abouta Haskell library. Personally, I was disappointed.

Excellent. Similar. Now I want to write an article about Galaxy Clusters and the nigh incomprehensible space between them. You are here -> . You are tiny.

[1] https://en.wikipedia.org/wiki/Galaxy_cluster

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