Participle: A parser library for Go

https://github.com/alecthomas/participle

by pjf • 8 years ago

128 26 8 years ago

github.com

kjeetgill• 8 years ago

Parsers are one of those fields I wish I had the time to really study deeply. I'm especially impressed with LALRPOP.

Cribbed from a previous comment of mine:

From time to time I find myself revisiting this thread: "Writing parsers like it is 2017"[0].

In particular I love a Rust parser generator called LALRPOP and it's emphasis on diagnosing ambiguous grammars [1].

What I’ve tried to do now in LALRPOP is to do that clever thinking for you, and instead present the error message in terms of your grammar. Perhaps even more importantly, I’ve also tried to identify common beginner problems and suggest solutions.

They work out a fairly deep example with error guidance in ambiguous grammars in that post.

[0] https://news.ycombinator.com/item?id=15016061

[1] http://smallcultfollowing.com/babysteps/blog/2016/03/02/nice...

pjmlp• 8 years ago

Clever idea of using struct tags for grammar rules.

laumars6• 8 years ago

Wouldn't that then require reflection, which is "slow" (comparatively speaking - if this isn't in a hot path then perhaps who cares?)

bpicolo• 8 years ago

It's not in the hot path, it's used to generate the parser.

childintime• 8 years ago

This maps well to how I think of parsing. Refreshing. I will have to give it a shot.

weberc24• 8 years ago

This looks really cool. I spent a few weeks last year trying to build my first programming language, but I kept getting bogged down by parsing and eventually gave up.

laumars6• 8 years ago

Parsing isn't actually that hard once you wrap your hard around the problem. There are lots of good guides for writing parsers online which really helped me out when I was feeling the same bourdon as you are.

So what I'm trying to say is stick with it and I'm sure you'll crack it. :)

azhenley• 8 years ago

Definitely. I used to always get stuck on the parsing part, and it definitely is time consuming to get right, but once you get past it once it is much easier to tackle in the future.

Then you realize that parsing is only a small piece of making your own language!

weberc24• 8 years ago

How do you write a parser in a language like Go? I stumbled upon parser combinatory and tried to shoehorn them into Go, but the lack of generics mostly prohibited this. I also tried imperatively writing the parser, but this was tedious and error prone. I also explored parser generators, but these seemed to have huge learning curves and still produced awful code. Beyond that, it’s hard to tell what kind of parser I need because of all of the academic jargon. :/

I would love to be pointed in the right direction!

cweagans2• 8 years ago

You should check out Thorsten Ball's interpreterbook.com and compilerbook.com. I went through the former - it's amazing. I'm eagerly awaiting the release of the latter.

It walks through the creation of an entire interpreter from scratch using just core Go packages, including test coverage.

weberc24• 8 years ago

I'll do that, thanks for the tip! I heard about the interpreter book from the GoTime podcast, but didn't know about the compiler book. :)

pebers• 8 years ago

I've used this before - really nice library and an easy way of getting started without having to write so much custom code. Only down side is that of course it's still faster to hand-write a parser :)

iampims• 8 years ago

A good intro by Rib Pike for those who’d like to learn more about parsers/lexers https://youtube.com/watch?v=HxaD_trXwRE

deklerk• 8 years ago

s/Rib/Rob :)

skybrian2• 8 years ago

Cool idea. The way it handles alternatives looks awkward since each alternative is a field in a struct. You have to check each field to find the one that's not nil.

(See Term in the example.)

Normally this would be done with an interface, like in go/ast

skybrian2• 8 years ago

Although, on second thought, this means writing a chain of if-else statements instead of a type switch in a visitor. Maybe it's not that big a difference?

Participle: A parser library for Go

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