11–20 of 89 posts
I get really annoyed when people still complain about YACC while ignoring the four decades of practical improvement that Bison has given us if you bother to configure it.
https://pypi.org/project/pybison/ , or its predecessors such as https://pypi.org/project/ply/ ?
But yes, the decidedly non-traditional https://github.com/pyparsing/pyparsing/ is certainly more popular.
I wonder who it is that likes other kinds of parser. Over the last ~10 years or so I've read several articles arguing that recursive descent parsers are in fact great on HN. And they seem to be both the easiest to get started with and what almost all production-grade systems use. I've seen very little in the way of anything arguing for any other approaches.
LR however is more powerful, though this mostly matters if you don't have access to automatic grammar rewriting for your LL. More significantly, however, there's probably more good tooling for LR (or perhaps: you can assume that if tooling exists, it is good at what it is designed for); one problem with LL being so "simple" is that there's a lot of bad tooling out there.
The important things are 1. that you meaningfully eliminate ambiguities (which is easy to enforce for LR and doable for LL if your tooling is good), and 2. that you keep linear time complexity. Any parser other than LL/LR should be rejected because it fails at least one of these, and often both.
Within the LL and LR families there are actually quite a few members. SLR(1) is strong enough to be interesting but too weak for anything I would call a "language". LALR(1) is probably fine; I have never encountered a useful language that must resort to LR(1) (though note that modern tooling can do an optimistic fallback, avoiding the massive blowups of ancient LR tools). SLL(1) I'm not personally familiar with. X(k), where X is one of {SLL, LL, SLR, LALR, LR} and where k > 1, are not very useful; k=1 suffices. LL(*) however should be avoided due to backtracking, but in some cases consider if you can parsing token trees first (this is currently poorly represented in the literature; you want to be doing some form of this for error recovery anyway - automated error recovery is a useless lie) and/or defer the partial ambiguity until the AST is built (often better for error messages anyway, independent of using token trees).
I wonder who it is that likes other kinds of parser. Over the last ~10 years or so I've read several articles arguing that recursive descent parsers are in fact great on HN. And they seem to be both the easiest to get started with and what almost all production-grade systems use. I've seen very little in the way of anything arguing for any other approaches.
But remember that the articles arguing for recursive descent parsers are arguing against the long-dominant paradigm of using LR parsers. Plenty of us still like LR parser generators (see my other comment.) In between "easiest to get started with" and "what production-grade systems use", there is "easy to actually finish a medium-sized project with." I think LR parsers still defend that middle ground pretty well.
That was part of my question I think. I wouldn't have been able to tell you that the dominant paradigm being argued against was LR parsers, because I've never come across even one that I'm aware of (I've heard of them, but that's about it). Perhaps it's academia where they're popular?
A middle ground that I think is sometimes useful is to use an LR parser generator to check if the grammar is ambiguous, but use recursive descent for the actual implementation. Since we won't actually use any code from the LR parser generator, you can pick whatever one you prefer regardless of the programming language.
I wonder who it is that likes other kinds of parser. Over the last ~10 years or so I've read several articles arguing that recursive descent parsers are in fact great on HN. And they seem to be both the easiest to get started with and what almost all production-grade systems use. I've seen very little in the way of anything arguing for any other approaches.
Earlier quoted context omitted.
But remember that the articles arguing for recursive descent parsers are arguing against the long-dominant paradigm of using LR parsers. Plenty of us still like LR parser generators (see my other comment.) In between "easiest to get started with" and "what production-grade systems use", there is "easy to actually finish a medium-sized project with." I think LR parsers still defend that middle ground pretty well.
> But remember that the articles arguing for recursive descent parsers are arguing against the long-dominant paradigm of using LR parsers That was part of my question I think. I wouldn't have been able to tell you that the dominant paradigm being argued against was LR parsers, because I've never come across even one that I'm aware of (I've heard of them, but that's about it). Perhaps it's academia where they're popul…
I wonder who it is that likes other kinds of parser. Over the last ~10 years or so I've read several articles arguing that recursive descent parsers are in fact great on HN. And they seem to be both the easiest to get started with and what almost all production-grade systems use. I've seen very little in the way of anything arguing for any other approaches.
It seems to be mainly academics and others interested in parsing theory, and those who like complexity for the sake of complexity.