3 ms·

Why would you say that? Yacc and other parser generators exist for a good reason: hand written parsers can be quite hairy to debug and extend, while parser gene

by p4bl0 5y ago

Why would you say that? Yacc and other parser generators exist for a good reason: hand written parsers can be quite hairy to debug and extend, while parser generators offer a domain specific language to specify your grammar and can generate efficient parser code based on it. What are the arguments in favor of manually writing parsers?

codr7 5y ago
What few seem to realize is that it's perfectly possible to abstract out some of the work and create an extensible foundation for manual parsers. Since it's all regular code, you can use the full power of the host language to deal with the problem. https://github.com/codr7/swifties/blob/main/Sources/Swifties/Parser.swift https://github.com/codr7/swifties/blob/main/Sources/Swifties...
- p4bl0 5y ago
  I understand that, but I still find it easier to write/maintain/extend a grammar than a parser for that grammar.
  - brundolf 5y ago
    If you've got the right utility functions, a handwritten parser visually maps very directly to its grammar. It won't be as concise of course, but cognitively you can work with it almost as if it were just a grammar.
chrisseaton 5y ago
Fundamentally I don't think parsing is a problem that's complex enough to warrant a custom tool and language. And even if it was Yacc is the wrong tool for the job in most cases. Since most languages are context-sensitive, you almost always have to bend Yacc, which is designed for context-free languages, out of shape to apply it. It's a hammer but we hardly have any nails, and the nails can just be pushed in by hand without a hammer, and they're the wrong type of nails anyway so that hammer isn't really compatible, and top of that it's a really expensive hammer.
- rightbyte 5y ago
  Isn't the context sensitivity handled when you build an AST with the action statements in Yacc?
  - chrisseaton 5y ago
    Yes - so straight away you have to leave the DSL and bypass the formal mode of Yacc. At which point why bother with it? If the first thing you need to do with your tool is hack around it, maybe the tool isn’t so well-designed? And actions often do things like side-effect changes to the lexer state, so it gets worse from there.

by p4bl0 5y ago

codr7 5y ago

What few seem to realize is that it's perfectly possible to abstract out some of the work and create an extensible foundation for manual parsers. Since it's all regular code, you can use the full power of the host language to deal with the problem. https://github.com/codr7/swifties/blob/main/Sources/Swifties/Parser.swift https://github.com/codr7/swifties/blob/main/Sources/Swifties...

p4bl0 5y ago
I understand that, but I still find it easier to write/maintain/extend a grammar than a parser for that grammar.
- brundolf 5y ago
  If you've got the right utility functions, a handwritten parser visually maps very directly to its grammar. It won't be as concise of course, but cognitively you can work with it almost as if it were just a grammar.

chrisseaton 5y ago

Fundamentally I don't think parsing is a problem that's complex enough to warrant a custom tool and language. And even if it was Yacc is the wrong tool for the job in most cases. Since most languages are context-sensitive, you almost always have to bend Yacc, which is designed for context-free languages, out of shape to apply it. It's a hammer but we hardly have any nails, and the nails can just be pushed in by hand without a hammer, and they're the wrong type of nails anyway so that hammer isn't really compatible, and top of that it's a really expensive hammer.

rightbyte 5y ago
Isn't the context sensitivity handled when you build an AST with the action statements in Yacc?
- chrisseaton 5y ago
  Yes - so straight away you have to leave the DSL and bypass the formal mode of Yacc. At which point why bother with it? If the first thing you need to do with your tool is hack around it, maybe the tool isn’t so well-designed? And actions often do things like side-effect changes to the lexer state, so it gets worse from there.