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Comment by carsongross | Hacker News Reader

I really didn't understand grammars until I started doing hand-rolled top-down recursive descent parsing for Gosu.

It's a shame that parsing in CS schools is taught using theory and lex/yacc type tools when a basic lexer and recursive descent parser can be written from first principles in a few months. It is more incremental, and it gives you a much deeper feel for the concepts, plus it lets you learn a bit about software engineering and organization as well.

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Parsing and compilers are an area where I think "the theory gets in the way"; I started by reading the Dragon Book, and while I (vaguely) understood what it was talking about, the feeling it gave was "parsers are complex, use a parser generator instead"... which sounds like a good idea until you actually try to debug one. I eventually realised that recursive descent was much simpler, and with things like the "Let's Build a Compiler" articles everything became so clear and it felt like all that theory I learned before was mostly useless. I think the fact that top-down parsers are theoretically less powerful doesn't make much difference in practice; and the trend of compilers (in C at least) now seems to be to move away from generated parsers and to recursive descent.

Big, "production quality" compilers like GCC and LLVM use RD, and so do small ones like (o)tcc and various others' "toy compiler" projects (e.g. https://news.ycombinator.com/item?id=8558822 and https://news.ycombinator.com/item?id=8576068) The "precedence climbing" method (http://www.engr.mun.ca/~theo/Misc/exp_parsing.htm ), which simplifies and makes RD more efficient, is common too but I don't think I've seen it appear in any of the usual academic texts.

Funny enough, I found the dragon book way too applied and not theoretical enough. Perhaps it was just a different feeling about the same problem: the dragon book is just not very good anymore.

Something like Parsec seems like a good introduction into writing your own parsers. You can figure out formal grammars later.

It is a shame that Gosu has not become more popular as a JVM language. You guys were doing things that took other languages years to catch up.

Yep, them's the breaks...

We are still working on it and it has a long life ahead of it, since it is crucial to many very large, un-sexy companies.

Indeed. Also Groovy++ (aka Groovy with static typing) is worth mentioning.

Or even Beanshell. In fact, the ideas behind Beanshell (i.e. closures on the JVM) and Groovy++ (i.e. static typing) were scooped up and copied into Groovy, that kitchen sink language, which was bundled as part of Grails, that knock-off of Rails for the JVM.

The software industry is divided into "Makers" and "Takers". The people behind Gosu are obviously Makers, whereas those presently behind Groovy are Takers.

> "...copied into Groovy, that kitchen sink language, which was bundled as part of Grails, that knock-off of Rails for the JVM. The software industry is divided into 'Makers' and 'Takers'. The people behind Gosu are obviously Makers, whereas those presently behind Groovy are Takers."

This is all wrong. Groovy predates Grails, as Grails was written in Groovy. Gosu and Groovy came out at roughly the same time, and IIRC, Groovy had closures and features like the Elvis operator before Gosu did.

You apparently don't like Groovy's current owners, but slamming Groovy for implementing static typing and qualifying them as takers for doing so makes no sense at all.

I've gotten the impression over the years that Grails is written in Java and only bundles Groovy for user scripting, but I haven't checked up recently. I certainly looked through the Gradle codebase when its version 2.0 came out and there was hardly a line of Groovy code in there, only Java. It, too, only uses Groovy for user scripting. If I'm right about the Grails codebase, static-typed Groovy isn't actually used to build any systems of note. Perhaps Cedric Champeau, who wrote the static-typed Groovy codebase, will use it to build the Groovy for Android he's presently working on. It'll be interesting to see whether he uses it or uses Java because it'll show whether he has enough faith in what he built to actually use it to build something with it. Until static-typed Groovy is used to build something, Groovy will remain a dynamically-typed scripting language for testing, Gradle builds, webpages, etc.

I'm a sophomore at Ohio State and context free grammars are actually a major topic in one of our early software courses. We also got to write a recursive decent parser for a very simple made up language as one of our projects. Really exciting curriculum over here.

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