LALRPop

LALRPop is a parser generator framework. Despite its name, it does not implement the LALR(1) algorithm, but rather LR(1). In fact, it has grand ambitions of eventually supporting all manner of parser generation algorithms (including more general variants like LL(*), GLR, etc), but those may or may not ever come to fruitition. :)

LALRPop has usability as a primary goal. You should be able to write compact, DRY, readable grammars. You shouldn't have to stress about writing action code or types if you don't want to. To this end, LALRPop has a number of nifty features:

1. Macros that let you extract common parts of your grammar. This means you can go beyond simple repetition like Id* and define things like Comma<Id> for a comma-separated list of identifiers.
2. Macros can also create subsets, so that you easily do something like Expr<"all"> to represent the full range of expressions, but Expr<"if"> to represent the subset of expressions that can appear in an if expression.
3. Compact defaults so that you can avoid writing action code much of the time.
4. Type inference so you can often omit the types of nonterminals etc.

To be clear, LALRPop is still early days. It's kind of spare time project. But it's coming along pretty quickly, now that a lot of the tricky stuff is out of the way. I'll update this README more with better instructions soon.

Instructions for use

LALRPOP integrates with cargo to preprocess files with the extension lalrpop. It will convert foo.lalrpop into foo.rs before your project builds. This will be a valid Rust module with one parse_XXX function per public symbol. For now, the documentation is spare; the best models to use are the test files in lalrpop-test.

To enable LALRPOP, add the following lines to your Cargo.toml:

[package]
...
build = "build.rs" # LALRPOP preprocessing

# Add a dependency on the LALRPOP runtime library:
[dependencies.lalrpop-util]
version = "0.4.0"

[build-dependencies.lalrpop]
version = "0.4.0"

And create a build.rs file that looks like:

extern crate lalrpop;

fn main() {
    lalrpop::process_root().unwrap();
}

(If you already have a build.rs file, you should be able to just call process_root in addition to whatever else that file is doing.)

That's it!