generating_parsers_automatically.md

Generating Parsers Automatically

Sometimes, we may want to generate parsers while running our program (i.e., cargo run). In this case, we can use rustemo-compiler (i.e., the library of rcomp) in the build script of Cargo.

First, we have to add rustemo-compiler to the build dependencies.

cargo add --build rustemo-compiler

The build-dependencies in Cargo.toml should look like this:

[build-dependencies]
rustemo-compiler = "0.6.0"

Next, we create the build script, build.rs:

fn main() {
    rustemo_compiler::Settings::new().process_dir().unwrap();
}

For more information about the settings, please refer to rustemo_compiler::Settings. Note that build.rs is put in the project root directory, sharing the same parent as src folder's.

Assume our grammar is called my_grammar.rustemo and is put in the folder src. Previously, we use rcomp to generate parsers and include them in main.rs like this:

mod my_grammar;
mod my_grammar_actions;

Now, we remove the two lines and include the auto-generated parsers in the following way:

rustemo::rustemo_mod!(my_grammar, "/src");
rustemo::rustemo_mod!(my_grammar_actions, "/src");

The parsers will be generated automatically when we run cargo run.

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