# [Bld](https://github.com/rife2/rife2/wiki/What-Is-Bld) extension to generate ANTLR4 parsers

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A `bld` extension for generating Java sources from ANTLR4 parsers.

The complete document of `Antrl4Operation` can be found in its [javadocs](https://rife2.github.io/bld-antlr4/rife/bld/extension/Antlr4Operation.html).

This is an example usage where your ANTLR4 sources would be located at
`src/main/antlr` and the parsers generated into `build/generated`. The `compile`
command then uses an adapted `CompileOperation` to include the generated
sources into the main source directories.

```java
private final Antlr4Operation antlr4Operation_ = new Antlr4Operation();

@BuildCommand(summary = "Generates the grammar Java sources")
public void generateGrammar()
throws Exception {
    antlr4Operation_.executeOnce(o -> o
        .sourceDirectories(List.of(new File(srcMainDirectory(), "antlr")))
        .outputDirectory(new File(buildDirectory(), "generated"))
        // these options are specific to ANTLR4, please refer to the extension
        // documentation to learn more about these and other option
        .visitor()
        .longMessages());
}

@BuildCommand
public void compile()
throws Exception {
    // always generate the latest grammar before compiling the sources
    generateGrammar();

    // compileOperation_ is part of the main project, include the generated
    // grammar with the main sources
    compileOperation_.executeOnce(o -> o
        .fromProject(this)
        .mainSourceDirectories(List.of(antlr4Operation_.outputDirectory())));
}
```