Hello, Volt

Save this as hello.volt:

use std::io;

fn main() -> void {
    val name = "Volt";
    std::println("Hello, {}!", name);
}
// expect: Hello, Volt!

and run it:

voltc run hello.volt

use std::io; makes std::io’s functions reachable as std::name, so std::println is std::io::println. The format string is checked while compiling: each {} takes one argument, and passing too few or too many is an error.

voltc build hello.volt -o hello makes an executable instead; voltc check hello.volt only type checks. Every file on the command line is part of one program: voltc run main.volt util.volt.

For anything bigger, let bolt manage the build:

bolt new hello
cd hello
bolt run

hello/
├── .gitignore         /target (bolt new starts a git repository, unless it's inside one)
├── bolt.toml          the manifest: name, version, dependencies, features
└── src/
    └── main.volt      the program (every .volt file under src/ is part of it)

bolt build --release builds optimized, bolt test runs the package’s test blocks and each program in tests/, and bolt add adds dependencies. The bolt section covers all of it.

main returns void, an integer (the exit code), or an error union like !void: an error that reaches the end of main prints its name and exits with 1.

use std::io;

error config_error { MISSING }

fn load() -> config_error!i32 {
    return config_error::MISSING;
}

fn main() -> !void {
    val n = try load();   // the error leaves main: it prints and the exit code is 1
    std::println("{}", n);
}

Next: a tour of the language.