Create and run a project

A single .b file is fine for a quick test. A real program is a project: a folder tree with a manifest at its root. This page shows how one is laid out and how to run it.

What makes a project

A module is a directory tree with a file named beans.pot at its root. That file is the manifest. It names your module. (The name POT is a pun; see Why it is called POT.)

The smallest manifest just names the module:

module shop

Create it from the project directory with:

beansc pot init shop

This command refuses to overwrite an existing beans.pot.

The main package

An application’s root package is package main, and it needs an fn main(), the entry point. A minimal project looks like this:

myapp/
  beans.pot
  main.b

beans.pot:

module myapp

main.b:

package main

import std.io

fn main() {
    io.println("hello from myapp")
}

One folder is one package

The rule is simple: one folder = one package. Every .b file in a folder shares that package. Files in the same folder do not import each other; they already see each other’s names.

So you can split main across files:

myapp/
  beans.pot
  main.b       package main
  helpers.b    package main   (same package, no import needed)

Sub-folders are sub-packages

A sub-folder is a separate, importable package. If you have:

shop/
  beans.pot
  main.b
  money/
    money.b    package money

then main.b imports the sub-package by its path and uses it by its name:

package main

import shop.money

fn main() {
    let m: money.Money = new money.Money(19.99)
}

The import path is shop.money. Inside code you use it as money.thing, because the package calls itself money in its package clause.

Running a project

Point beansc run at the file with fn main(). For the bundled multi-package example:

beansc run examples/shop/main.b

beansc finds the beans.pot above that file, resolves every package in the module, and runs it.

Single-file mode

Without a beans.pot, a lone .b file runs in single-file mode. Standard library imports (std.io) and Git imports still work. Local packages do not, because there is no module for them to belong to. As soon as you want more than one package, add a beans.pot.

For every manifest field, see the beans.pot manifest. For a full three-package project walked through end to end, see the shop example.