The Xo book

The tour shows the language in twelve short steps. The book goes deeper on the parts that make Xo different, one topic per chapter. Every program in a chapter is checked, run, and tested with the current toolchain before the site is published, and the output shown is what it printed.

1. Effects and capabilities: what a signature says a function can reach, and how to hand out less.
2. Error handling: errors as values, from chains, the ?? forms, and when a bug is a fault instead.
3. Concurrency (planned): tasks, channels, scopes, and isolation.
4. HTTP services (planned): handlers, routing, and a service built from the standard library.
5. Testing with fakes (planned): the fake Os, virtual time, and tests that never touch the network.
6. Modules (planned): xo.mod, editions, dependencies, and publishing.
7. Deploying (planned): cross compiling and shipping one binary.

For the API of every standard module, see the std reference.

1. Effects and capabilities: A signature lists what a function can reach, a capability value is the permission to reach it, and a narrowed capability is a smaller permission.
2. Error handling: Errors are values: chain them with from, handle them with ?? and match, and keep faults for bugs.