0. Pack your compiler

From the repository root:

nix develop
bend guide
bend src/01-values.bend

If Nix complains that flake.nix is untracked, follow the development-environment instructions in the workspace README. Do not silently switch to an old Bend 1 installation: Bend 1/HVM syntax is not this language.

Useful companions:

bend --help
bend base --types
bend base List
bend base Nat

This tutorial follows the upstream Bend 2 guide consulted on 2026-10-17. Bend is evolving quickly; your installed compiler's bend guide and bend base are the authority if a syntax or library detail differs.

Two sorts of main

A pure main can return a value:

import Base

def main() -> U32:
  42

bend file.bend checks it, normalizes its result, and prints the value. This is handy for tiny experiments, but normalization is not a performance benchmark.

A main returning IO(Unit) runs effects, such as printing, through the compiled runtime. We meet that version in chapter 7.

Haskell companion: GHC's executable entry point has type IO (). To explore pure Haskell expressions, you normally use GHCi. Bend's command also evaluates a pure main, so our early programs need no printing ceremony.

The compiler may print checking information alongside the result. When a chapter says “expect 42”, it means the program's value, not an exact transcript of every compiler message.