# 09-haskell-newtype

This example shows intermediate Haskell domain modeling with `newtype` and smart constructors.

It includes:

- `newtype` wrappers for `UserName` and `Email`,
- smart constructors that validate raw input,
- an explicit `Either String` error path, and
- a test suite run by `nix flake check`.

Useful commands:

```bash
nix develop
cabal run
cabal run -- learner learner@example.com
cabal test

nix build
./result/bin/mini-registration learner learner@example.com

nix run . -- learner learner@example.com
nix flake check
```