# 37-haskell-transformer-stack

This example shows intermediate Haskell effect composition with a transformer stack.

It includes:

- a rollout environment carried by `ReaderT`,
- explicit rollout failures carried by `ExceptT`,
- ordered audit lines carried by `Writer`,
- one stacked workflow that validates and renders a rollout summary, and
- a test suite run by `nix flake check`.

Useful commands:

```bash
nix develop
cabal run
cabal run -- api:production:4
cabal test

nix build
./result/bin/mini-stack api:production:4

nix run . -- api:production:4
nix flake check
```