# 28-haskell-applicative-validation

This example shows intermediate Haskell validation with an Applicative error accumulator.

It includes:

- a custom `Validation` type that accumulates multiple errors,
- a release manifest built from validated fields,
- a CLI that reports all invalid fields at once, and
- a test suite run by `nix flake check`.

Useful commands:

```bash
nix develop
cabal run
cabal run -- service=api-gateway env=production owners=platform,security replicas=3 strategy=canary:20 window=22-24
cabal test

nix build
./result/bin/mini-validation service=api-gateway env=production owners=platform,security replicas=3 strategy=canary:20 window=22-24

nix run . -- service=api-gateway env=production owners=platform,security replicas=3 strategy=canary:20 window=22-24
nix flake check
```