# 29-haskell-foldmap-summary

This example shows intermediate Haskell aggregation with `foldMap` and monoids.

It includes:

- a structured deployment event type,
- a summary type built from monoidal fields,
- one `foldMap` pass that aggregates several useful metrics, and
- a test suite run by `nix flake check`.

Useful commands:

```bash
nix develop
cabal run
cabal run -- api:production:succeeded:3:platform,security worker:staging:failed-db-lock:1:ops ui:production:cancelled:2:frontend
cabal test

nix build
./result/bin/mini-summary api:production:succeeded:3:platform,security worker:staging:failed-db-lock:1:ops ui:production:cancelled:2:frontend

nix run . -- api:production:succeeded:3:platform,security worker:staging:failed-db-lock:1:ops ui:production:cancelled:2:frontend
nix flake check
```