# Dev Shell versus shellFor

This note covers `19-devshell-vs-shellfor/`, which builds one local package and exposes two dev shells around it.

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## 1. What Is Being Compared

The example defines:

- `devShells.<system>.generic`, built with `pkgs.mkShell`, and
- `devShells.<system>.shellFor`, built with `haskellPackages.shellFor`.

Both shells support the same local package, but they are assembled differently.

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## 2. Why the Difference Matters

`mkShell` is generic. You list tools directly.

`shellFor` is package-set-aware. It starts from Haskell packages and builds a shell around their dependencies.

That makes `shellFor` more tightly coupled to the package graph, while `mkShell` stays more explicit and general-purpose.

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## 3. Commands to Try

```bash
cd 19-devshell-vs-shellfor

nix develop .#generic
nix develop .#shellFor

nix build
./result/bin/mini-shell-choice

nix flake check
```