nix-playgraound/notes/022-devshell-vs-shellfor.md

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

cd 19-devshell-vs-shellfor

nix develop .#generic
nix develop .#shellFor

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

nix flake check