mirror of
https://github.com/simplex-chat/haskell.nix.git
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Yvan Sraka
28ed2a6dc2
* Fix #1558: add flake template for `nix flake init` This depends on https://github.com/NixOS/templates/pull/40 This issue makes both `nix run haskell-nix#hix -- init` and `nix flake init --template haskell-nix#template --impure` do the same thing! * Update getting-started-flakes.md
135 lines
3.7 KiB
Markdown
135 lines
3.7 KiB
Markdown
# Getting started with flakes
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This version of the getting started guide is for users who
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are using [Nix Flakes](https://nixos.wiki/wiki/Flakes).
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The non flakes version of the guide is [here](getting-started.md).
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`haskell.nix` can automatically translate your
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[Cabal](https://cabal.readthedocs.io/en/latest/cabal-project.html)
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or [Stack](https://docs.haskellstack.org/en/stable/README/#quick-start-guide)
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project and its dependencies into Nix code.
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Assuming you have [Nix](https://nixos.org/download.html) installed, you can
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start setting up your project.
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## Using `flake init` and `nix`
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The `flake init` command create an example `hello` package from hackage
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containing an `flake.nix` and `nix/hix.nix` file. The project can be used with
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regular `nix` tools.
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```bash
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nix flake init --template templates#haskell-nix --impure
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# `--impure` is required by `builtins.currentSystem`
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nix develop
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cabal build
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```
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To view the contents of the flake run:
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```
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nix flake show
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```
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To build a component with nix:
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```
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nix build .#hello:exe:hello
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```
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To build and run a component:
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```
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nix run .#hello:exe:hello
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```
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## Setting up the binary cache
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IMPORTANT: you *must* do this or you *will* build several copies of GHC!
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You can configure Nix to use our binary cache, which is pushed to by CI, so should contain the artifacts that you need.
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You need to add the following sections to `/etc/nix/nix.conf` or, if you are a trusted user, `~/.config/nix/nix.conf` (if you don't know what a "trusted user" is, you probably want to do the former).
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```
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trusted-public-keys = [...] hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ= [...]
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substituters = [...] https://cache.iog.io [...]
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```
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If you're running NixOS, you need to add/update the following in your `/etc/nixos/configuration.nix` files instead.
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```nix
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# Binary Cache for Haskell.nix
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nix.settings.trusted-public-keys = [
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"hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ="
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];
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nix.settings.substituters = [
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"https://cache.iog.io"
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];
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```
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NixOS-21.11 and older use slightly different settings.
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```nix
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# Binary Cache for Haskell.nix
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nix.binaryCachePublicKeys = [
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"hydra.iohk.io:f/Ea+s+dFdN+3Y/G+FDgSq+a5NEWhJGzdjvKNGv0/EQ="
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];
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nix.binaryCaches = [
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"https://cache.iog.io"
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];
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```
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This can be tricky to get setup properly. If you're still having trouble getting cache hits, consult the corresponding [troubleshooting section](../troubleshooting.md#why-am-i-building-ghc).
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## Scaffolding
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The following work with `stack.yaml` and `cabal.project` based
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projects.
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Add `flake.nix`:
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```nix
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{{#include getting-started-flakes/flake.nix}}
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```
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> **Note:** Git dependencies
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>
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> If you have git dependencies in your project, you'll need
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> to [calculate sha256 hashes for them](./source-repository-hashes.md).
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### Working with a project
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Top-level attributes are Haskell packages (incl. dependencies) part of your project.
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To build the library component of a package in the project run:
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```shell
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nix build .#your-package-name:lib:your-package-name
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```
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There are also other components such as `exe`, `test` and `benchmark`.
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To build an executable:
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```shell
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nix build .#your-package-name:exe:your-exe-name
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```
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To use the `devShell` provided by the flake run:
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```shell
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nix develop .
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cabal repl your-package-name:lib:your-package-name
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cabal build your-package-name
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```
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To open a shell for use with `stack` see [the following issue](https://github.com/input-output-hk/haskell.nix/issues/689#issuecomment-643832619).
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## Going forward
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Read through [project](../reference/library.md#project) function reference to see how the API works.
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There are a number of things to explore further in the tutorials section.
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[haskell.nix]: https://github.com/input-output-hk/haskell.nix
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