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haskell.nix/docs/reference/library.md
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1[Haskell.nix][] contains a library of functions for creating buildable
2package sets from their Nix expression descriptions. The library is
3what you get when importing [Haskell.nix][]. It might be helpful to
4load the library in the [Nix REPL](../user-guide.md#using-nix-repl) to
5test things.
7 * [Types](#types) — the kinds of data that you will encounter working with [Haskell.nix][].
8 * [Top-level attributes](#top-level-attributes) — Functions and derivations defined in the Haskell.nix attrset.
9 * [Package-set functions](#package-set-functions) — Helper functions defined on the `hsPkgs` package set.
11# Types
13## Package Set
15The result of `mkPkgSet`. This is an application of the NixOS module
16system.
18```
20 options = { ... };
21 config = {
22 hsPkgs = { ... };
23 packages = { ... };
24 compiler = {
25 version = "X.Y.Z";
26 nix-name = "ghcXYZ";
27 packages = { ... };
28 };
29 };
31```
33| Attribute | Type | Description |
34|----------------|------|-----------------------------------------------------|
35| `options` | Module options | The combination of all options set through the `modules` argument passed to `mkPkgsSet`. |
36| `config` | | The result of evaluating and applying the `options` with [Haskell.nix][] |
37| `.hsPkgs` | Attrset of [Haskell Packages](#haskell-package) | Buildable packages, created from `packages` |
38| `.packages` | Attrset of [Haskell Package descriptions](#haskell-package-descriptions) | Configuration for each package in `hsPkgs` |
39| `.compiler` | Attrset | |
43## Haskell Package description
45The _Haskell package descriptions_ are values of the
46`pkgSet.config.packages` attrset. These are not derivations, but just
47the configuration for building an individual package. The
48configuration options are described under `packages.<name>` in [Module
49options](./modules.md).
51## Component description
53The _component descriptions_ are values of the
54`pkgSet.config.packages.<package>.components` attrset. These are not
55derivations, but just the configuration for building an individual
56component. The configuration options are described under
57`packages.<name>.components.*` in [Module options](./modules.md).
60## Haskell Package
62In [Haskell.nix][], a _Haskell package_ is a derivation which has a
63`components` attribute. This derivation is actually just for the
64package `Setup.hs` script, and isn't very interesting. To actually use
65the package, look within the components structure.
67```
68components = {
69 library = COMPONENT;
70 exes = { NAME = COMPONENT; };
71 tests = { NAME = COMPONENT; };
72 benchmarks = { NAME = COMPONENT; };
73 all = COMPONENT;
75```
77## Component
79In [Haskell.nix][], a _component_ is a derivation corresponding to a
80[Cabal component](https://www.haskell.org/cabal/users-guide/developing-packages.html)
81of a package.
83[Haskell.nix][] also defines a special `all` component, which is the
84union of all components in the package.
86## Identifier
88A package identifier is an attrset pair of `name` and `version`.
90## Extras
92Extras allow adding more packages to the package set. These will be
93functions taking a single parameter `hackage`. They should return an
94attrset of package descriptions.
96## Modules
98Modules are the primary method of configuring building of the package
99set. They are either:
1011. an attrset containing [option declarations](./options.md), or
1022. a function that returns an attrset containing option declarations.
104If using the function form of a module, the following named parameters
105will be passed to it:
107| Argument | Type | Description |
108|------------------|------|---------------------|
109| `haskellLib` | attrset | The [haskellLib](#haskelllib) utility functions. |
110| `pkgs` | | The Nixpkgs collection. |
111| `pkgconfPkgs` | | A mapping of cabal build-depends names to Nixpkgs packages. (TODO: more information about this) |
112| `buildModules` | | |
113| `config` | | |
114| `options` | | |
117# Top-level attributes
119## mkStackPkgSet
121Creates a [package set](#package-set) based on the `pkgs.nix` output
122of `stack-to-nix`.
124```nix
125mkStackPkgSet =
126 { stack-pkgs, pkg-def-extras ? [], modules ? []}: ...
127```
129| Argument | Type | Description |
130|------------------|------|---------------------|
131| `stack-pkgs` | | `import ./pkgs.nix` — The imported file generated by `stack‑to‑nix`. |
132| `pkg‑def‑extras` | List of [Extras](#extras) | For overriding the package set. |
133| `modules` | List of [Modules](#modules) | For overriding the package set. |
135**Return value**: a [`pkgSet`](#package-set)
137## mkCabalProjectPkgSet
139Creates a [package set](#package-set) based on the `pkgs.nix` output
140of `plan-to-nix`.
142```nix
143mkCabalProjectPkgSet =
144 { plan-pkgs, pkg-def-extras ? [], modules ? []}: ...
145```
147| Argument | Type | Description |
148|------------------|------|---------------------|
149| `plan-pkgs` | | `import ./pkgs.nix` — The imported file generated by `plan‑to‑nix`. |
150| `pkg‑def‑extras` | List of [Extras](#extras) | For overriding the package set. |
151| `modules` | List of [Modules](#modules) | For overriding the package set. |
153**Return value**: a [`pkgSet`](#package-set)
155## mkPkgSet
157This is the base function used by both `mkStackPkgSet` and
158`mkCabalProjectPkgSet`.
160**Return value**: a [`pkgSet`](#package-set)
162## snapshots
164This is an attrset of `hsPkgs` packages from Stackage.
166## haskellPackages
168A `hsPkgs` package set, which is one of the recent LTS Haskell
169releases from [`snapshots`](#snapshots).
171The chosen LTS is updated occasionally in [Haskell.nix][], though a
172manual process.
174## nix-tools
176A derivation containing the `nix-tools` [command-line tools](commands.md).
178## callStackToNix
180## callCabalProjectToNix
182## hackage
183## stackage
185## fetchExternal
187## cleanSourceHaskell
189## haskellLib
191Assorted functions for operating on [Haskell.nix][] data. This is
192distinct from `pkgs.haskell.lib` in the current Nixpkgs Haskell
193Infrastructure.
195# Package-set functions
197These functions exist within the `hsPkgs` package set.
199## shellFor
201Create a `nix-shell` [development
202environment](../user-guide/development.md) for developing one or more
203packages.
205```
206shellFor =
207 { packages, withHoogle ? true, ...}: ...
208```
211| Argument | Type | Description |
212|----------------|------|---------------------|
213| `packages` | Function | Package selection function. It takes a list of [Haskell packages](#haskell-package) and returns a subset of these packages. |
214| `withHoogle` | Boolean | Whether to build a Hoogle documentation index and provide the `hoogle` command. |
215| `{ ... }` | Attrset | All the other arguments are passed to [`mkDerivation`](https://nixos.org/nixpkgs/manual/#sec-using-stdenv). |
217**Return value**: a derivation
219## ghcWithPackages
221Creates a `nix-shell` [development
222environment](../user-guide/development.md) including the given
223packages selected from this package set.
225**Parameter**: a package selection function.
227**Return value**: a derivation
229**Example**:
231```
232haskell.haskellPackages.ghcWithPackages (ps: with ps; [ lens conduit ])
233```
235## ghcWithHoogle
237The same as `ghcWithPackages`, except, a `hoogle` command with a
238Hoogle documentation index of the packages will be included in the
239shell.
241[haskell.nix]: https://github.com/input-output-hk/haskell.nix