# Idris {#idris}
## Installing Idris {#installing-idris}
The easiest way to get a working idris version is to install the `idris` attribute:
```ShellSession
$ nix-env -f "<nixpkgs>" -iA idris
```
This however only provides the `prelude` and `base` libraries. To install idris with additional libraries, you can use the `idrisPackages.with-packages` function, e.g. in an overlay in `~/.config/nixpkgs/overlays/my-idris.nix`:
```nix
self: super: {
myIdris = with self.idrisPackages; with-packages [ contrib pruviloj ];
}
```
And then:
```ShellSession
$ # On NixOS
$ nix-env -iA nixos.myIdris
$ # On non-NixOS
$ nix-env -iA nixpkgs.myIdris
```
To see all available Idris packages:
```ShellSession
$ # On NixOS
$ nix-env -qaPA nixos.idrisPackages
$ # On non-NixOS
$ nix-env -qaPA nixpkgs.idrisPackages
```
Similarly, entering a `nix-shell`:
```ShellSession
$ nix-shell -p 'idrisPackages.with-packages (with idrisPackages; [ contrib pruviloj ])'
```
## Starting Idris with library support {#starting-idris-with-library-support}
To have access to these libraries in idris, call it with an argument `-p <library name>` for each library:
```ShellSession
$ nix-shell -p 'idrisPackages.with-packages (with idrisPackages; [ contrib pruviloj ])'
[nix-shell:~]$ idris -p contrib -p pruviloj
```
A listing of all available packages the Idris binary has access to is available via `--listlibs`:
```ShellSession
$ idris --listlibs
00prelude-idx.ibc
pruviloj
base
contrib
prelude
00pruviloj-idx.ibc
00base-idx.ibc
00contrib-idx.ibc
```
## Building an Idris project with Nix {#building-an-idris-project-with-nix}
As an example of how a Nix expression for an Idris package can be created, here is the one for `idrisPackages.yaml`:
```nix
{ lib
, build-idris-package
, fetchFromGitHub
, contrib
, lightyear
}:
build-idris-package {
name = "yaml";
version = "2018-01-25";
# This is the .ipkg file that should be built, defaults to the package name
# In this case it should build `Yaml.ipkg` instead of `yaml.ipkg`
# This is only necessary because the yaml packages ipkg file is
# different from its package name here.
ipkgName = "Yaml";
# Idris dependencies to provide for the build
idrisDeps = [ contrib lightyear ];
src = fetchFromGitHub {
owner = "Heather";
repo = "Idris.Yaml";
rev = "5afa51ffc839844862b8316faba3bafa15656db4";
sha256 = "1g4pi0swmg214kndj85hj50ccmckni7piprsxfdzdfhg87s0avw7";
};
meta = with lib; {
description = "Idris YAML lib";
homepage = "https://github.com/Heather/Idris.Yaml";
license = licenses.mit;
maintainers = [ maintainers.brainrape ];
};
}
```
Assuming this file is saved as `yaml.nix`, it's buildable using
```ShellSession
$ nix-build -E '(import <nixpkgs> {}).idrisPackages.callPackage ./yaml.nix {}'
```
Or it's possible to use
```nix
with import <nixpkgs> {};
{
yaml = idrisPackages.callPackage ./yaml.nix {};
}
```
in another file (say `default.nix`) to be able to build it with
```ShellSession
$ nix-build -A yaml
```
## Passing options to `idris` commands {#passing-options-to-idris-commands}
The `build-idris-package` function provides also optional input values to set additional options for the used `idris` commands.
Specifically, you can set `idrisBuildOptions`, `idrisTestOptions`, `idrisInstallOptions` and `idrisDocOptions` to provide additional options to the `idris` command respectively when building, testing, installing and generating docs for your package.
For example you could set
```nix
build-idris-package {
idrisBuildOptions = [ "--log" "1" "--verbose" ]
...
}
```
to require verbose output during `idris` build phase.