187 lines
7.1 KiB
Markdown
187 lines
7.1 KiB
Markdown
# Agda {#agda}
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## How to use Agda
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Agda is available as the [agda](https://search.nixos.org/packages?channel=unstable&show=agda&from=0&size=30&sort=relevance&query=agda)
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package.
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The `agda` package installs an Agda-wrapper, which calls `agda` with `--library-file`
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set to a generated library-file within the nix store, this means your library-file in
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`$HOME/.agda/libraries` will be ignored. By default the agda package installs Agda
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with no libraries, i.e. the generated library-file is empty. To use Agda with libraries,
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the `agda.withPackages` function can be used. This function either takes:
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* A list of packages,
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* or a function which returns a list of packages when given the `agdaPackages` attribute set,
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* or an attribute set containing a list of packages and a GHC derivation for compilation (see below).
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* or an attribute set containing a function which returns a list of packages when given the `agdaPackages` attribute set and a GHC derivation for compilation (see below).
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For example, suppose we wanted a version of Agda which has access to the standard library. This can be obtained with the expressions:
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```nix
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agda.withPackages [ agdaPackages.standard-library ]
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```
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or
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```nix
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agda.withPackages (p: [ p.standard-library ])
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```
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or can be called as in the [Compiling Agda](#compiling-agda) section.
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If you want to use a different version of a library (for instance a development version)
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override the `src` attribute of the package to point to your local repository
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```nix
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agda.withPackages (p: [
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(p.standard-library.overrideAttrs (oldAttrs: {
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version = "local version";
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src = /path/to/local/repo/agda-stdlib;
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}))
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])
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```
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You can also reference a GitHub repository
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```nix
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agda.withPackages (p: [
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(p.standard-library.overrideAttrs (oldAttrs: {
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version = "1.5";
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src = fetchFromGitHub {
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repo = "agda-stdlib";
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owner = "agda";
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rev = "v1.5";
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sha256 = "16fcb7ssj6kj687a042afaa2gq48rc8abihpm14k684ncihb2k4w";
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};
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}))
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])
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```
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If you want to use a library not added to Nixpkgs, you can add a
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dependency to a local library by calling `agdaPackages.mkDerivation`.
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```nix
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agda.withPackages (p: [
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(p.mkDerivation {
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pname = "your-agda-lib";
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version = "1.0.0";
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src = /path/to/your-agda-lib;
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})
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])
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```
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Again you can reference GitHub
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```nix
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agda.withPackages (p: [
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(p.mkDerivation {
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pname = "your-agda-lib";
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version = "1.0.0";
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src = fetchFromGitHub {
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repo = "repo";
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owner = "owner";
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version = "...";
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rev = "...";
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sha256 = "...";
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};
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})
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])
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```
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See [Building Agda Packages](#building-agda-packages) for more information on `mkDerivation`.
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Agda will not by default use these libraries. To tell Agda to use a library we have some options:
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* Call `agda` with the library flag:
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```ShellSession
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$ agda -l standard-library -i . MyFile.agda
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```
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* Write a `my-library.agda-lib` file for the project you are working on which may look like:
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```
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name: my-library
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include: .
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depend: standard-library
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```
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* Create the file `~/.agda/defaults` and add any libraries you want to use by default.
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More information can be found in the [official Agda documentation on library management](https://agda.readthedocs.io/en/v2.6.1/tools/package-system.html).
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## Compiling Agda
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Agda modules can be compiled using the GHC backend with the `--compile` flag. A version of `ghc` with `ieee754` is made available to the Agda program via the `--with-compiler` flag.
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This can be overridden by a different version of `ghc` as follows:
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```nix
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agda.withPackages {
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pkgs = [ ... ];
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ghc = haskell.compiler.ghcHEAD;
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}
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```
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## Writing Agda packages
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To write a nix derivation for an Agda library, first check that the library has a `*.agda-lib` file.
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A derivation can then be written using `agdaPackages.mkDerivation`. This has similar arguments to `stdenv.mkDerivation` with the following additions:
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* `everythingFile` can be used to specify the location of the `Everything.agda` file, defaulting to `./Everything.agda`. If this file does not exist then either it should be patched in or the `buildPhase` should be overridden (see below).
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* `libraryName` should be the name that appears in the `*.agda-lib` file, defaulting to `pname`.
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* `libraryFile` should be the file name of the `*.agda-lib` file, defaulting to `${libraryName}.agda-lib`.
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Here is an example `default.nix`
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```nix
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{ nixpkgs ? <nixpkgs> }:
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with (import nixpkgs {});
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agdaPackages.mkDerivation {
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version = "1.0";
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pname = "my-agda-lib";
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src = ./.;
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buildInputs = [
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agdaPackages.standard-library
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];
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}
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```
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### Building Agda packages
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The default build phase for `agdaPackages.mkDerivation` simply runs `agda` on the `Everything.agda` file.
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If something else is needed to build the package (e.g. `make`) then the `buildPhase` should be overridden.
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Additionally, a `preBuild` or `configurePhase` can be used if there are steps that need to be done prior to checking the `Everything.agda` file.
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`agda` and the Agda libraries contained in `buildInputs` are made available during the build phase.
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### Installing Agda packages
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The default install phase copies Agda source files, Agda interface files (`*.agdai`) and `*.agda-lib` files to the output directory.
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This can be overridden.
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By default, Agda sources are files ending on `.agda`, or literate Agda files ending on `.lagda`, `.lagda.tex`, `.lagda.org`, `.lagda.md`, `.lagda.rst`. The list of recognised Agda source extensions can be extended by setting the `extraExtensions` config variable.
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## Adding Agda packages to Nixpkgs
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To add an Agda package to `nixpkgs`, the derivation should be written to `pkgs/development/libraries/agda/${library-name}/` and an entry should be added to `pkgs/top-level/agda-packages.nix`. Here it is called in a scope with access to all other Agda libraries, so the top line of the `default.nix` can look like:
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```nix
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{ mkDerivation, standard-library, fetchFromGitHub }:
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```
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Note that the derivation function is called with `mkDerivation` set to `agdaPackages.mkDerivation`, therefore you
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could use a similar set as in your `default.nix` from [Writing Agda Packages](#writing-agda-packages) with
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`agdaPackages.mkDerivation` replaced with `mkDerivation`.
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Here is an example skeleton derivation for iowa-stdlib:
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```nix
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mkDerivation {
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version = "1.5.0";
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pname = "iowa-stdlib";
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src = ...
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libraryFile = "";
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libraryName = "IAL-1.3";
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buildPhase = ''
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patchShebangs find-deps.sh
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make
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'';
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}
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```
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This library has a file called `.agda-lib`, and so we give an empty string to `libraryFile` as nothing precedes `.agda-lib` in the filename. This file contains `name: IAL-1.3`, and so we let `libraryName = "IAL-1.3"`. This library does not use an `Everything.agda` file and instead has a Makefile, so there is no need to set `everythingFile` and we set a custom `buildPhase`.
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When writing an Agda package it is essential to make sure that no `.agda-lib` file gets added to the store as a single file (for example by using `writeText`). This causes Agda to think that the nix store is a Agda library and it will attempt to write to it whenever it typechecks something. See [https://github.com/agda/agda/issues/4613](https://github.com/agda/agda/issues/4613).
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