ghcup-talk/GHCup.md

% GHCup
% Julian Ospald
% June 07, 2024

# GHCup

## What is GHCup?

![](what.jpg)

## State of 2019

::: incremental

* stack is the only "Haskell Installer"
* no unified alternative for cabal users
* distro packages, nix, manual installs, ...
* 🤮

:::

## How it started

::: incremental

* 🤹 small team at work (Capital Match), using different platforms
  - originally used stack
  - cabal distro packages constantly out of date
* 🦾 first version was 165 LOC
  - Posix shell
* ![](linux.png){#id .class height=32px} only supported linux and mac
* ![](rust.png){#id .class height=32px} inspired by **rustup**

:::

## GHCup today

::: incremental

* [Haskell Survey 2022](https://taylor.fausak.me/2022/11/18/haskell-survey-results/#s2q1)
  * ![](survey.png)
- over **17k** LOC Haskell
- supports all platforms: Linux, Windows, macOS, FreeBSD

:::

## GHCup and haskell.org

::: incremental

* the default installer
  - ![](downloads.png)
* provides infrastructure (home page, downloads)

:::

## GHCup and the Haskell Foundation

::: incremental

* affiliation: [https://haskell.foundation/affiliates/](https://haskell.foundation/affiliates/)
* pays for CI
* pays consultants to assist the project

:::

## What is a good installer?

::: incremental

* it installs (just that)
  - everywhere
* intuitive interface
  - `ghcup install ghc`
* good documentation
  - but you shouldn't have to read it
* get out of the way
  - has no self-fulfilling purpose

:::

## Goals and principles

::: incremental

- ☮️ unification
- unix principles
  - 🛠️ do one thing and do it well
  - ⚗️ pipes, compose stdout and stdin (re-usable)
- 🎁 good re-distribution
- 🛣️ user experience

:::

## What is GHCup (simplified)?

```sh
curl -s -L 'https://downloads.haskell.org/~ghc/9.6.5/ghc-9.6.5-x86_64-fedora33-linux.tar.xz' |
  tar -xJ -C /tmp                              &&
  cd /tmp/ghc-9.6.5-x86_64-unknown-linux/      &&
  ./configure --prefix="$HOME/.local"          &&
  make install                                 &&
  rm -rf /tmp/ghc-9.6.5-x86_64-unknown-linux/
```



## What is GHCup really?

* [https://hasufell.github.io/posts/2023-11-14-ghcup-is-not-an-installer.html](https://hasufell.github.io/posts/2023-11-14-ghcup-is-not-an-installer.html)

::: incremental

* ![](open-box.png){#id .class width=32 height=32px} installer
* ![](debian.png){#id .class width=32 height=32px} distribution channel
* ![](feedback.png){#id .class width=32 height=32px} feedback channel
* ![](qa.png){#id .class width=32 height=32px} testing/QA gateway
* ![](user.png){#id .class width=32 height=32px} provider of sane defaults (e.g. "recommended" GHC version)
* ![](chain-saw.png){#id .class width=32 height=32px} glue for holistic toolchain experience
  - VSCode, stack, cabal-install integration
* ![](ghaction.png){#id .class width=32 height=32px} CI provisioning (e.g. github actions)

:::

## Upstream

Supported tools/dependencies:

::: incremental

- GHC
- Cabal
- HLS
- Stack

:::

## Downstream

Users:

::: incremental

- ![](haskell_logo.png){#id .class height=32px} Haskell developers
  - beginners, advanced, students, companies
- ![](person.png){#id .class width=32 height=32px} end users (e.g. compiling pandoc from source)
- ![](ghaction.png){#id .class width=32 height=32px} GitHub CI
  - GitHub images, Haskell repos
- 🪞 mirrors
  - [sjtug](https://mirror.sjtu.edu.cn/docs/ghcup)
- 🧰 tools
  - [vscode-haskell](https://github.com/haskell/vscode-haskell), [Haskell playground](https://play.haskell.org/), [nvim-lsp-installer](https://github.com/williamboman/nvim-lsp-installer)

:::

## How does it work?

::: incremental

* **Architectural components**
    - ![](sh-file.png){#id .class height=32px} bootstrap scripts
    - ![](exe-file.png){#id .class height=32px} ghcup binary (compiled)
    - ![](config-file.png){#id .class height=32px} ghcup-metadata (configuration files)
* **Logical components**
    - ![](terminal.png){#id .class height=32px} cli interface
    - ![](file.png){#id .class height=32px} file layout / installation destination
    - ![](tar.png){#id .class height=32px} bindist selection
    - ![](brick-final-clearbg.png){#id .class height=32px} tui interface

:::

## Basic CLI

::: incremental

* show all available tools / versions
  ```sh
  ghcup list
  ```
* install a tool
  ```sh
  ghcup install ghc latest
  ```
* make a tool version the default
  ```sh
  ghcup set ghc latest
  ```
* remove a tool version
  ```sh
  ghcup rm ghc 9.10.1
  ```

:::

## Where does it install?

::: incremental

* root dir
  ```sh
  $ ls ~/.ghcup
  📁bin 📁ghc 📁hls
  📁cache 📁db 📁logs 📁tmp 🗑️trash 📄config.yaml 📄env
  ```

* GHC and HLS are installed into sub-directories
  ```sh
  $ ls ~/.ghcup/ghc
  📁8.10.7 📁9.0.2 📁9.2.8
  ```

* bin directory is mostly symbolic links (compare with [update-alternatives](https://man7.org/linux/man-pages/man1/update-alternatives.1.html))
  ```sh
  $ ls ~/.ghcup/bin
  📄ghcup
  🔗cabal 📄cabal-3.10.3.0
  🔗ghc 🔗ghc-8.10 🔗ghc-8.10.7 🔗ghc-9.0 🔗ghc-9.0.2 🔗ghc-9.2 🔗ghc-9.2.8
  ```
:::

## Bindist selection

* TODO