ghcup-talk/GHCup.md

% GHCup % Julian Ospald % June 07, 2024

GHCup

What is GHCup?

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  • cabal distro packages constantly out of date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
• {#id .class height=32px} only supported linux and mac
• {#id .class height=32px} inspired by rustup

:::

GHCup today

::: incremental

• Haskell Survey 2022
  • 

• over 17k LOC Haskell
• supports all platforms: Linux, Windows, macOS, FreeBSD

:::

GHCup and haskell.org

::: incremental

• the default installer
  • 
• provides infrastructure (home page, downloads)

:::

GHCup and the Haskell Foundation

::: incremental

• affiliation: 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)?

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

::: incremental

• {#id .class width=32 height=32px} installer
• {#id .class width=32 height=32px} distribution channel
• {#id .class width=32 height=32px} feedback channel
• {#id .class width=32 height=32px} testing/QA gateway
• {#id .class width=32 height=32px} provider of sane defaults (e.g. "recommended" GHC version)
• {#id .class width=32 height=32px} glue for holistic toolchain experience
  • VSCode, stack, cabal-install integration
• {#id .class width=32 height=32px} CI provisioning (e.g. github actions)

:::

Upstream

Supported tools/dependencies:

::: incremental

• GHC
• Cabal
• HLS
• Stack

:::

Downstream

Users:

::: incremental

• {#id .class height=32px} Haskell developers
  • beginners, advanced, students, companies
• {#id .class width=32 height=32px} end users (e.g. compiling pandoc from source)
• {#id .class width=32 height=32px} GitHub CI
  • GitHub images, Haskell repos
• 🪞 mirrors
  • sjtug
• 🧰 tools
  • vscode-haskell, Haskell playground, nvim-lsp-installer

:::

How does it work?

::: incremental

• Architectural components
  • {#id .class height=32px} bootstrap scripts
  • {#id .class height=32px} ghcup binary (compiled)
  • {#id .class height=32px} ghcup-metadata (configuration files)
• Logical components
  • {#id .class height=32px} cli interface
  • {#id .class height=32px} file layout / installation destination
  • {#id .class height=32px} bindist selection
  • {#id .class height=32px} tui interface

:::

Basic CLI

::: incremental

• show all available tools / versions

  ghcup list
  

• install a tool

  ghcup install ghc latest
  

• make a tool version the default

  ghcup set ghc latest
  

• remove a tool version

  ghcup rm ghc 9.10.1
  

:::

Where does it install?

::: incremental

• root dir

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

• GHC and HLS are installed into sub-directories

  $ ls ~/.ghcup/ghc
  📁8.10.7 📁9.0.2 📁9.2.8
  

• bin directory is mostly symbolic links (compare with update-alternatives)

  $ 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