ghcup/README.md

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[`cabal-install`](https://hackage.haskell.org/package/cabal-install) manages Haskell library dependencies and can select a specific version of `ghc` (see [`with-compiler`](https://cabal.readthedocs.io/en/latest/nix-local-build.html#cfg-flag---with-compiler)). However, `cabal` will fail if the required version is not available and many operating systems do not offer a way to install specific versions of `ghc`.

`ghcup` makes it easy to install specific versions of `ghc` on GNU/Linux, and can also bootstrap a fresh Haskell developer environment from scratch.

Inspired by [rustup](https://github.com/rust-lang-nursery/rustup.rs), [pyenv](https://github.com/pyenv/pyenv) and [jenv](http://www.jenv.be).

*OS X users may prefer [futurice](https://haskell.futurice.com/) and Ubuntu users may prefer [hvr's ppa](https://launchpad.net/~hvr/+archive/ubuntu/ghc).*

**Note: this project is in early stage and may not work on all distributions yet!**

## Table of Contents

   * [Installation](#installation)
   * [How](#how)
   * [Usage](#usage)
   * [Contributing](#contributing)
   * [TODO](#todo)
   * [Known problems](#known-problems)

## Installation

Just place the `ghcup` shell script into your `PATH` anywhere.

E.g.:

```sh
mkdir -p ~/.local/bin
curl https://raw.githubusercontent.com/haskell/ghcup/master/ghcup > ~/.local/bin/ghcup
chmod +x ~/.local/bin/ghcup
```

Then adjust your `PATH` in `~/.bashrc` (or similar, depending on your shell) like so, for example:

```sh
export PATH="$HOME/.cabal/bin:$HOME/.ghcup/bin:$HOME/.local/bin:$PATH"
```

## How

Installs a specified GHC version into `~/.ghcup/ghc/<ver>`,
and places `ghc-<ver>` etc. symlinks in `~/.ghcup/bin/`.
Additionally allows to manage currently selected ghc
via unversioned symlinks.

This uses precompiled GHC binaries that have been
compiled on fedora/debian by
[upstream GHC](https://www.haskell.org/ghc/download_ghc_8_6_1.html#binaries).

Alternatively, you can also tell it to compile from source (note that this might
fail due to missing requirements).

In addition this script can also install `cabal-install`.

## Usage

See `ghcup --help`.

## Contributing

* PR or email
* this script is POSIX shell
* use [shellcheck](https://github.com/koalaman/shellcheck) and `checkbashisms.pl` from [debian devscripts](http://http.debian.net/debian/pool/main/d/devscripts/devscripts_2.18.4.tar.xz)
* whitespaces, no tabs

## TODO

- [ ] FreeBSD support ([#4](https://github.com/haskell/ghcup/issues/4))
- [ ] Make fetching tarballs more robust ([#5](https://github.com/haskell/ghcup/issues/5))
- [x] More code documentation
- [x] Allow to compile from source ([#2](https://github.com/haskell/ghcup/issues/2))
- [x] Allow to install cabal-install as well ([#3](https://github.com/haskell/ghcup/issues/3))

## Known problems

### Precompiled binaries

Since this uses precompiled binaries you may run into
problems with *ncurses* and **missing libtinfo**, in case
your distribution doesn't use the legacy way of building
ncurses and has no compatibility symlinks in place.

Ask your distributor on how to solve this or
try to compile from source via `ghcup compile <version>`.

### Unreliable download location

There is no single reliable URL where to download future
GHC binary releases from, since the tarball names contain
the distro name and version they were built on. As such,
we cannot foresee what will be the next tarball name.

In such a case, consider to update this script via
`ghcup self-update`.

### Compilation

Although this script can compile GHC for you, it's just a very thin
wrapper around the build system. It makes no effort in trying
to figure out whether you have the correct toolchain and
the correct dependencies. Refer to [the official docs](https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Linux)
on how to prepare your environment for building GHC.