FIXME: This is a hacked version of tinc, which breaks the Nix output in order

to avoid globals and allow more overriding. If it is useful, it should be

cleaned up (e.g. integrated into the existing output, rather than replacing

it) and upstreamed!

tinc: A dependency manager for Haskell

tinc installs dependencies for a project that you work on into a sandbox. While doing so it caches installed packages (in ~/.tinc/cache). When a package with the same transitive dependencies is already in the cache, it reuses that cached package instead of building it again.

tinc uses an exact algorithm for determining reusability. This guarantees 100% cache reuse. A package with the same transitive dependencies is never built twice.

tinc does not take any cached packages into account when resolving dependencies. Running

$ tinc

gives you the exact same result as

$ cabal sandbox delete
$ cabal sandbox init
$ cabal install --only-dependencies --enable-tests

tinc is idempotent. It's safe to run tinc multiple times. Running tinc after changing the .cabal-file of a project or after running cabal update results in a new updated sandbox.

If tinc fails / terminates for some reason, it does not modify anything (neither the cache nor any existing sandboxes). Interrupting a running tinc build is always safe.

Optionally use Nix for package caching

By default, tinc maintains its own package cache under ~/.tinc/cache.

However, it can optionally use nixpkgs for package caching. If tinc is installed somewhere under /nix, this is the default.

To change the default, you can set the environment variable TINC_USE_NIX to either yes or no, specifically:

export TINC_USE_NIX=yes  # use nix, even if not installed under /nix
export TINC_USE_NIX=no   # do not use nix, even if installed under /nix