Suntheme

Runs a script on sunrise and sunset, written in pure Haskell

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You may be wondering how a program written in Haskell, the purely functional programming language, could possibly act on the real world by running a so-called "script."

It's simple. We take in the entire World as an input to a pure function, the IO Monad. It then maps the original World to a new (generated) World, with our desired IO actions carefully applied with mathematical precision.

From the second perspective, an IO action transforms the whole world. IO actions are actually pure, because they receive a unique world as an argument and then return the changed world.

See this for more information.

Furthermore, you may wonder how this suntheme could possibly be used on a purely functional Linux distribution, like NixOS. Wouldn't mutating the system colorscheme be pathologically changing the system state? This is simple as well. We simply utilize the NixOS specializations feature to generate two copies of every single generation, one in dark and one in light theme, and then swap out the entire system. Therefore no state is mutated and the user simply gets swapped onto a specialized generation of NixOS with their desired colorscheme. Behold: the genius of purely functional programming.

Work is ongoing to create a turnkey drop-in NixOS module that interfaces with Stylix to automatically create the system color activation scripts and expose them to suntheme.

Hacking on suntheme

It's trivial to get started with suntheme development thanks to Nix, the purely functional package manager. Naturally, we leverage it as our primary package manager, both for Hackage and development tools like language servers and the like.

First, install Nix through your preferred avenue or local system administrator. If unsure, we recommend the Determinate Nix Installer. Make sure flakes and nix-command are enabled (the Determinate Installer will enable them by default).

Once you have nix, simply type:

nix develop

Say yes to any prompts asking you to allow substituters or trust public keys. Nix will fetch all of the required packages, such as GHC and Hackage dependencies. Additionally, you will have access to hlint and the haskell-language-server.

To create a build, type

nix build

A binary will be produced in result/bin/suntheme.

To make suntheme available in the shell without outputting to result, use

nix shell

This will build a binary just like nix build but add it temporarily to the PATH, so you can just type suntheme.

To build and run suntheme immediately without adding it to the PATH, use

nix run

This will build a binary just like nix shell but immediately execute it.