Cliff Harvey fieldstrength

Since macOS Catalina, the root drive is read-only. The solution is to create a separate APFS volume and a “synthetic” /nix directory which points to it:

# Check if /nix exists, if not:
echo 'nix' | sudo tee -a /etc/synthetic.conf
# this will create a "synthetic" empty directory /nix

# REBOOT so macOS sees the synthetic directory

# After rebooting, create an APFS volume for Nix

	{-# LANGUAGE GADTs, RankNTypes, TypeFamilies, DataKinds, PolyKinds, TypeOperators, ScopedTypeVariables #-}

	-- Lots of ways you can phrase this, but this works for me
	-- For folks who haven't seen it before, this is "the essence of the sum type" and sigma stands for sum.
	-- You see it far more often in dependent types than elsewhere because it becomes a lot more pleasant to
	-- work with there, but it's doable in other contexts too. Think of the first parameter to the data
	-- constructor as a generalized "tag" as we talk about in "tagged union", and the second parameter is the
	-- "payload". It turns out that you can represent any simple sum type you could write in Haskell this way
	-- by using a finite and enumerable `f`, but things can get more unusual when `f` isn't either. In such
	-- cases, it's often easier to think of this as the essence of existential types.