Yep, 4 GB RAM and 2 GB swap not enough to install pandoc in Nix. It failed at or after "copying path '/nix/store/3cv3s9lv79qjkqyafbclbk03gz5z813w-ghc-8.2.2' from 'https://cache.nixos.org'..."
Upped it to 8 GB swap and then it worked. It peaked around 1.6 GB swap as far as I could catch in `top`.
#nix