I’m quite new to nix flakes, and have pieced togather a broken devshell, but am not sure why it is broken.
This is the error

error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'ghc-shell-for-next-step-haskell-0.1.0.0'
         whose name attribute is located at /nix/store/m9s94alic7s2r6v47p7lwfj58ibc076a-source/pkgs/stdenv/generic/make-derivation.nix:353:7

       … while evaluating attribute 'shellHook' of derivation 'ghc-shell-for-next-step-haskell-0.1.0.0'

         at /nix/store/8fby8siik8lv2z5k99lq7v83nch325dg-source/flake.nix:100:15:

           99|
          100|               shellHook = ''
             |               ^
          101|                  ${pkgs.lolcat}/bin/lolcat ${./fig}

       error: value is a function while a set was expected

Here is the link to the project where you find flake.nix and server/default.nix. Pointing me in a direction, links to relevent info, much appreciated.