Probably not the right room to be asking (sorry), and I'm not sure there is an option that's more idiomatic. But I'll give my own recommendations and heuristics:

1. Always use explicit export lists so you only export the things you want exported. It's helpful to the compiler as well as your future self
2. Anything that needs a do block usually goes on the top level
3. lets and wheres are good for one-line unpacking or manipulating of function arguments, but it gets confusing if you can't see the place where the arguments are declared on the same screen
4. I usually put top-level helpers after the function they are helping, and I usually use let instead of where.
5. Nesting lets and wheres is awful

In reply to @b:chreekat.net

Probably not the right room to be asking (sorry), and I'm not sure there is an option that's more idiomatic. But I'll give my own recommendations and heuristics:

1. Always use explicit export lists so you only export the things you want exported. It's helpful to the compiler as well as your future self
2. Anything that needs a do block usually goes on the top level
3. lets and wheres are good for one-line unpacking or manipulating of function arguments, but it gets confusing if you can't see the place where the arguments are declared on the same screen
4. I usually put top-level helpers after the function they are helping, and I usually use let instead of where.
5. Nesting lets and wheres is awful

Well... the Haskell LSP is throwing errors for me on NixOS. I have it installed via my nix-shell:

{ pkgs ? import <nixpkgs> {} }:
let
  src = pkgs.nix-gitignore.gitignoreSource [] ./.;
  myPkg = pkgs.haskellPackages.callCabal2nix "aoc25" src {};
in
pkgs.stdenv.mkDerivation {
  name = "aoc-shell";

  buildInputs = [
    myPkg.env.nativeBuildInputs

    pkgs.cabal-install
    pkgs.haskell-language-server
    pkgs.hlint
    pkgs.ormolu
  ];
}

iqubic (she/her): One of

1. disable the hlint plugin in your editor config.

2. disable the hlint plugin by locally overriding the hls package

3. disable the hlint plugin by adding (and upstreaming) an override in nixpkgs

4. wait for the hls release which disables the hlint plugin to propagate to you.

5. or 4. needs to happen and needs to be backported to 25.11 because we shouldn’t have a broken hls there.

This isn't working for me (pkgs.haskell.lib.compose.disableCabalFlag "hlint" pkgs.haskell-language-server)

LATITUDE-NIXOS hs/aoc25 » nix-shell                                                                         127 ↵
fetching path input 'path:/nix/store/3w2nr2aq2gp76nb6lh1alx6h10mwvp5d-source'
building '/nix/store/mlbpkxipyf763cm4hcanls6wp3mm5vb1-cabal2nix-aoc25.drv'...
error:
       … while evaluating an expression to select 'drvPath' on it
         at «internal»:1:552:
       … while evaluating strict
         at «internal»:1:552:
       (stack trace truncated; use '--show-trace' to show the full trace)

       error: function 'anonymous lambda' called with unexpected argument 'mkDerivation'
       at /nix/store/3w2nr2aq2gp76nb6lh1alx6h10mwvp5d-source/pkgs/development/tools/haskell/haskell-language-server/withWrapper.nix:1:1:
            1| {
             | ^
            2|   lib,

       note: trace involved the following derivations:
       derivation 'aoc-shell'