system/nix/progs/nvim/coc_settings.nix

{
  languageserver = {
    nix = {
      command = "rnix-lsp";
      filetypes = ["nix"];
    };

    haskell = {
      command = "haskell-language-server-wrapper";
      args = ["--lsp"];
      rootPatterns = [
        "stack.yaml"
        ".cabal"
        "cabal.project"
        "package.yaml"
      ];
      filetypes = [
        "hs"
        "lhs"
        "haskell"
      ];
    };
  };

  # Rust
  "rust-analyzer.checkOnSave.command" = "clippy";
}