example.nix

with import <nixpkgs> {};
let
  ext = ext: path: let eL = builtins.stringLength ext;
                         pL = builtins.stringLength path;
                     in ext == builtins.substring (pL - eL) eL path;
  things = self: {
    odt2md = input: runCommand ("${builtins.baseNameOf input}.md") { buildInputs = [ pandoc ]; } ''
      pandoc -t markdown ${input} > $out
    '';
    fileList = builtins.attrNames (lib.filterAttrs (name: value: ext ".odt" name && value == "regular") (builtins.readDir ./.));
    mdList = map (file: self.odt2md (./. + "/${file}")) self.fileList;
    allMds = runCommand "all-the-mds" {} ''
      mkdir $out
      cat ${self.mdList} > $out/all-the-things.md
    '';
  };
in lib.fix things