haskell-quick-nix-build

(defun haskell-quick-nix-build ()
  (interactive)
  (when-let ((original-directory (file-name-directory (buffer-file-name))))
    (let ((current-directory original-directory))
      (while (and
              (not
               (or
                (string= current-directory (expand-file-name "~"))
                (string= current-directory (expand-file-name "/"))))
              (not (directory-files current-directory nil "cabal$")))
        (setq current-directory         ;this is gross
              (mapconcat 'identity
                         (reverse
                          (cons ""
                                (cdr
                                 (cdr
                                  (reverse
                                   (split-string
                                    current-directory
                                    "/"))))))
                         "/")))
      (unwind-protect
          (not-if (directory-files current-directory nil "cabal$")
              (message "Could not find a cabal file.")
            (cd current-directory)
            (compile "nix-shell --run \"cabal build\"" t))
        (cd original-directory)))))