Question

I am trying to call a bash program herbstclient from Emacs via process-lines. I created a macro hc-call which actually calls herbstclient that is invoked by the function hc which is supposed to convert its numeric arguments into strings via stringify-numbers.

Needless to say it’s not working. Calling hc with “keybind” “Mod4-Shift-r” “reload” gives the error:

 *** Eval error ***  Wrong type argument: listp, stringified-args

I tried using edebug on hc and the output suggested stringify-numbers was working properly. The function errored immediately on the hc-call. Yet, when I run:

(hc-call ("keybind" "Mod4-Shift-r" "reload"))

it works as expected. I then tried:

(setq sargs (list "keybind" "Mod4-Shift-r" "reload"))
(hc-call sargs)

and I got the same error. I don’t know how to approach debugging this further. Below is all the code:

(defmacro hc-call (args)
  "Call herbstclient to with the given arguments."
   `(process-lines "herbstclient" ,@args))

(defun stringify-numbers (args)
  "Take a list of random arguments with a mix of numbers and
  strings and convert just the numbers to strings."
  (let (stringified-args)
    (dolist (arg args)
      (if (numberp arg)
          (setq stringified-args (cons (number-to-string arg) stringified-args))
        (setq stringified-args (cons arg stringified-args))))
    (nreverse stringified-args)))

(defun hc (&rest args)
  "Pass arguments to herbstclient in a bash process."
  (let ((stringified-args (stringify-numbers args)))
    (hc-call stringified-args)))

Why would it complain stringified-args isn’t a list?

Answer 1

Unlike most expressions, macro arguments are passed unevaluated.

This is why (hc-call ("keybind" "Mod4-Shift-r" "reload")) does not result in an error!

It therefore follows that (hc-call sargs) is passing the symbol sargs to the macro, rather than the list to which it would otherwise evaluate.

If you wish your macro to process a variable in this way, you could change ,@args to ,@(eval args), or else conditionally process args either way, depending on what it turns out to actually be.