;; -*- lexical-binding: t -*-

(defun backtrace-1 (evald func args flags)
  "Print a trace of a single stack frame to `standard-output'.
EVALD, FUNC, ARGS, FLAGS are as in `mapbacktrace'."
  (let ((print-level (or print-level 8)))
    (princ (if (plist-get flags :debug-on-exit) "* " "  "))
    (cond
     ((and evald (not debugger-stack-frame-as-list))
      (prin1 func)
      (if args (prin1 args) (princ "()")))
     (t
      (prin1 (cons func args))))
    (princ "\n")))

(defun backtrace ()
  "Print a trace of Lisp function calls currently active.
Output stream used is value of `standard-output'."
  (mapbacktrace #'backtrace-1 'backtrace))

(backtrace)

(defun backtrace-frames ()
  "Collect all frames of current backtrace into a list."
  (let ((frames nil))
    (mapbacktrace (lambda (&rest frame) (push frame frames)) 'backtrace-frames)
    (nreverse frames)))

(backtrace-frames)

(defun ~/backtrace-frame (nframes &optional base)
  "Return the function and arguments NFRAMES up from current execution point.
If that frame has not evaluated the arguments yet (or is a special form),
the value is (nil FUNCTION ARG-FORMS...).
If that frame has evaluated its arguments and called its function already,
the value is (t FUNCTION ARG-VALUES...).
A &rest arg is represented as the tail of the list ARG-VALUES.
FUNCTION is whatever was supplied as car of evaluated list,
or a lambda expression for macro calls.
If NFRAMES is more than the number of frames, the value is nil.
If BASE is non-nil, it should be a function and NFRAMES counts from its
nearest activation frame."
  (let ((frame nil))
    (mapbacktrace (lambda (evald func args _)
                    (when (and base (eq func base))
                      (setq base nil))
                    (unless base
                      (when (eq nframes 0)
                        (setq frame `(,evald ,func ,@args)))
                      (setq nframes (1- nframes))))
                  '~/backtrace-frame)
    frame))