[klibertp]

As you can easily check with M-x find-function a `scroll-up` function is implemented in C. This is a known problem - I can't find it right now, but I remember I once read a blog post where the author complained about this: in general you're not going to get good results when trying to advise, override or modify C-level functions from Elisp code.

IIRC cl-flet was recently (well, in the current decade I think :)) modified to be lexically scoped, so that won't work (anymore). This is why I had to use `letf` with `(symbol-function 'symbol)` instead of a neater `(flet ((beep ())) ...)`.

Personally I deal with beeping like this:

    (setq ring-bell-function (lambda ()))

but this disables any beeping, which may not be what you want. In short, things you `setq` or more generally `setf` tend to be visible from C functions (no guarantees though).

On the other hand my Emacs (on Linux) refuses to beep in any circumstances even if I run it with `emacs -Q` and do M-: (beep) - I have no idea why, I suspect it's either my sound configuration or has to do with the way I built my emacs from source.

I'd say for this:

    (funcall
      (funcall
          (lambda (a) (lambda (b) a))
          1)
      2)

raising a (void-variable a) error is correct behaviour under dynamic scoping. On my system (Emacs 25.0.50.2 x86_64-unknown-linux-gnu) it fails with void-variable under normal circumstances, but returns 1 when used with lexical scoping enabled. If your Emacs behaves differently (and remember to always check with emacs -Q just to be sure it's not something in your config) that's probably a bug.

[hollerith]

>If your Emacs behaves differently . . . that's probably a bug.

Yes, it behaves differently (with lexical-binding set to t and with the -Q flag).