Re: About an example in Emacs Lisp manual

[Xue Fuqiao]

On Sun, 10 Feb 2013 15:07:29 +0000
Tom Capey <tom.capey@gmail.com> wrote:

> * Xue Fuqiao writes:
> > In (info "(elisp) Translation Keymaps"):
> >     For example, here's how to define `C-c h' to turn the character that
> >   follows into a Hyper character:
> >      (defun hyperify (prompt)
> >        (let ((e (read-event)))
> >          (vector (if (numberp e)
> >                      (logior (lsh 1 24) e)
> >                    (if (memq 'hyper (event-modifiers e))
> >                        e
> >                      (add-event-modifier "H-" e))))))
[...]
>   The Hyper modifier bit is the 2^24 bit--(info "(elisp) Other Char Bits").
>   If that bit is a 1 then it's on, 0 and it's off.
>   (lsh 1 n) returns a value with just the nth bit turned on, and
>   all the other bits are turned off, that is, are zero.  Thus
>   (lsh 1 24) has the 2^24 bit turned on [(= (expt 2 24) (lsh 1 24)) => t],
>   the Hyper modifier bit.
>   `logior' does a bit-by-bit OR comparision between the number
>   with its 24th bit on and `e', looking at both numbers as though
>   they were binary representations.  In this case we're OR-ing
>   `e' against the Hyper bit, and this has the effect of returning
>   `e' with the Hyper bit turned on.

Ah, I see.  Thanks for your explanation.

> /Tom
-- 
Best regards, Xue Fuqiao.
http://www.emacswiki.org/emacs/XueFuqiao