`quit_char', `set-quit-char', and `set-input-mode'

`quit_char', `set-quit-char', and `set-input-mode'

[Drew Adams]

* Variable `quit-char' is only in the C code. There is no such Lisp variable.

* Function `set-quit-char' exists, but is not even mentioned in the Elisp
manual.

* Function `set-input-mode' is mentioned in the manual, but it just seems more
roundabout than `set-quit-char'.

Why isn't `set-quit-char' documented as the way to set the quit character?  Is
there some advantage to using `set-input-mode' for this?
 
Why don't we have a Lisp variable for this (even a user option perhaps)?  Why
must we use special functions to set this character, rather than just using
`set' with a variable?
 
If we had a variable, then code could check whether some event was equal to the
quit character, instead of checking only the hard-coded value 7 (C-g).  If
something changes the `quit_char' from C-g to something else, then code testing
7 will no longer DTRT, no?
 
I'm guessing there are good reasons for some or all of these things - reasons
that would help me understand better. Explanation appreciated.
 

Re: `quit_char', `set-quit-char', and `set-input-mode'

[Thien-Thi Nguyen]

() "Drew Adams" <drew.adams@oracle.com>
() Fri, 11 May 2012 16:55:46 -0700

   I'm guessing there are good reasons for some or all of
   these things - reasons that would help me understand
   better.  Explanation appreciated.

I ported Emacs 22 to VMS a while back, and fuzzily remember
playing w/ this corner (changing things to see what breaks).
Based on this, i would say these things are the way they are
primarily due to tradition (C-g ≡ ASCII BEL, which makes a
‘ding’, uncoincidentally) and inertia (no one has bothered
{ration,gener}alizing things further).  That is also a guess.