Re: Real constants

[Stefan Monnier]

>  - True constants can prevent some kinds of problems.

That seems to be the only real motivation (the others are more like "why not
have it"?).  I must say it's pretty vague.  AFAICT in 99.9% of the cases
constants have the following uses:

- catch programming errors.  This is similar to type annotations, modules,
  etc... and does not enable anything.  It's only used for software
  engineering purposes.
- allow the compiler to generate more efficient code.

I don't think Richard considers either of them as something
particularly important.

>  - At least one developer (Stefan) has said he has true constants
>    added to his local Emacs. I'd assume he finds them useful.

I like to experiment with primitives in order to get a better idea of what
the code out there looks like.  E.g. my local Emacs's strings are
non-mutable.  I.e. I like to try and add some constraint which seems to be
generally not broken, and see if/where it gets broken.  This is a general
technique to learn to understand some unknown piece of code.

Of course I also strongly believe in non-mutable objects, so I like the idea
of constants and non-mutable strings, but I know it's a waste of time to try
and include those things in elisp.


        Stefan