Re: e and pi

[Deniz Dogan <deniz.a.m.dogan@gmail.com>]

2010/9/16 Stefan Monnier <monnier@iro.umontreal.ca>:
> As you may have noticed, I have added a new warning to the byte-compiler
> for defvars of variables that don't have a prefix.  This is in
> preparation for the introduction of lexical scoping: in order not to
> have to rewrite all the code, the lexbind branch uses `let' both for
> dynamically-scoped let-bindings and for lexically-scoped let-bindings;
> where the distinction is based on whether or not a variable has
> been defvar'd.  This is the same system as used in Common-Lisp and it
> works well in practice, but it requires a bit of care, because every
> defvar has a global effect: it declares that this variable will use
> dynamic-scoping wherever it gets let-bound.  So if a file uses `len' as
> a lexically-scoped variable and another file does a (defvar len), we get
> a conflict that results in the first file being evaluated with
> a different semantic than expected by the author.
>
> So, the end result is that (defvar <prefix>-<foo>) is OK because the
> "<prefix>-" ensures you only mess with your own variable, but (defvar
> <foo>) is not OK because you may interfere with some other package.
>
> Now, we have a lot of offending (defvar <foo>) in Emacs currently, so we
> will want to fix them, and to get things started, we want to fix the two
> predefined float constants `e' and `pi'.
>
> In their case, the solution is to rename them to `float-e' and
> `float-pi', but this introduces a backward incompatibility.
> I figure we could define-obsolete-variable-alias (which leaves the
> problem of `e' and `pi' being dynamically scoped, but hopefully only
> for a few versions until we remove the obsolete name), but this means
> that every code that does (let ((e <foo>)) ...) would now get a stupid
> warning about using an obsolete variable `e'.
>
> So I intend to do the following:
> - in Emacs-23.3, define `e', `float-e', `pi', and `float-pi' and declare
>  `e' and `pi' obsolete, but without a make-obsolete-variable
>  (i.e. only in NEWS and in docstrings).
> - in Emacs-24 keep float-e and float-pi but get rid of `e' and `pi'.
>
> Can anyone think of a better solution?
>
>
>        Stefan
>
>

I don't have any ideas for a solution, but I wonder how this will
affect libraries that use the foo/bar (non-)convention, e.g. the
defvar yas/keymap in yasnippet?

-- 
Deniz Dogan