Re: [External] : Re: Lexical vs. dynamic: small examples?

[Emanuel Berg]

Stefan Monnier via Users list for the GNU Emacs text editor wrote:

> One example is the variable `pi` which holds the famous
> constant but we don't want (let ((pi (get-previous-interval
> x))) ...) to temporarily redefine `pi` to
> something unrelated.
>
> This example is obsolete, tho: you should use `float-pi`
> instead of `pi` to refer to the famous constant.

Right, but `float-pi' is defined with `defconst'.

Let's see what it says ...

  Define SYMBOL as a constant variable. This declares that
  neither programs nor users should ever change the value.
  This constancy is not actually enforced by Emacs Lisp, but
  SYMBOL is marked as a special variable so that it is never
  lexically bound.

It looks like this in float-sup.el:

  (defconst float-pi (* 4 (atan 1)) "The value of Pi (3.1415926...).")
  (with-suppressed-warnings ((lexical pi))
    (defconst pi float-pi
      "Obsolete since Emacs-23.3.  Use `float-pi' instead."))
  (internal-make-var-non-special 'pi)

So `pi' is explicitely made non-dynamic with
`internal-make-var-non-special'.

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