[alexandria-devel] [Spam] Re: [PATCH] lazy-evaluate the default value in ENSURE-GETHASH

[Willem Broekema]

On Tue, Jan 3, 2012 at 3:25 PM, Ryan Davis <ryan at acceleration.net> wrote:
> I also recently learned about constantp and just got excited :).

Talking about constantp: it takes as arguments: form &optional environment.

Constantness can depend on the environment, e.g. if the form is (m)
and its definition is like:

(defmacro m (&environment env)
  (if (foo-p env) :constant-form (non-constant-form)))

Therefore you should always pass on environment within macros, so instead of:

(defmacro ensure-gethash (key hash-table &optional default)
  `(... ,(if (constantp default) ..)))

use:

(defmacro ensure-gethash (key hash-table &optional default &environment env)
  `(... ,(if (constantp default env) ..)))

- Willem