4 Jan
2012
4 Jan
'12
2:39 p.m.
On Tue, Jan 3, 2012 at 3:25 PM, Ryan Davis ryan@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