Re: Strange behavior of macro

[David Kastrup <dak@gnu.org>]

"Herbert Euler" <herberteuler@hotmail.com> writes:

> Is the following in Emacs a expected behavior of macro?
>
>    (defmacro m1 (v)
>      (let ((len (length (eval v))))
>        `(quote ,len)))
>         => m1
>
>    (m1 '(1 2 3))
>         => 3
>
>    (setq v1 '(1 2 3))
>         => (1 2 3)
>
>    (m1 v1)
>         => 3
>
>    (setq v v1)
>         => (1 2 3)
>
>    (m1 v)
>         => error: (wrong-type-argument sequencep v)

In combination with dynamic scope, yes.  m1 gets passed 'v as v, so
now v is bound to 'v and (eval v) again delivers 'v.

Evaluating a macro argument in the macro itself is often asking for
trouble.  And Elisp's scoping rules don't exactly help.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum