(shadow 'if)
(defmacro if (&rest args)
(cond ((null args) nil)
((null (cdr args)) (car args))
(t `(cond (,(car args) ,(cadr args))
(t (if ,@(cddr args)))))))
(shadow 'map)
(defun map1 (f xs)
(if (null xs)
nil
nil
nil
(cons (funcall f (car xs)) (cdr xs))))
(shadow 'some)
(defun some (test xs)
(and xs (or (funcall test (car xs)) (some test (cdr xs)))))
(defun map (f &rest xses)
(if (some #'null xses)
nil
(cons (apply f (map1 #'car xses))
(apply #'map f (map1 #'cdr xses)))))
* (map (lambda (x) (+ x 5)) '(1 2 3)) ; SBCL
(6 7 8)
OH MY GAAAAAAAAAAAAAAAAAAAAAAD IT SEEMS TO WORK
(And things can still be accessed with cl:<name> for real primitives that
require the old primitives.) That is amazing. Thank you. Common Lisp is
now much more hospitable. (There are still two namespaces, but that can be
dealt with--at worst, using binding and assignment constructs that affect
both namespaces.) Wonderful.
--John Boyle
*Science is what we understand well enough to explain to a computer. Art is
everything else we do.* --Knuth
On Thu, Oct 11, 2012 at 7:52 PM, John Cowan <[email protected]> wrote:
> John Boyle scripsit:
>
> > Can you explain further, perhaps give code that works? I've used let,
> > flet, and macrolet to rebind cl:if, and tried to run defmacro under that
> > binding, and none of them worked (in CLisp or SBCL).
>
> IF is a symbol in the CL package, and attempts to rebind or redefine
> symbols
> in that package don't work. So you need to create a symbol in some other
> package by saying (shadow 'if), which forces the current package to contain
> a separate IF symbol unrelated to CL:IF. You can then define that
> however you want.
>
> In standard Scheme there are no packages, so there is only one symbol
> named "if". However, you can rebind or redefine it as you will. In R6RS
> and R7RS, you need to exclude it when you import the base library.
>
> --
> John Cowan http://www.ccil.org/~cowan [email protected]
> Uneasy lies the head that wears the Editor's hat! --Eddie Foirbeis Climo
>
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