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(defun hungry-and (x &rest y)
(format t "arguments: ~a~&" x) ; but the function will stop checking them
; once it sees first argument that evaluates to nil
(when x (when y (apply 'hungry-and y))))
(hungry-and :foo :bar 42 t nil "string") ; arguments are evaluated hereCode: Select all
(defun my-and (&rest args)
(cond ((not args)
;; There are no arguments, default to true
t )
(t (and (car args) (apply #'my-and (cdr args)))) ))If you just want a two-argument version:yesimthetaxman wrote:I am trying to write a simple boolean AND function that uses eager/strict evaluation. That is, I want both arguments to the AND function to be evaluated. I am able to write a function to simulate this using IF statements, but it is long, I am wondering if anyone has any ideas how to write a shorter, more elegant version that evaluates the two arguements and then AND's them...
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(defun my-and (x y) (and x y))
I didn't test it, but it seems your code is a bit wrong because it will always return nil. For instance, with only one argument, when X is true, it will see that Y is empty and return nil.wvxvw wrote:Let's see if it helps, I'm not exactly sure where do you want to evaluate arguments, but I assumed that you didn't want to continue checking the arguments after you are sure about the result:Code: Select all
(defun hungry-and (x &rest y) (format t "arguments: ~a~&" x) ; but the function will stop checking them ; once it sees first argument that evaluates to nil (when x (when y (apply 'hungry-and y)))) (hungry-and :foo :bar 42 t nil "string") ; arguments are evaluated here
Well...
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(defun hungry-and (x &rest y)
(format t "arguments: ~a~&" x) ; but the function will stop checking them
; once it sees first argument that evaluates to nil
(when x (every 'or y)))Code: Select all
(defun hungry-and (&rest args) (every #'identity args))That won't work either, or is not a function.wvxvw wrote:Oh, sorry, it wasn't just a bit wrong, it was a whole lot wrongA fixed version. Although, I must note that smithzv would also be wrong when called with empty list for example.Code: Select all
(defun hungry-and (x &rest y) (format t "arguments: ~a~&" x) ; but the function will stop checking them ; once it sees first argument that evaluates to nil (when x (every 'or y)))
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(define-compiler-macro hungry-and (&rest args)
(let ((syms (loop repeat (length args) collect (gensym))))
`(let ,(mapcar #'list syms args)
(and ,@syms))))
). except for, as you quite righteously noted it won't work for empty list (and I did say I thought that the original 'and must take at least one argument). So, that is, of course my mistake. And well, OP wanted a function...