4 ms·
I never found the funcall argument terribly convincing, because there is no reason it couldn't be much more concise. And it allows you to avoid silly variable n
by patrec 10y ago
I never found the funcall argument terribly convincing, because there is no reason it couldn't be much more concise. And it allows you to avoid silly variable names like lst or fst.
In Common lisp to refer to a function as a variable you do (function f) or as (read-table) syntactic sugar #'f. You could easily use destructuring to write HOFs without funcall.
So instead of requiring people to write
(defun bad-map (f list)
"Maps function `f' over `list', inefficiently."
(when list (cons (funcall #'f (first list) (bad-map f (rest list)))))
(bad-map #'- '(1 2 3))
A hypothetical lisp-2 could just as well allow destructuring like this:
(defun bad-map (#'f list)
"Maps function `f' over `list', inefficiently."
(when list (cons (f (first list) (bad-map #'f (rest list)))))
(bad-map #'- '(1 2 3))
The fact that higher order functions stick out a bit by the extra #' is not necessarily a bad thing IMO; it helps when reading unfamiliar code to know immediately what arguments are functions and which ones are just plain objects.
- lispm 10y agoIn Common Lisp in your first example it's not (funcall #'f (first list) ...) but (funcall f (first list)) ... f is already a function object. We could write a macro for that or a new version of defun. Here just a macro lisp1fy: (defmacro lisp2fy ((&rest calls) &body body) `(flet (,@(loop for (f . args) in calls collect `(,f ,args (funcall ,f ,@args)))) (declare (inline ,@(loop for (f . nil) in calls collect f))) ,@body)) (defun bad-map (f list) "Maps function `f' over `list', inefficiently." (lisp2fy ((f a)) (when list (cons (f (first list)) (bad-map f (rest list))))))
- patrec 10y agoYeah, braino -- thanks. A custom binding form would be another way to do it, but I'd prefer the pseudo-destructuring -- cleaner and more concise. I'd hope a new lisp-2 dialect would come with better destructuring support for defun and binding forms anyway (destructuring-bind, multiple-value-bind and flet could all be subsumed by let if (values ...) (function ...) where valid left hand patterns).