Re: Multiple arguments to mapcar?

Pascal Costanza wrote:

Johan wrote:

I want to map over a list, but to treat the first object differently
from the rest. My previous experience with Lisp was Interlisp, which
has dynamic binding. In Interlisp I could code my problem similar to
this:
>
(defun foo ()
  (let ((first-time t))
    (mapcar #'bar '(1 2))))
>
(defun bar (n)
  (cond
    (first-time
     (setf first-time nil)
     (+ n 1))
    (t (+ n 2))))
>
and (foo) would return (2 4). This doesn't work with lexical binding,
and I don't want to make first-time a global variable. What is the
best design pattern in Common Lisp?

 
(loop for n in '(1 2)
       for x = (+ n 1) then (+ n 2)
       collect x)

Gauche Scheme

(use gauche.parameter)

(define first-time (make-parameter 'unset))

(define (foo)
  (parameterize ((first-time #t))
    (map bar '(400 500 600))))

(define (bar n)
  (cond
    ((first-time)
     (first-time #f)
     (+ n 1))
    (#t (+ n 2))))

gosh> (foo)
(401 502 602)
gosh> (first-time)
unset