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