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Isn't it possible to treat functions in Scheme as any other list?
Basically, what I want do to is something like this:
(define (foo) "hello")
(cdr foo) ; or similar, should return the list ((foo) "hello")
I've found a similar discussion about this, and I feel a bit disappointed if this is not possible with Scheme. If so, why is this impossible? Is it possible in other lisps?
EDIT: Changed (cdr 'foo) to (cdr foo) -- it was misleading. I'm asking, why can't I access a function as a list?
460
The length of a list is the number of elements, which is the same as the number of pairs. The empty list is a special object of its own type (it is not a pair); it has no elements and its length is zero.
Scheme provides a procedure, null? to check whether a value is (a pointer to) the empty list, i.e., a null pointer. For example, (null? foo) returns #t if the value of the variable foo is the empty list, and #f otherwise.
The append function joins two lists together to make one. The append function is built into Scheme. It concatenates two lists, that is to say, given two lists list1 and list2 it produces a new list which starts with the same elements as list1 and finishes with those of list2 .
The other constructor, cons , is used when you already have a list and you want to add one new element. Cons takes two arguments, an element and a list (in that order), and returns a new list whose car is the first argument and whose cdr is the second.
I have often wanted to be able to do the same thing csl. Below is a quick example of how you could go about doing this in mzscheme.
DrScheme 4.2
(module qdefine mzscheme
(provide ;(all-from-except mzscheme let)
(rename define olddefine)
(rename quote-define define)
(rename quote-cdr cdr)
(rename quote-car car))
(define define-list '())
(define define-list-add
(lambda (key value)
(set! define-list (cons `(,key ,value) define-list))))
(define-syntax quote-define
(syntax-rules ()
((_ (pro-name args ...) body ...)
(begin
(define (pro-name args ...) body ...)
(define-list-add pro-name '((pro-name args ...) body ...))))
((_ pro-name pro) (begin
(define pro-name pro)
(define-list-add pro-name 'pro)))
))
(define quote-cdr (lambda (lst)
(if (procedure? lst)
(cdr (cadr (assoc lst define-list)))
(cdr lst))))
(define quote-car (lambda (lst)
(if (procedure? lst)
(car (cadr (assoc lst define-list)))
(car lst))))
)
(require 'qdefine)
(define testfunc (lambda (args) args))
(cdr testfunc)
(car testfunc)
(define (testfunc2 test) 'blah)
(cdr testfunc2)
(car testfunc2)
(define testlist '(1 2 3 4 5 6 'a))
(cdr testlist)
(car testlist)
Outputs:
((args) args)
lambda
('blah)
(testfunc2 test)
(2 3 4 5 6 'a)
1
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