From Newsgroup: comp.lang.lisp

Re: newbie question

I am starting now learning common lisp.
here is a function which meant to return all elements found in list1
which dose not exists on list 2.

Try loop :

(defun not-present (x1 x2)
(loop for e in x1
when (not (member e x2)) collect e))

(not-present '(1 2 3 4 7 8 ) '( 3 4 5))
(1 2 7 8)

Gauche Scheme

(define (not-present x1 x2)
(remove (cut member <> x2) x1))

(not-present '(1 2 3 4 7 8 ) '( 3 4 5))
===>
(1 2 7 8)
--
[T]he problem is that lispniks are as cultish as any other devout group and basically fall down frothing at the mouth if they see [heterodoxy].
--- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham --- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.lisp

B. Pym wrote:

Re: newbie question

I am starting now learning common lisp.
here is a function which meant to return all elements found in list1 which dose not exists on list 2.

Try loop :

(defun not-present (x1 x2)
(loop for e in x1
when (not (member e x2)) collect e))

(not-present '(1 2 3 4 7 8 ) '( 3 4 5))
(1 2 7 8)

Gauche Scheme

(define (not-present x1 x2)
(remove (cut member <> x2) x1))

(not-present '(1 2 3 4 7 8 ) '( 3 4 5))
===>
(1 2 7 8)

Gauche Scheme

(define (not-present x1 x2)
(% remove (member _ x2) x1))

(not-present '(1 2 3 4 7 8 ) '( 3 4 5))
===>
(1 2 7 8)

Given:

;; Anaphoric macro to abbreviate lambdas for higher-order functions.
;; Uses "_" for 1 argument;
;; uses "A:" and "B:" and so on for 2 or more arguments.
;; This version works under both Gauche Scheme
;; and Racket. Racket needs:
;; (require compatibility/defmacro)
;;
(define-macro %
(case-lambda
((func expr List) `(,func (lambda(_) ,expr) ,List))
((func expr . more)
(let* ((n 64)
(nums (map (lambda _ (set! n (+ 1 n)) n) more))
(vnames
(map (lambda(n)
(string->symbol (string (integer->char n) #\:)))
nums)))
`(,func (lambda ,vnames ,expr) ,@more)))))
--
[T]he problem is that lispniks are as cultish as any other devout group and basically fall down frothing at the mouth if they see [heterodoxy].
--- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham --- Synchronet 3.21a-Linux NewsLink 1.2

From Newsgroup: comp.lang.lisp

Frode Vatvedt Fjeld wrote:

"dvlfrnd" <ires...@yahoo.com> writes:

say there's a list of even length
(a b c d e f ......)

how do i turn this into
((a b) (c d) (e f)....)

The mapping idiom doesn't work so well here, since that's all about transforming each element individually, whereas here you process
elements two by two (or the list as such in steps of two).

I think this is the most natural solution in Common Lisp:

(loop for (x y) on list by #'cddr collect (list x y))

Gauche Scheme

"!" is similar to "do".

(! (r cons (list x y)
(x y) :on '(a b c d e f) :by cddr)
@)

===>
((a b) (c d) (e f))

Given:

(define-syntax !-aux
(syntax-rules (<> @ @@ + - : cons append :meld
cdr :in :across :along
:on :by :pop-or-nothing
:if :if-else ! :also? :also :to
:till :always
:let := )
[(_ specs seen lets @)
(!-aux specs seen lets #f @) ]
[(_ (:let id val z ...) seen (lets ...) stuff ...)
(!-aux (z ...) seen (lets ... (id val)) stuff ...) ]
[(_ (:= id val z ...) stuff ...)
(!-aux (:let id #f dummy #f (set! id val) z ...) stuff ...) ]
;;
[(_ (:also? bool op x z ...) (seen ... (v i update)) stuff ...)
(!-aux (z ...)
(seen ... (v i (if bool (op x update) update)))
stuff ...) ]
[(_ (:also op x z ...) stuff ...)
(!-aux (:also? #t op x z ...) stuff ...) ]
;;
[(_ ((:pop-or-nothing x xs nil) z ...) stuff ...)
(!-aux (x (if (pair? xs)(pop! xs) nil) <> z ...) stuff ...) ]
;;
;;
[(_ (:always expr z ...) seen lets bool)
(!-aux (ok #t expr
:till (not ok)
z ...)
seen lets bool ok
) ]
[(_ (:always expr z ...) stuff ...)
(!-aux " * * * Bad usage of :always in !") ]
[(_ (:till expr z ...) seen lets #f stuff ...)
(!-aux (z ...) seen lets expr stuff ...) ]
[(_ (:till expr z ...) seen lets bool stuff ...)
(!-aux (z ...) seen lets (or expr bool) stuff ...) ]
;;
[(_ (:if bool z ...) (seen ... (v i u)) stuff ...)
(!-aux (z ...)
(seen ... (v i (if bool u v))) stuff ...) ]
;;
[(_ (:if-else bool z ...) (seen ... (a b c)(d e f)) stuff ...)
(!-aux (:let yes #f z ...)
(seen ... (a b (begin (set! yes bool) (if yes c a)))
(d e (if (not yes) f d))) stuff ...) ]
;;
[(_ ((a b ...) :on lst :by kdr z ...) stuff ...)
(!-aux (:let xs lst
:let ys #f
exhausted (null? xs) <>
dummy (begin (set! ys xs)
(when (pair? xs) (set! xs (kdr xs)))) <>
(:pop-or-nothing a ys #f)
(:pop-or-nothing b ys #f) ...
:till exhausted
z ...) stuff ...) ]
[(_ ((a b ...) :on lst z ...) stuff ...)
(!-aux ((a b ...) :on lst :by cdr z ...) stuff ...) ]
;;
[(_ (x :in lst z ...) stuff ...)
(!-aux (:let xs lst
x (if (pair? xs)(pop! xs) !-aux) <>
:till (eq? x !-aux)
z ...) stuff ...) ]
;;
[(_ (x :across vec z ...) stuff ...)
(!-aux (:let v vec :let i 0
x (if (< i (vector-length v))
(begin0 (vector-ref v i) (inc! i))
!-aux) <>
:till (eq? x !-aux)
z ...) stuff ...) ]
[(_ (ch :along str z ...) stuff ...)
(!-aux (:let s str :let i 0
ch (and (< i (string-length s))
(begin0 (string-ref s i) (inc! i))) <>
:till (not ch)
z ...)
stuff ...) ]
[(_ (a b <> z ...) stuff ...)
(!-aux (a b b z ...) stuff ...) ]
;;
[(_ (a b + z ...) stuff ...)
(!-aux (a b (+ 1 a) z ...) stuff ...) ]
[(_ (a + n z ...) stuff ...)
(!-aux (a 0 (+ n a) z ...) stuff ...) ]
[(_ (a b - z ...) stuff ...)
(!-aux (a b (- a 1) z ...) stuff ...) ]
[(_ (n lo inc :to hi z ...) stuff ...)
(!-aux (:let step inc :let high hi
n lo (+ n step)
:till (> n high)
z ...) stuff ...) ]
[(_ (n lo :to hi z ...) stuff ...)
(!-aux (n lo 1 :to hi z ...) stuff ...) ]
;;
[(_ (v init : kons u z ...) stuff ...)
(!-aux (v init (kons u v) z ...) stuff ...) ]
;;
[(_ (a cons b z ...) stuff ...)
(!-aux (a '() : cons b z ...) stuff ...) ]
[(_ (a append b z ...) stuff ...)
(!-aux (a '() : append b z ...) stuff ...) ]
[(_ (a :meld b z ...) stuff ...)
(!-aux (a '()
(if (pair? b) (append (reverse b) a)
(cons b a))
z ...) stuff ...) ]
;;
[(_ (a b cdr z ...) stuff ...)
(!-aux (a b (cdr a) z ...) stuff ...) ]
[(_ (a b c z ...) (seen ...) stuff ...)
(!-aux (z ...) (seen ... (a b c)) stuff ...) ]
[(_ (a b) (seen ...) stuff ...)
(!-aux () (seen ... (a b)) stuff ...) ]
[(_ (a) (seen ...) stuff ...)
(!-aux () (seen ... (a '())) stuff ...) ]
;; Default action is print first variable.
[(_ () ((a b c) z ...) lets bool !)
(!-aux () ((a b c) z ...) lets bool ! print a) ]
;; (!-aux () ((a b c) z ...) lets bool ! begin (print a)(sys-sleep 1)) ]
[(_ () seen lets bool ! action ...)
(!-aux () seen lets bool #t (action ...)) ]
;; If result not specified, pick one.
[(_ () ((a b c) z ...) lets bool)
(!-aux () ((a b c) z ...) lets bool a) ]
[(_ () ((a b c) z ...) lets bool @)
(!-aux () ((a b c) z ...) lets bool (reverse a)) ]
[(_ () seen lets bool @ result stuff ...)
(!-aux () seen lets bool (reverse result) stuff ...) ]
;;
[(_ () seen lets bool @@ (what x ...) stuff ...)
(!-aux () seen lets bool (what (reverse x) ...) stuff ...) ]
[(_ () seen lets bool (what @ x z ...) stuff ...)
(!-aux () seen lets bool (what (reverse x) z ...) stuff ...) ]
[(_ () seen lets bool (what x @ y z ...) stuff ...)
(!-aux () seen lets bool (what x (reverse y) z ...) stuff ...) ]
;;
[(_ () ((a b c) z ...) lets 0 stuff ...)
(!-aux () ((a b c) z ...) lets (= 0 a) stuff ...) ]
[(_ () seen lets bool result stuff ...)
(let lets (do seen (bool result) stuff ...)) ]
))
(define-syntax !
(syntax-rules ()
[(_ specs bool stuff ...)
(!-aux specs () () bool stuff ...) ]
[(_ specs) (! specs #f) ]
))
--
[T]he problem is that lispniks are as cultish as any other devout group and basically fall down frothing at the mouth if they see [heterodoxy].
--- Kenny Tilton
The good news is, it's not Lisp that sucks, but Common Lisp. --- Paul Graham --- Synchronet 3.21a-Linux NewsLink 1.2