A pair (sometimes called a dotted pair) is a record structure with two fields called the car and cdr fields (for historical reasons). Pairs are created by the procedure cons. The car and cdr fields are accessed by the procedures car and cdr.
Pairs are used primarily to represent lists. A list can be defined recursively as either the empty list or a pair whose car is the first element of list and cdr is the remainder of list (which either the empty list or a pair whose ....).
cons, pair?, car, cdr,
list, make-list, list-copy, #null, null?, cons*, list?,
caar, cadr, cdar, cddr,
caaar, caadr, cadar, caddr, cdaar, cdadr, cddar, cdddr,
caaaar, caaadr, caadar, caaddr, cadaar, cadadr, caddar, cadddr, cdaaar, cdaadr, cdadar, cdaddr, cddaar, cddadr, cdddar, cddddr,
length, list-ref (lref), list-tail,
repeat, iota, lrange, append, reverse,
take, drop,
memq, memv, member, assq, assv, assoc,
map, fold, foldr,
first, second, third, fourth, fifth,
sixth, seventh, eighth, ninth, tenth
(cons obj1 obj2), primop
Returns a newly allocated pair whose car is obj1 and whose cdr is obj2.
The pair is guaranteed to be different (in the sense of eq? and eqv?) from every existing object.
(cons 1 2) ==> '(1 . 2)
(cons 'a 3) ==> '(a . 3)
(cons 1 '()) ==> '(1)
(cons '() 1) ==> '(() . 1)
(cons '(a) '(b c d)) ==> '((a) b c d)
(cons 'a '(b c)) ==> '(a b c)
(cons '(a b) 'c) ==> '((a b) . c)(pair? obj), procedure
Returns #true if obj is a pair, otherwise returns #false.
(pair? 1) ==> #false
(pair? '(a . b)) ==> #true
(pair? '(a b c)) ==> #true
(pair? '()) ==> #false
(pair? #(a b)) ==> #false
(pair? '{a b}) ==> #false
(pair? #true) ==> #false
(pair? 17/121) ==> #false(car pair), primop
Returns the contents of the car field of pair. Note that it is an error to take the car of the not a pair.
(car (cons 1 2)) ==> 1
(car (cons 'a 3)) ==> 'a
(car (cons 1 '())) ==> 1
(car (cons '() 1)) ==> '()
(car (cons '(a) '(b c d))) ==> '(a)
(car (cons "a" '(b c))) ==> "a"
(car (cons '(a b) 'c)) ==> '(a b)
(car '(1 2 3 4 5)) ==> 1(cdr pair), primop
Returns the contents of the cdr field of pair. Note that it is an error to take the cdr of the empty list.
(cdr (cons 1 2)) ==> 2
(cdr (cons 'a 3)) ==> 3
(cdr (cons 1 '())) ==> '()
(cdr (cons '() 1)) ==> 1
(cdr (cons '(a) '(b c d))) ==> '(b c d)
(cdr (cons "a" '(b c))) ==> '(b c)
(cdr (cons '(a b) 'c)) ==> 'c
(cdr '(1 2 3 4 5)) ==> '(2 3 4 5)(list obj ...), macro
Returns a newly allocated list of its arguments.
(list 1 2 3 4 5 6 7) ==> '(1 2 3 4 5 6 7)
(list 1 2 3) === (cons 1 (cons 2 (cons 3 #null)))
(list 'a (+ 3 4) 'c) ==> '(a 7 c)
(list) ==> '()
(list (list 1 2) (list 3 4)) ==> '((1 2) (3 4))(make-list k), procedure
(make-list k fill), procedure
Returns a newly allocated list of k elements. If a second argument is given, then each element is initialized to fill. Otherwise the initial contents of each element is #false.
(make-list 4) ==> '(#false #false #false #false)
(make-list 7 3) ==> '(3 3 3 3 3 3 3)
(make-list 0) ==> '()(list-copy obj), procedure
Returns a newly allocated shallow copy of the given obj if it is a list.
Only the pairs themselves are copied; the cars of the result are the same (in the sense of eqv?) as the cars of list.
(list-copy '()) ==> '()
(list-copy '(1 2 (3) 4)) ==> '(1 2 (3) 4)
(let ((l '(1 2)))
(eq? (list-copy l) l)) ==> #false
(let*((x '("a" ("b" "c") "d"))
(y (list-copy x)))
(eq? (lref x 1) (lref y 1))) ==> #true ; ("b" "c")#null, constant
The empty list. Mainly known as '().
null (deprecated, but still widely used) is the same as #null.
#n is a one more synonym for #null.
#null ==> '()
null ==> '() ; `null` is depraceted
#n ==> #null(null? obj), procedure
Returns #true if obj is the empty list, otherwise returns #false.
(null? 1) ==> #false
(null? '(a . b)) ==> #false
(null? '()) ==> #true
(null? #null) ==> #true
(null? null) ==> #true ; `null` is deprecated
(null? (cdr '(1))) ==> #true
(null? #false) ==> #false(cons* obj ...), macro
Returns a newly allocated improper(!) list of its arguments.
(cons* 1 2) ==> '(1 . 2)
(cons* 'a (+ 3 4) 'c) ==> '(a 7 . c)
(cons* 1) ==> 1(list? obj), procedure
Returns #true if obj is a proper list, otherwise returns #false.
(list? '(1 . 2)) ==> #false
(list? '(1 2 3)) ==> #true
(list? '()) ==> #true
(list? #false) ==> #false
(list? (cons 1 (cons 2 '()))) ==> #true
(list? (cons 1 2)) ==> #false
(list? (cons 1 #null)) ==> #true
(list? (cons* 1 2 3)) ==> #false(caar list), procedure
(cadr list), procedure
(cdar list), procedure
(cddr list), procedure
(caaar list), procedure
(caadr list), procedure
...
(cddar list), procedure
(cdddr list), procedure
(caaaar list), procedure, (scheme cxr)
(caaadr list), procedure, (scheme cxr)
...
(cdddar list), procedure, (scheme cxr)
(cddddr list), procedure, (scheme cxr)
caar === (lambda (x) (car (car x)))
cadr === (lambda (x) (car (cdr x)))
cdar === (lambda (x) (cdr (car x)))
cddr === (lambda (x) (cdr (cdr x)))
(cddadr '(1 (2 3 4 5) 6)) ==> '(4 5)
(cadadr '(1 (2 3 4 5) 6)) ==> 3(length list), procedure
Returns the length of list.
(length '(a b c)) ==> 3
(length '(a (b) (c d e))) ==> 3
(length '()) ==> 0(list-ref list k), procedure
lref is the same as list-ref, widely used
Returns the kth element of list.
(list-ref '(a b c) 0) ==> 'a
(list-ref '(a b c) 8) ==> #false
(list-ref '(a b c d) 2) ==> 'c(list-tail list k), procedure
Returns the sublist of list obtained by omitting the first k elements.
(list-tail '(1 2 3 4) 2) ==> '(3 4)
(list-tail '(1 2 3) 0) ==> '(1 2 3)(repeat fill k), procedure
Returns a newly allocated list of k elements, each is initialized to fill.
(repeat 7 3) ==> '(7 7 7)
(repeat "me" 6) ==> '("me" "me" "me" "me" "me" "me")(iota count), procedure
(iota count start), procedure
(iota count start step), procedure
Returns a newly allocated list with sequence of count numbers from start with step step. The default value of start is a 0. The default values of step is a 1.
(iota 12) ==> '(0 1 2 3 4 5 6 7 8 9 10 11)
(iota 5 -3) ==> '(-3 -2 -1 0 1)
(iota 3 10 1000) ==> '(10 1010 2010)(lrange from step to), procedure
Returns a newly allocated list with sequence of numbers from from to to with step step.
(lrange 0 1 10) ==> '(0 1 2 3 4 5 6 7 8 9)
(lrange 1 3 10) ==> '(1 4 7)
(lrange 5 -1 0) ==> '(5 4 3 2 1)(append list ...), procedure
Returns a list consisting of the elements of the first list followed by the elements of the other lists.
(append) ==> '()
(append '(x) '(y)) ==> '(x y)
(append '(a) '(b c d)) ==> '(a b c d)
(append '(a (b)) '((c))) ==> '(a (b) (c))
(append '(a b) '(c . d)) ==> '(a b c . d)
(append '() 'a) ==> 'a
(append '(1 2 3)) ==> '(1 2 3)
(append '(1) '(2) '(3 (4)) '(5)) ==> '(1 2 3 (4) 5)
(append '(1 2 3) 4) ==> '(1 2 3 . 4)(reverse list), procedure
Returns a newly allocated list consisting of the elements of list in reverse order.
(reverse '(a b c)) ==> '(c b a)
(reverse '(a (b c) d (e (f)))) ==> '((e (f)) d (b c) a)(take list count), procedure
Returns list with first count elements of list, if count less or equal to list length. Otherwise returns just a copy of a list.
(take '(1 2 3 4 5) 3) ==> '(1 2 3)
(take '(1 2 3) 0) ==> '()
(take '(1 2) 777) ==> '(1 2)(drop list count), procedure
Returns list with last count elements of list, if count less or equal to list length. Otherwise returns empty list.
(drop '(1 2 3 4 5) 3) ==> '(4 5)
(drop '(1 2 3) 0) ==> '(1 2 3)
(drop '(1 2) 777) ==> '()(memq obj list), procedure
Returns the first sublist of list whose car is obj, where the sublists of list are the non-empty lists returned by (list-tail list k) for k less than the length of list, otherwise returns #f.
The memq procedure uses eq? to compare obj with the elements of list.
(memq 'a '(a b c)) ==> '(a b c)
(memq 'b '(a b c)) ==> '(b c)
(memq 'a '(b c d)) ==> #false
(memq "b" '("a" "b" "c")) ==> #false
(memq '(a) '(b (a) c)) ==> #false
; memq is not working for long numbers:
(memq 1000000000000000000000
'(100 1000000000000000000000 102)) ==> #false
; but working for short:
(memq 101 '(100 101 102)) ==> '(101 102)(memv obj list), procedure
Returns the first sublist of list whose car is obj, where the sublists of list are the non-empty lists returned by (list-tail list k) for k less than the length of list, otherwise returns #f.
The memv procedure uses eqv? to compare obj with the elements of list.
(memv 'a '(a b c)) ==> '(a b c)
(memv 'b '(a b c)) ==> '(b c)
(memv 'a '(b c d)) ==> #false
(memv "b" '("a" "b" "c")) ==> #false
(memv '(a) '(b (a) c)) ==> #false
; memv is working for any numbers:
(memv 1000000000000000000000
'(100 1000000000000000000000 102)) ==> '(1000000000000000000000 102)
(memv 101 '(100 101 102)) ==> '(101 102)(member obj list), procedure
(member obj list compare), procedure
Returns the first sublist of list whose car is obj, where the sublists of list are the non-empty lists returned by (list-tail list k) for k less than the length of list, otherwise returns #f.
The member procedure uses compare if given, and equal? otherwise, to compare obj with the elements of list.
(member 'a '(a b c)) ==> '(a b c)
(member 'b '(a b c)) ==> '(b c)
(member 'a '(b c d)) ==> #false
(member "b" '("a" "b" "c")) ==> '("b" "c")
(member '(a) '(b (a) c)) ==> '((a) c)
(member 101 '(100 101 102)) ==> '(101 102)
(member 1000000000000000000000
'(100 1000000000000000000000 102)) ==> '(1000000000000000000000 102)
(member "B" '("a" "b" "c")) ==> #false
(member "B" '("a" "b" "c") string-ci=?) ==> '("b" "c")(assq obj alist), procedure
Returns the first pair in alist whose car field is obj, otherwise returns #f.
The assq procedure uses eq? to compare obj with the car fields of the pairs in alist.
(assq 'a '((a 1) (b 2) (c 3))) ==> '(a 1)
(assq 'b '((a 1) (b 2) (c 3))) ==> '(b 2)
(assq 'd '((a 1) (b 2) (c 3))) ==> #false
(assq "b" '(("a" 1) ("b" 2) ("c" 3))) ==> #false
(assq '(b) '(((a) 1) ((b) 2) ((c) 3))) ==> #false
; assq is not working for long numbers:
(assq 1000000000000000000000
'((2 3) (1000000000000000000000 101) (102 103))) ==> #false
; but working for short:
(assq 5 '((2 3) (5 7) (11 13))) ==> '(5 7)(assv obj alist), procedure
Returns the first pair in alist whose car field is obj, otherwise returns #f.
The assv procedure uses eqv? to compare obj with the car fields of the pairs in alist.
(assv 'a '((a 1) (b 2) (c 3))) ==> '(a 1)
(assv 'b '((a 1) (b 2) (c 3))) ==> '(b 2)
(assv 'd '((a 1) (b 2) (c 3))) ==> #false
(assv "b" '(("a" 1) ("b" 2) ("c" 3))) ==> #false
(assv '(b) '(((a) 1) ((b) 2) ((c) 3))) ==> #false
; assv is working for any numbers:
(assv 1000000000000000000000
'((2 3) (1000000000000000000000 101) (102 103))) ==> '(1000000000000000000000 101)
(assv 5 '((2 3) (5 7) (11 13))) ==> '(5 7)(assoc obj alist), procedure
(assoc obj alist compare), procedure
Returns the first pair in alist whose car field is obj, otherwise returns #f.
The assoc procedure uses compare if given, and equal? otherwise, to compare obj with the elements of list.
(assoc 'a '((a 1) (b 2) (c 3))) ==> '(a 1)
(assoc 'b '((a 1) (b 2) (c 3))) ==> '(b 2)
(assoc 'd '((a 1) (b 2) (c 3))) ==> #false
(assoc "b" '(("a" 1) ("b" 2) ("c" 3))) ==> '("b" 2)
(assoc '(b) '(((a) 1) ((b) 2) ((c) 3))) ==> '((b) 2)
(assoc 5 '((2 3) (5 7) (11 13))) ==> '(5 7)
(assoc 1000000000000000000000 '((2 3) (1000000000000000000000 101) (102 103))) ==> '(1000000000000000000000 101)
(assoc "B" '(("a" 1) ("b" 2) ("c" 3))) ==> #false
(assoc "B" '(("a" 1) ("b" 2) ("c" 3)) string-ci=?) ==> '("b" 2)(map handler list ...), procedure
The map function uses the per-element results to create a new list.
(map - '(1 2 3)) ==> '(-1 -2 -3)
(map sqrt '(1 4 9 16)) ==> '(1 2 3 4)
(map (lambda (n i)
((if (even? i) + -) n))
'(1 3 5 7 9)
'(1 2 3 4 5)) ==> '(-1 3 -5 7 -9)
(map (lambda (n) (/ 1 n))
(iota 5 1 2)) ==> '(1 1/3 1/5 1/7 1/9)
(map (lambda (i p)
(string-append i p))
'("peanuts" "popcorn" "crackerjack")
'("!" "?" "^")) ==> '("peanuts!" "popcorn?" "crackerjack^")
(map car '(
(1 . 2) (3 . 4) (5 . 6))) ==> '(1 3 5)(fold handler state list ...), procedure
Combine the elements of list(s) from left to right.
(fold + 0 '(1 2 3)) ==> 6
(fold + 7 '(1 2 3)) ==> 13
(fold - 7 '(1 2 3)) ==> 1
(fold cons 3 '(5 6 7)) ==> '(((3 . 5) . 6) . 7)
(fold put {} '(x y z)
'(4 5 6)) ==> { 'x 4 'y 5 'z 6 }
(fold (lambda (f x)
(min f x))
100
'(6 7 8 4 7)) ==> 4
(fold (lambda (f x y)
(string-append f "/" x y))
"X"
'("a" "b" "c" "d")
'("1" "2" "3" "4")) ==> "X/a1/b2/c3/d4"
; Leibniz formula for Pi,
; 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ...
> (let ((N 10000))
(define (sign n)
(if (zero? (mod n 2)) + -))
(fold (lambda (f x i)
((sign i) f (/ #i4 x)))
#i4
(iota N 3 2)
(iota N 1)))
3.14169264(foldr handler state list ...), procedure
Combine the elements of list(s) from right to left.
(foldr + 0 '(1 2 3)) ==> 6
(foldr + 7 '(1 2 3)) ==> 13
(foldr - 7 '(1 2 3)) ==> -5
(foldr cons 3 '(5 6 7)) ==> '(5 6 7 . 3)
(foldr - 9) ==> 9
(foldr - 9 '(1 2)) ; === (- 1 (- 2 9))
==> 8
(foldr - 9 '(1 2) '(3 4)) ; === (- 1 3 (- 2 4 9))
==> 9
(foldr - 9 '(1 2) '(3 4) '(5 6)) ; === (- 1 3 5 (- 2 4 6 9))
==> 10
(foldr - 9 '(1 2) '(3 4) '(5 6) '(7 8)) ; === (- 1 3 5 7 (- 2 4 6 8 9))
==> 11
; Please note that the order of variables in the lambda differs than in fold!
(foldr (lambda (x f)
(min f x))
100
'(6 7 8 4 7)) ==> 4
(foldr (lambda (x y f)
(string-append f "/" x y))
"X"
'("a" "b" "c" "d")
'("1" "2" "3" "4")) ==> "X/d4/c3/b2/a1"Ol provides limited support for non-functional (in sense of paradigm) features. Please only use them if you know what you are doing! This can lead to unexpected behavior of your program.
(set-car! pair obj), procedure
Stores obj in the car field of pair. Obj must be enum, symbol, or constant.
(let ((x '(1 . 2)))
(set-car! x 8)
x) ==> '(8 . 2)
(let ((y (cons 'a 'b)))
(set-car! y 'xxx)
y) ==> '(xxx . b)
(let ((z '(a . #f)))
(set-car! z #t)
z) ==> '(#true . #false)(set-cdr! pair obj), procedure
Stores obj in the cdr field of pair. Obj must be enum, symbol, or constant.
(let ((x '(1 . 2)))
(set-cdr! x 8)
x) ==> '(1 . 8)
(let ((y (cons 'a 'b)))
(set-cdr! y 'xxx)
y) ==> '(a . xxx)
(let ((z '(a . #f)))
(set-cdr! z #t)
z) ==> '(a . #true)(list-set! list k obj), procedure
Stores obj in element k of list. Obj must be enum, symbol, or constant.
(let ((me '(1 2 3 4)))
(list-set! me 2 77)
me) ==> '(1 2 77 4)(first l), procedure, (srfi 1) library
Returns first element of list l.
(first '(1 2 3 4 5 6 7 8 9 10 11)) ==> 1(second l), procedure, (srfi 1) library
Returns second element of list l.
(second '(1 2 3 4 5 6 7 8 9 10 11)) ==> 2(third l), procedure, (srfi 1) library
Returns third element of list l.
(third '(1 2 3 4 5 6 7 8 9 10 11)) ==> 3(fourth l), procedure, (srfi 1) library
Returns fourth element of list l.
(fourth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 4(fifth l), procedure, (srfi 1) library
Returns fifth element of list l.
(fifth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 5(sixth l), procedure, (srfi 1) library
Returns sixth element of list l.
(sixth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 6(seventh l), procedure, (srfi 1) library
Returns seventh element of list l.
(seventh '(1 2 3 4 5 6 7 8 9 10 11)) ==> 7(eighth l), procedure, (srfi 1) library
Returns eighth element of list l.
(eighth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 8(ninth l), procedure, (srfi 1) library
Returns ninth element of list l.
(ninth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 9(tenth l), procedure, (srfi 1) library
Returns tenth element of list l.
(tenth '(1 2 3 4 5 6 7 8 9 10 11)) ==> 10