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docs: correct contract for mem{ber,q,v,f} and ass{oc,q,v,f}

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The list-like argument doesn't have to be a list, as long as it's a
chain of pairs to the point where an element is found.
This commit is contained in:
Matthew Flatt 2021-03-17 13:49:35 -06:00
parent e2cbd9bd73
commit f43f2f552f
1 changed files with 26 additions and 13 deletions
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39
pkgs/racket-doc/scribblings/reference/pairs.scrbl
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@ -580,24 +580,32 @@ effectively shuffles the list.}
@; ---------------------------------------- @; ----------------------------------------
@section{List Searching} @section{List Searching}
@defproc[(member [v any/c] [lst list?] @defproc[(member [v any/c] [lst (or/c list? any/c)]
[is-equal? (any/c any/c -> any/c) equal?]) [is-equal? (any/c any/c -> any/c) equal?])
(or/c list? #f)]{ (or/c #f list? any/c)]{
Locates the first element of @racket[lst] that is @racket[equal?] to Locates the first element of @racket[lst] that is @racket[equal?] to
@racket[v]. If such an element exists, the tail of @racket[lst] @racket[v]. If such an element exists, the tail of @racket[lst]
starting with that element is returned. Otherwise, the result is starting with that element is returned. Otherwise, the result is
@racket[#f]. @racket[#f].
The @racket[lst] argument need not actually be a list; @racket[lst]
must merely start with a chain of pairs until a matching element is
found. If no matching element is found, then @racket[lst] must be a
list (and not a cyclic list). The result can be a non-list in the case
that an element is found and the returned tail of @racket[lst] is a
non-list.
@mz-examples[ @mz-examples[
(member 2 (list 1 2 3 4)) (member 2 (list 1 2 3 4))
(member 9 (list 1 2 3 4)) (member 9 (list 1 2 3 4))
(member #'x (list #'x #'y) free-identifier=?) (member #'x (list #'x #'y) free-identifier=?)
(member #'a (list #'x #'y) free-identifier=?)]} (member #'a (list #'x #'y) free-identifier=?)
(member 'b '(a b . etc))]}
@defproc[(memv [v any/c] [lst list?]) @defproc[(memv [v any/c] [lst (or/c list? any/c)])
(or/c list? #f)]{ (or/c #f list? any/c)]{
Like @racket[member], but finds an element using @racket[eqv?]. Like @racket[member], but finds an element using @racket[eqv?].
@ -606,8 +614,8 @@ Like @racket[member], but finds an element using @racket[eqv?].
(memv 9 (list 1 2 3 4))]} (memv 9 (list 1 2 3 4))]}
@defproc[(memq [v any/c] [lst list?]) @defproc[(memq [v any/c] [lst (or/c list? any/c)])
(or/c list? #f)]{ (or/c #f list? any/c)]{
Like @racket[member], but finds an element using @racket[eq?]. Like @racket[member], but finds an element using @racket[eq?].
@ -616,8 +624,8 @@ Like @racket[member], but finds an element using @racket[eq?].
(memq 9 (list 1 2 3 4))]} (memq 9 (list 1 2 3 4))]}
@defproc[(memf [proc procedure?] [lst list?]) @defproc[(memf [proc procedure?] [lst (or/c list? any/c)])
(or/c list? #f)]{ (or/c #f list? any/c)]{
Like @racket[member], but finds an element using the predicate Like @racket[member], but finds an element using the predicate
@racket[proc]; an element is found when @racket[proc] applied to the @racket[proc]; an element is found when @racket[proc] applied to the
@ -642,7 +650,7 @@ tail of @racket[lst] or @racket[#f].
@defproc[(assoc [v any/c] @defproc[(assoc [v any/c]
[lst (listof pair?)] [lst (or/c (listof pair?) any/c)]
[is-equal? (any/c any/c -> any/c) equal?]) [is-equal? (any/c any/c -> any/c) equal?])
(or/c pair? #f)]{ (or/c pair? #f)]{
@ -651,6 +659,11 @@ Locates the first element of @racket[lst] whose @racket[car] is equal to
the pair (i.e., an element of @racket[lst]) is returned. Otherwise, the the pair (i.e., an element of @racket[lst]) is returned. Otherwise, the
result is @racket[#f]. result is @racket[#f].
The @racket[lst] argument need not actually be a list of pairs;
@racket[lst] must merely start with a chain of pairs contains pairs
until a matching element is found. If no matching element is found,
then @racket[lst] must be a list of pairs (and not a cyclic list).
@mz-examples[ @mz-examples[
(assoc 3 (list (list 1 2) (list 3 4) (list 5 6))) (assoc 3 (list (list 1 2) (list 3 4) (list 5 6)))
(assoc 9 (list (list 1 2) (list 3 4) (list 5 6))) (assoc 9 (list (list 1 2) (list 3 4) (list 5 6)))
@ -659,7 +672,7 @@ result is @racket[#f].
(lambda (a b) (< (abs (- a b)) 1)))]} (lambda (a b) (< (abs (- a b)) 1)))]}
@defproc[(assv [v any/c] [lst (listof pair?)]) @defproc[(assv [v any/c] [lst (or/c (listof pair?) any/c)])
(or/c pair? #f)]{ (or/c pair? #f)]{
Like @racket[assoc], but finds an element using @racket[eqv?]. Like @racket[assoc], but finds an element using @racket[eqv?].
@ -668,7 +681,7 @@ Like @racket[assoc], but finds an element using @racket[eqv?].
(assv 3 (list (list 1 2) (list 3 4) (list 5 6)))]} (assv 3 (list (list 1 2) (list 3 4) (list 5 6)))]}
@defproc[(assq [v any/c] [lst (listof pair?)]) @defproc[(assq [v any/c] [lst (or/c (listof pair?) any/c)])
(or/c pair? #f)]{ (or/c pair? #f)]{
Like @racket[assoc], but finds an element using @racket[eq?]. Like @racket[assoc], but finds an element using @racket[eq?].
@ -677,7 +690,7 @@ Like @racket[assoc], but finds an element using @racket[eq?].
(assq 'c (list (list 'a 'b) (list 'c 'd) (list 'e 'f)))]} (assq 'c (list (list 'a 'b) (list 'c 'd) (list 'e 'f)))]}
@defproc[(assf [proc procedure?] [lst (listof pair?)]) @defproc[(assf [proc procedure?] [lst (or/c (listof pair?) any/c)])
(or/c pair? #f)]{ (or/c pair? #f)]{
Like @racket[assoc], but finds an element using the predicate Like @racket[assoc], but finds an element using the predicate