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at JPR's request: modified memq to return boolean and added memq? to teaching languages

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the symmetry to member/member? suggested he is correct
This commit is contained in:
Matthias Felleisen 2012-12-30 14:16:44 -05:00
parent 05ce8bce80
commit ede0e3c625
2 changed files with 20 additions and 4 deletions
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12
collects/lang/private/beginner-funs.rkt
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@ -491,12 +491,16 @@
Evaluates the number of items on a list. Evaluates the number of items on a list.
@interaction[#:eval (bsl) x (length x)] @interaction[#:eval (bsl) x (length x)]
} }
@defproc[(memq [x any/c][l list?]) (or/c false list?)]{ @defproc[((beginner-memq memq) [x any/c][l list?]) boolean?]{
Determines whether some value is on some list if so, it produces the Determines whether some value @racket[x] is on some list @racket[l],
suffix of the list that starts with x if not, it produces false. (It using @racket[eq?] to compare @racket[x] with items on @racket[l].
compares values with the eq? predicate.)
@interaction[#:eval (bsl) x (memq (list (list 1 2 3)) x)] @interaction[#:eval (bsl) x (memq (list (list 1 2 3)) x)]
} }
@defproc[((beginner-memq? memq?) [x any/c][l list?]) boolean?]{
Determines whether some value @racket[x] is on some list @racket[l],
using @racket[eq?] to compare @racket[x] with items on @racket[l].
@interaction[#:eval (bsl) x (memq? (list (list 1 2 3)) x)]
}
@defproc[(memv [x any/c][l list?]) (or/c false list)]{ @defproc[(memv [x any/c][l list?]) (or/c false list)]{
Determines whether some value is on the list if so, it produces the Determines whether some value is on the list if so, it produces the
suffix of the list that starts with x if not, it produces false. (It suffix of the list that starts with x if not, it produces false. (It

12
collects/lang/private/teachprims.rkt
View File

@ -139,6 +139,16 @@ namespace.
(current-continuation-marks)))) (current-continuation-marks))))
(sqr a))) (sqr a)))
(define-teach beginner memq
(lambda (a b)
(check-second 'memq a b)
(not (boolean? (memq a b)))))
(define-teach beginner memq?
(lambda (a b)
(check-second 'memq? a b)
(not (boolean? (memq a b)))))
(define-teach beginner member (define-teach beginner member
(lambda (a b) (lambda (a b)
(check-second 'member a b) (check-second 'member a b)
@ -402,6 +412,8 @@ namespace.
beginner-list? beginner-list?
beginner-member beginner-member
beginner-member? beginner-member?
beginner-memq
beginner-memq?
beginner-remove beginner-remove
beginner-cons beginner-cons
beginner-car beginner-car