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fixed structure printing, added example to check-range

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This commit is contained in:
Matthias Felleisen 2014-04-05 07:11:53 -04:00
parent b82b8a6c24
commit fb34d4e76e
1 changed files with 46 additions and 3 deletions
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49
pkgs/htdp-pkgs/htdp-doc/scribblings/htdp-langs/prim-ops.rkt
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@ -444,7 +444,11 @@ In contrast, when @racket[delta] is small, the test fails:
#:eval #:eval
(mk-eval (mk-eval
(require test-engine/racket-tests) (require test-engine/racket-tests)
(define-struct roots (x sqrt) #:transparent) (define-struct roots (x sqrt)
#:transparent
#:methods gen:custom-write
[(define (write-proc x port mode)
(display `(make-roots ,(roots-x x) ,(roots-sqrt x)) port))])
(define (roots-table xs) (map (lambda (a) (make-roots a (sqrt a))) xs))) (define (roots-table xs) (map (lambda (a) (make-roots a (sqrt a))) xs)))
(check-within (roots-table (list 2.)) (check-within (roots-table (list 2.))
@ -536,8 +540,26 @@ Consider the following two examples in this context:
Checks that the value of the first @racket[expression] as that of Checks that the value of the first @racket[expression] as that of
one of the following @racket[expression]s. one of the following @racket[expression]s.
It is an error for any of @racket[expressions] @;%
to produce a function value; see note on @racket[check-expect] for details. @(begin
#reader scribble/comment-reader
(racketblock
;; [List-of X] -> X
;; pick a random element from the given list @racket[l]
(define (pick-one l)
(list-ref l (random (length l))))
))
@;%
@examples[#:eval
(mk-eval (require test-engine/racket-tests)
(define (pick-one l) (list-ref l (random (length l)))))
(check-member-of (pick-one '("a" "b" "c")) "a" "b" "c")
]
It is an error for any of @racket[expressions] to produce a function value; see
note on @racket[check-expect] for details.
} }
@defform*[#:id [check-range check-range-id] @defform*[#:id [check-range check-range-id]
@ -547,6 +569,27 @@ Consider the following two examples in this context:
between the value of the @racket[low-expression] and the between the value of the @racket[low-expression] and the
@racket[high-expression], inclusive. @racket[high-expression], inclusive.
A @racket[check-range] form is best used to delimit the possible results of
functions that compute inexact numbers:
@;%
@(begin
#reader scribble/comment-reader
(racketblock
;; [Real -> Real] Real -> Real
;; what is the slope of @racket[f] at @racket[x]?
(define (differentiate f x)
(local ((define epsilon .001)
(define left (- x epsilon))
(define right (+ x epsilon))
(define slope
(/ (- (f right) (f left))
2 epsilon)))
slope))
(check-range (differentiate sin 0) 0.99 1.00)
))
@;%
It is an error for @racket[expression], @racket[low-expression], or It is an error for @racket[expression], @racket[low-expression], or
@racket[high-expression] to produce a function value or an inexact number; @racket[high-expression] to produce a function value or an inexact number;
see note on @racket[check-expect] for details. } see note on @racket[check-expect] for details. }