; TASK-1
; Length is a Number.
; interp. length of a letter in cm.
; Width is a Number.
; interp. width of a letter in cm.
; Height is a number.
; interp. height of a letter in cm.
; Weight is a Number.
; interp. weight of a letter in g.
; Format is one of:
; - "Standard"
; - "Kompakt"
; - "Gross"
; - "Maxi"
; interp. the products offered by Deutsche Post
(define (function-1 Format)
(cond
[(string=? "Standard" Format) ...]
[(string=? "Kompakt" Format) ...]
[(string=? "Gross" Format) ...]
[(string=? "Maxi" Format) ...]
[else ...]))
; MaybeFormat is one of:
; - Format
; - #false
; interp. the best Format choice, or #false if no Format would work
(define-struct MaybeFormat (Format boolean))
; A MaybeFormat is a structure: (make-MaybeFormat Format boolean)
; interp. either a Format or #false
; MaybeFormat -> String or boolean
; decides whether it's a Format or a boolean (#false)
(define (function-2 MaybeFormat)
(cond
[(MaybeFormat? MaybeFormat) ...]
[else ...]))
; TASK-2
; Length Width Height Weight -> MaybeFormat
; find the cheapest format to send something
(check-expect (cheapest-format 14 9 0.5 20) "Standard")
(check-expect (cheapest-format 23.5 12.5 0.5 20) "Standard")
(check-expect (cheapest-format 10 7 1 50) "Kompakt")
(check-expect (cheapest-format 23.5 12.5 1 50) "Kompakt")
(check-expect (cheapest-format 14 9 0.5 50) "Kompakt")
(check-expect (cheapest-format 10 7 2 500) "Gross")
(check-expect (cheapest-format 35.3 25 2 500) "Gross")
(check-expect (cheapest-format 10 23.5 1 500) "Gross")
(check-expect (cheapest-format 10 7 5 1000) "Maxi")
(check-expect (cheapest-format 35.3 25 5 1000) "Maxi")
(check-expect (cheapest-format 10 7 2 1000) "Maxi")
(check-expect (cheapest-format 10 7 5 10) "Maxi")
(check-expect (cheapest-format 35.3 7 1 50) "Gross")
(check-expect (cheapest-format 14 25 0.5 20) "Gross")
(check-expect (cheapest-format 50 9 0.5 20) #false)
(check-expect (cheapest-format 10 50 1 50) #false)
(check-expect (cheapest-format 10 9 500 20) #false)
(check-expect (cheapest-format 10 9 1 9001) #false)
(check-expect (cheapest-format 0 0 0 0) #false)
(check-expect (cheapest-format 0 9 2 20) #false)
(check-expect (cheapest-format 10 0 0.5 50) #false)
(check-expect (cheapest-format 10 9 0 20) #false)
(check-expect (cheapest-format 10 9 0.5 0) #false)
(define (cheapest-format length width height weight)
(cond
[(format-possible? "Standard" length width height weight)
"Standard"]
[(format-possible? "Kompakt" length width height weight)
"Kompakt"]
[(format-possible? "Gross" length width height weight)
"Gross"]
[(format-possible? "Maxi" length width height weight)
"Maxi"]
[else
#false]))
;TASK-3
; Format Length Width Height Weight -> Boolean
; check whether we can send something as a given format
(define (format-possible? format length width height weight)
(and (in-range? length (min-length format) (max-length format))
(in-range? width (min-width format) (max-width format))
(below-maximum? height (max-height format))
(below-maximum? weight (max-weight format))
(above-minimum? (aspect-ratio length width)
(min-aspect-ratio format))))
; Maximum is a Number.
; interp. the upper bound of something
; Minimum is a Number.
; interp. the lower bound of something
; in-range?
; Number Minimum Maximum -> Boolean
; Check whether a number is between a minimum and a maximum
(check-expect (in-range? 5 0 10) #true)
(check-expect (in-range? 50 8 42) #false)
(define (in-range? number Minimum Maximum)
(cond
[(>= number Minimum) #true]
[(<= number Maximum) #true]
[else #false]))
; above-minimum?
; Number MaybeMinimum -> Boolean
; Check whether a number is above an optional minimum
(check-expect (above-minimum? 42 13) #true)
(check-expect (above-minimum? 35 99) #false)
(define (above-minimum? number sMaybeMinimum)
(cond
[(> number sMaybeMinimum) #true]
[(<= number sMaybeMinimum) #false]))
; below-maximum?
; Number Maximum -> Boolean
; Check whether a number is below a maximum
(check-expect (below-maximum? 10 15) #true)
(check-expect (below-maximum? 42 10) #false)
(define (below-maximum? number Maximum)
(cond
[(< number Maximum)#true]
[(>= number Maximum)#false]))
; min-length
; Format -> Minimum
; return minimum length of a format
(check-expect (min-length "Standard") 14)
(check-expect (min-length "Maxi") 10)
(check-expect (min-length "Kompakt") 10)
(check-expect (min-length "Gross") 10)
(define (min-length Format)
(cond
[(string=? "Standard" Format) 14]
[(string=? "Kompakt" Format) 10]
[(string=? "Gross" Format) 10]
[(string=? "Maxi" Format) 10]))
; max-length
; Format -> Maximum
; return maximum length of a format
(check-expect (max-length "Standard") 23.5)
(check-expect (max-length "Maxi") 35.3)
(check-expect (max-length "Kompakt") 23.5)
(check-expect (max-length "Gross") 35.3)
(define (max-length Format)
(cond
[(string=? "Standard" Format) 23.5]
[(string=? "Kompakt" Format) 23.5]
[(string=? "Gross" Format) 35.3]
[(string=? "Maxi" Format) 35.3]))
; min-width
; Format -> Minimum
; return minimum width of a format
(check-expect (min-width "Standard") 9)
(check-expect (min-width "Maxi") 7)
(check-expect (min-width "Kompakt") 7)
(check-expect (min-width "Gross") 7)
(define (min-width Format)
(cond
[(string=? "Standard" Format) 9]
[(string=? "Kompakt" Format) 7]
[(string=? "Gross" Format) 7]
[(string=? "Maxi" Format) 7]))
; max-width
; Format -> Maximum
; return maximum width of a format
(check-expect (min-width "Standard") 12.5)
(check-expect (min-width "Maxi") 25)
(check-expect (min-width "Kompakt") 12.5)
(check-expect (min-width "Gross") 25)
(define (max-width Format)
(cond
[(string=? "Standard" Format) 12.5]
[(string=? "Kompakt" Format) 12.5]
[(string=? "Gross" Format) 25]
[(string=? "Maxi" Format) 25]))
; max-height
; Format -> Maximum
; return maximum height of a format
(check-expect (max-height "Standard") 0.5)
(check-expect (max-height "Maxi") 5)
(check-expect (max-height "Kompakt") 1)
(check-expect (max-height "Gross") 2)
(define (max-height Format)
(cond
[(string=? "Standard" Format) 0.5]
[(string=? "Kompakt" Format) 1]
[(string=? "Gross" Format) 2]
[(string=? "Maxi" Format) 5]))
; max-weight
; Format -> Maximum
; return maximum weight of a format
(check-expect (max-weight "Standard") 20)
(check-expect (max-weight "Maxi") 1000)
(check-expect (max-weight "Kompakt") 50)
(check-expect (max-weight "Gross") 500)
(define (max-weight Format)
(cond
[(string=? "Standard" Format) 20]
[(string=? "Kompakt" Format) 50]
[(string=? "Gross" Format) 500]
[(string=? "Maxi" Format) 1000]))
; AspectRatio is a Number.
; interp. ratio of length to width
; aspect-ratio
; Length Width -> AspectRatio
; compute aspect ratio of letter
(check-expect (aspect-ratio 50 10) 5)
(check-expect (aspect-ratio 23.5 12.5) 1.88)
(check-expect (aspect-ratio 35 7) 5)
(define (aspect-ratio Length Width)
(/ Length Width))
; min-aspect-ratio
; Format -> MaybeMinimum
; return optional minimum aspect ratio of format
(check-expect (min-aspect-ratio "Standard") 1.4)
(check-expect (min-aspect-ratio "Kompakt") 1.4)
(check-expect (min-aspect-ratio "Gross") #false)
(check-expect (min-aspect-ratio "Maxi") #false)
(define (min-aspect-ratio Format)
(cond
[(string=? "Standard" Format) 1.4]
[(string=? "Kompakt" Format) 1.4]
[(string=? "Gross" Format)#false]
[(string=? "Maxi" Format)#false]))
; MaybeMinimum is one of:
; - #false
; - Minimum`
; interp. the lower bound of something, or #false if there's no lower bound
(define (maybe-minimum-template maybe-minimum)
(if (false? maybe-minimum)
...
(... maybe-minimum ...)))
当我运行此代码时，它给出了以下错误： “＆gt;：预期真实的第二个参数，给定#false”
我不明白为什么。当我隔离应该产生错误的函数时，它可以完美地工作。你有什么想法吗？
答案 0 :(得分：1)
min-aspect-ratio返回＆＃34; Gross＆＃34;的布尔值和＆＃34; Maxi＆＃34;。因此，在format-possible?中，测试(above-minimum? (aspect-ratio length width) (min-aspect-ratio format))失败。
我不熟悉BSL，但这些改变应该有所帮助：
(define (aspect-ratio Length Width)
(if (zero? Width) ; <=====
#false ; <=====
(/ Length Width)))
(define (above-minimum? number sMaybeMinimum)
(cond
[(boolean? number) number] ; <=====
[(boolean? sMaybeMinimum) sMaybeMinimum] ; <=====
[(> number sMaybeMinimum) #true]
[(<= number sMaybeMinimum) #false]))
没有更多错误，但60次测试中有20次失败。