[英]Scheme struct with another struct
我試圖自己學習計划(運貨),但遇到了問題。
我正在嘗試使用不同的形狀,例如圓形,正方形和矩形。 任務如下:
“定義類型“圓形”,“正方形”和“矩形”並定義主要類型“形狀”。我需要在任務的下一部分中使用形狀結構,其中我必須定義一個函數“形狀區域” ”將獲得“形狀”數據束,並應表示任何給定形狀的區域。
這是我到目前為止的內容:
(define-struct square (nw lenght))
(define-struct circle (center radius))
(define-struct rectangle (nw width height))
(define-struct shape (...))
(define (area-of-shape shapeA)
(cond
[(square? (shapeA)) (* (square-lenght shapeA) (square-lenght shapeA))]
[(circle? (shapeA)) (* 3.14 (* (circle-radius shapeA) (circle-radius shapeA)))]
[(rectangle? (shapeA)) (* (rectangle-width shapeA) (rectangle-height shapeA))]))
如何定義結構shape
? 我嘗試了類似的東西
(define-struct shape (circle square rectangle))
但這沒有任何意義,因為該結構將需要所有3種形狀。
任何幫助,將不勝感激。
球拍結構可以從另一個結構繼承。 所以:
#lang racket
(struct shape ())
(struct square shape (nw length))
(struct circle shape (center radius))
(struct rectangle shape (nw width height))
(define (area-of-shape shape)
(if (shape? shape)
(cond
[(square? shape) (* (square-length shape) (square-length shape))]
[(circle? shape) (* 3.14 (* (circle-radius shape) (circle-radius shape)))]
[(rectangle? shape) (* (rectangle-width shape) (rectangle-height shape))]
[else (error 'area-of-shape "Unhandled Shape Condition.")])
(error 'area-of-shape "Argument not a Shape.")))
;; Example uses
(area-of-shape (square 0 10))
(area-of-shape (circle 0 10))
(area-of-shape (rectangle 0 10 10))
順便說一句,對於像area-of-shape
這樣的東西,我發現使用match
比cond
更方便:
(define (area-of-shape shape)
(match shape
[(square _ len) (* len len)]
[(circle _ rad) (* 3.14 (* rad rad))]
[(rectangle _ w h) (* w h)]))
我將按以下方式進行操作:
(define (area-of-shape shapeA)
(cond
[(square? shapeA) (* (square-lenght shapeA) (square-lenght shapeA))]
[(circle? shapeA) (* 3.14 (* (circle-radius shapeA) (circle-radius shapeA)))]
[(rectangle? shapeA) (* (rectangle-width shapeA) (rectangle-height shapeA))]
[else (error 'area-of-shape "A shape is either a square, a circle, or, a rectangle")]))
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