36 lines
1.0 KiB
Racket
36 lines
1.0 KiB
Racket
#lang typed-scheme
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(define-struct: rect ((nw : Symbol) (width : Number) (height : Number)))
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(define-struct: circ ((cntr : Symbol) (radius : Number)))
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(define-struct: over ((top : Shape) (bot : Shape)))
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(define-type-alias Shape (Rec Shape (U Plain over [Listof Plain])))
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(define-type-alias Plain (U rect circ))
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;; (define-type-alias Rect (U (make-rect Posn Number Number)))
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;; Circ = (make-circ Posn Number)
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(: area (Shape -> Number))
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;; the area of all rectangles in this s
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(define (area s)
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(cond
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[(plain? s) (plain-area s)]
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[(over? s) (+ (area (over-top s)) (area (over-bot s)))]
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[else (apply + (map rect-area (filter rect? s)))]))
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(: plain? (Any -> Boolean : Plain))
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;; is this p a plain shape?
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(define (plain? p)
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(or (rect? p) (circ? p)))
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(: plain-area (Plain -> Number))
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;; the area of this plain shape s
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(define (plain-area s)
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(cond
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[(rect? s) (rect-area s)]
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[(circ? s) 0]))
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(: rect-area (rect -> Number))
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;; the area of this rectangle r
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(define (rect-area s)
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(* (rect-width s) (rect-height s)))
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