42 lines
1.3 KiB
Scheme
42 lines
1.3 KiB
Scheme
;; The first three lines of this file were inserted by DrScheme. They record metadata
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;; about the language level of this file in a form that our tools can easily process.
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#reader(lib "htdp-intermediate-lambda-reader.ss" "lang")((modname world) (read-case-sensitive #t) (teachpacks ((lib "universe.ss" "teachpack" "2htdp") (lib "foo.ss" "installed-teachpacks"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "universe.ss" "teachpack" "2htdp") (lib "foo.ss" "installed-teachpacks")))))
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;; testing world
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;; World = Nat
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(define world0 100)
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(define (world->image w)
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(place-image (circle 3 'solid 'red) 50 w (empty-scene 100 100)))
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(define (world->next w) (sub1 w))
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(define (world->steer w ke)
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(cond
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[(char? ke) w]
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[(symbol=? ke 'left) 100]
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[(symbol=? ke 'right) 90]
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[else w]))
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;; ---
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(check-expect (key-event? 'a) true)
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(check-expect (key-event? 0) false)
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(check-expect (key-event? #\a) true)
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(check-expect (key=? 'a 'b) false)
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(check-expect (key=? 'a #\a) false)
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(check-expect (key=? 'left 'left) true)
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(check-error (key=? 'a 0) "key=?: expected <KeyEvent> as second argument, given: 0")
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;; run world run
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xxx
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(big-bang world0
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(on-draw world->image)
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(on-tick world->next)
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(on-key world->steer)
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(stop-when zero?))
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