32 lines
1.3 KiB
JavaScript
32 lines
1.3 KiB
JavaScript
// The single impure place in the course (with browser.js and main.js): everything else only builds values.
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// Here we interpret IO descriptions against a Platform and hold the one mutable variable, the current stream.
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// Platform = { fillRect, fillText, randomSeed, startClock, onKeyDown, onKeyUp }
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// Perform one op on the platform and return its result.
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const perform = (op, platform) => {
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if (op.tag === 'RandomSeed') return platform.randomSeed()
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const s = op.shape
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return s.tag === 'Rect'
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? platform.fillRect(s.x, s.y, s.w, s.h, s.color)
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: platform.fillText(s.x, s.y, s.text, s.color, s.size, s.align)
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}
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// A loop, not recursion: a scene is hundreds of ops and the stack must not grow with them.
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export const runIO = (io, platform) => {
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let current = io
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while (current.tag === 'Effect') current = current.k(perform(current.op, platform))
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return current.value
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}
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export const runApp = (main, platform) => {
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let stream = runIO(main, platform)
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const feed = (input) => {
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const [ios, next] = stream.step(input)
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stream = next
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ios.forEach((io) => runIO(io, platform))
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}
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platform.onKeyDown((key) => feed({ tag: 'KeyDown', key }))
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platform.onKeyUp((key) => feed({ tag: 'KeyUp', key }))
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platform.startClock((t) => feed({ tag: 'Time', t }))
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}
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