27 lines
1.1 KiB
TypeScript
27 lines
1.1 KiB
TypeScript
import {ImpType} from '../core/Dispatcher.js'
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export const number_type = {
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before: ['Complex'],
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test: (n: unknown): n is number => typeof n === 'number',
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from: {string: s => +s}
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}
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export interface NumbersReturn<Params> {
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// The following description of the return type of `zero` on a single
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// number argument has ended up unfortunately rather complicated. However,
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// it illustrates the typing is really working: Suppose we have a
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// `type Small = 1 | 2 | 3`. Then Small indeed extends number, but we
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// can't use the operation `zero(s: Small)` because zero is supposed to
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// return something of the same type as its argument, but there is no
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// zero in Small. Anyhow, in plain language the below says that given
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// one parameter of a subtype of number, as long as that subtype includes 0,
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// the zero operation returns a member of the type `0` (so we know even
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// at compile time that its value will be 0).
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zero: Params extends [infer T]
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? T extends number ? 0 extends T ? 0 : never : never
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: never
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}
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export const zero: ImpType<'zero', [number]> = a => 0
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