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refactor: add utility to err on unreachable branches (#991)
and use it in pattern matching over all key/value map type pairs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,90 @@ | ||
| /* eslint-disable @typescript-eslint/no-explicit-any */ | ||
| type Extend<T extends any[], H> = H extends infer A ? [...T, A] : never; | ||
| type Flat<TS extends any[], R extends any[] = []> = TS extends [ | ||
| infer H, | ||
| ...infer T, | ||
| ] | ||
| ? Flat<T, Extend<R, H>> | ||
| : R; | ||
|
|
||
| declare const NoSuchCase: unique symbol; | ||
| interface NoSuchCaseBug<L> extends Array<never> { | ||
| [NoSuchCase]: L; | ||
| } | ||
| type On<I extends any[], O> = { | ||
| on: <const DI extends any[]>( | ||
| ...key: I extends Flat<DI> ? DI : NoSuchCaseBug<DI> | ||
| ) => <const DO>( | ||
| handler: (...args: Extract<I, Flat<DI>>) => DO, | ||
| ) => MV<Exclude<I, Flat<DI>>, O | DO>; | ||
| }; | ||
|
|
||
| declare const CasesAreNotExhaustive: unique symbol; | ||
| interface NonExhaustiveBug<L> { | ||
| [CasesAreNotExhaustive]: L; | ||
| } | ||
| type End<I extends any[], O> = [I] extends [never] | ||
| ? EndInternal<I, O> | ||
| : { | ||
| otherwise: <const DO>(handle: (...input: I) => DO) => O | DO; | ||
| end: NonExhaustiveBug<I>; | ||
| }; | ||
| type MV<I extends any[], O> = End<I, O> & On<I, O>; | ||
|
|
||
| type OnInternal<I extends any[], O> = { | ||
| on: <const DI extends any[]>( | ||
| ...key: DI | ||
| ) => <const DO>( | ||
| handler: (...args: Extract<I, Flat<DI>>) => DO, | ||
| ) => MVInternal<Exclude<I, Flat<DI>>, O | DO>; | ||
| }; | ||
| type EndInternal<I extends any[], O> = { | ||
| otherwise: <const DO>(handle: (...input: I) => DO) => O | DO; | ||
| end: () => O; | ||
| }; | ||
| type MVInternal<I extends any[], O> = EndInternal<I, O> & OnInternal<I, O>; | ||
|
|
||
| const deepMatch = (a: unknown, b: unknown): boolean => { | ||
| if ( | ||
| a === b && | ||
| ["number", "string", "boolean", "bigint"].includes(typeof a) && | ||
| typeof a === typeof b | ||
| ) { | ||
| return true; | ||
| } | ||
| if (a === null || b === null) { | ||
| return a === b; | ||
| } | ||
| if (typeof a === "object" && typeof b === "object") { | ||
| if (Array.isArray(a) && Array.isArray(b) && a.length === b.length) { | ||
| return a.every((a, i) => deepMatch(a, b[i])); | ||
| } else { | ||
| return Object.entries(b).every(([k, b]) => | ||
| deepMatch(k in a ? (a as any)[k] : undefined, b), | ||
| ); | ||
| } | ||
| } | ||
| return false; | ||
| }; | ||
|
|
||
| export const match = <const I extends any[]>( | ||
| ...args: I | ||
| ): MV<Flat<I>, never> => { | ||
| const rec = <I extends any[], O>(end: () => O): MVInternal<I, O> => ({ | ||
| end, | ||
| otherwise: (handler) => handler(...(args as unknown as I)), | ||
| on: | ||
| <const DI extends any[]>(...match: DI) => | ||
| <const DO>(handler: (...args: Extract<I, Flat<DI>>) => DO) => | ||
| rec<Exclude<I, Flat<DI>>, O | DO>(() => | ||
| deepMatch(args, match) | ||
| ? handler( | ||
| ...(args as unknown as Extract<I, Flat<DI, []>>), | ||
| ) | ||
| : end(), | ||
| ), | ||
| }); | ||
| return rec<Flat<I>, never>(() => { | ||
| throw new Error("Not exhaustive"); | ||
| }) as MV<Flat<I>, never>; | ||
| }; |