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Implementation of Maybe (Optional) in TypeScript.
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| type None = void | null | undefined; | |
| const isNone = (value: unknown): value is None => { | |
| return value === null || typeof value === 'undefined'; | |
| }; | |
| const isMaybe = (value: unknown): value is Maybe<any> => { | |
| return !!(value && (value as { _isMaybe?: any })._isMaybe); | |
| }; | |
| type MaybePattern<T, U> = { | |
| none: () => U; | |
| some: (value: T) => U; | |
| }; | |
| type Maybe<T> = { | |
| _isMaybe: true, | |
| get: (placeholder: T) => T; | |
| map: <U>(fn: (value: T) => U) => Maybe<U>; | |
| match: <U>(pattern: MaybePattern<T, U>) => U; | |
| unwrap: () => T | None; | |
| }; | |
| const None = <T>(): Maybe<T> => ({ | |
| _isMaybe: true, | |
| get: (placeholder) => placeholder, | |
| map: () => None(), | |
| match: (pattern) => pattern.none(), | |
| unwrap: () => undefined, | |
| }); | |
| const Some = <T>(value: T): Maybe<T> => { | |
| if (isNone(value)) | |
| throw new Error('Value is not some.'); | |
| return { | |
| _isMaybe: true, | |
| get: () => value, | |
| map: (fn) => { | |
| const _value = fn(value); | |
| return isMaybe(_value) ? _value : Maybe(_value); | |
| }, | |
| match: (pattern) => pattern.some(value), | |
| unwrap: () => value, | |
| }; | |
| }; | |
| const Maybe = <T>(value: T | None): Maybe<T> => { | |
| return isNone(value) ? None<T>() : Some<T>(value); | |
| }; | |
| export { isNone, None, Some, isMaybe, Maybe, MaybePattern }; | |
| export default Maybe; |
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