Using fp-ts for Functional Programming in TypeScript/

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Solution Review: Working with Either and Pipe

Solution Review: Working with Either and Pipe

Let’s look at the solution to the coding challenge of "Working with Either and Pipe" in our application.

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Solution

Let’s see how we use the Either and pipe() functions in the below code.

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const checkValidHour = (hour: number): E.Either<string, number> => {
    return hour > 0 && hour <= 24 ? E.right(hour) : E.left('invalid hour');
};
const mapToGreeting = (hour: number) => {
    return hour < 12 ? 'good morning' : 'good afternoon';
};
const application = (hour: number) => {
    return pipe(
        checkValidHour(hour),
        h => E.map(mapToGreeting)(h),
        E.getOrElse(() => 'unknown greeting'),
    );
};
console.log(application(8));
console.log(application(13));
console.log(application(25));
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