Arrow-style Either Type

1import arrow.core.*
2import arrow.core.raise.*
3 
4sealed class UserError {
5    data class NotFound(val id: Int) : UserError()
6    data class ValidationError(val message: String) : UserError()
7    data object DatabaseError : UserError()
8}
9 
10data class User(val id: Int, val name: String, val email: String)
11 
12fun findUser(id: Int): Either<UserError, User> =
13    if (id > 0) {
14        User(id, "User$id", "user$id@example.com").right()
15    } else {
16        UserError.NotFound(id).left()
17    }
18 
19fun validateEmail(email: String): Either<UserError, String> =
20    if (email.contains("@")) email.right()
21    else UserError.ValidationError("Invalid email").left()
22 
23fun processUser(id: Int): Either<UserError, String> = either {
24    val user = findUser(id).bind()
25    val validEmail = validateEmail(user.email).bind()
26    "Processed: ${user.name} <$validEmail>"
27}
28 
29fun main() {
30    when (val result = processUser(1)) {
31        is Either.Left -> println("Error: ${result.value}")
32        is Either.Right -> println(result.value)
33    }
34}