RailwayOP-Basic.kt

sealed class Result<T>
data class Success<T>(val value: T): Result<T>()
data class Failure<T>(val errorMessage: String): Result<T>()

infix fun <T,U> Result<T>.compose(f: (T) -> Result<U>) = 
    when (this) {
        is Success -> f(this.value)
        is Failure -> Failure(this.errorMessage)
    }

fun main(args: Array<String>) {
    (input("Enter your name") compose ::notBlank compose ::lengthWithin10).let {
        when (it) {
            is Success -> println("Your name is: ${it.value}")
            is Failure -> println("Something went wrong: ${it.errorMessage}")
        }
    }
}

fun input(prompt: String): Result<String> {
    print("$prompt: ")
    val line = readLine()
    if (line == null) {
        return Failure("Unexpected end of input")
    }
    return Success(line)
}

fun notBlank(input: String): Result<String> = 
    if (input != "") Success(input) else Failure("Blank input")

fun lengthWithin10(input: String): Result<String> = 
    if (input.length <= 10) Success(input) else Failure("Input should be within 10 letters")