Either and fmap simple (and not formal) implementation

SimpleEitherScript.groovy

enum EitherStatus {
    LEFT, RIGHT
}

class Either {
    EitherStatus status = EitherStatus.RIGHT
    Map data

    String toString() {
        return "[${this.status}] > ${this.data}"
    }
}

Closure printName = { Either either ->
    if (either.data.firstName) {
        println "First Name: ${either.data.firstName}"
        return either
    } else {
        return [status: EitherStatus.LEFT, data: [error: 'First name not found']] as Either
    }
}

Closure printLastName = { Either either ->
    if (either.data.lastName) {
        println "Last Name: ${either.data.lastName}"
        return either
    } else {
        return ([status: EitherStatus.LEFT, data: [error: 'Last Name not found']] as Either)
    }
}

Closure printFullName = { Either either ->
    if (either.data.firstName && either.data.lastName) {
        println "Full Name: ${either.data.firstName} ${either.data.lastName}"
        return either
    } else {
        return ([status: EitherStatus.LEFT, data: [error: 'First or Last Name not found']] as Either)
    }
}

Either bind(Either either, Closure... methods) {
    for (Closure method : methods) {
        if (either.status == EitherStatus.LEFT) {
            break
        } else {
            either = method.call(either)
        }
    }
    return either
}

Either either = [status: EitherStatus.RIGHT, data: [firstName: 'John', lastName: 'Doe']] as Either
Either result
result = bind(either, printName, printLastName, printFullName)

println "RESULT: $result"

println '\n------------------------------------------------------'

either.data.lastName = ''
result = bind(either, printName, printLastName, printFullName)
println "RESULT: $result"