jackson

Option

!effect { ioRecurseNTimes(n - 1) }.bind()

val deferredReply = async { startListening(replyChannel) }
sendChannel.send(message)
val reply = defferedReply.await()

@extension interface Bla<T> {
  fun showLogin(par: T): ReaderT<ForIO, Context, Unit> = ... // some ugly ReaderT blob
}

Good day. I'm new to functional programming and the arrow library and was wondering if anybody can help me.

I was wondering how one handles resources like database pools or connections and how you pass them to a function. For instance: Let say I have an authenticate method:

fun authenticate(username: String, password: String): Either<Error, Token> {

// validation etc ..

val user = getUserByUsername(username)

}

fun getUserByUsername(username: String): Option<User> {

// JDBC Query for user

val rs = con.prepareStatement("SELECT * FROM user .....")

....

val user = mapRowToUser(rs) // etc

return Option.fromNullable(user)

}

My question is do I pass in the connection of database pool as a parameter like so:

fun authenticate(con: Connection, username: String, password: String) ....

fun getUserByUsername(con: Connection, username: String): Option<User>  ...

What is the best practice when it comes to functional programming?

Also from what I have read and if my understanding is correct, this is impure and normally IO would be used?

fun getUserByUsername(username: String): IO<Option<User>>

Is this correct? Any help appreciated

IO

typealias Disposeable = () -> Unit

IO

fun <A> IOOf<A>.suspendCancellable() : Either<Throwable, A> =
 suspendCancellableCoroutine { continuation ->
    val disposable = fix().unsafeRunSyncCancellable {  continuation.resume(it) }
    continuation.invokeOnCancellation { disposable.invoke() }
  }

arrow-android

Either<Throwable, Unit>

.handleErrorWith { IO { log(it) }  }