Scala polling loop without vars - scala

Question

What's the Scala best-practice for polling and API?
I'm trying to write a Scala method that polls an API, checking if it reached "SUCCESS". While polling, it also might reach bad stated like "FAILED" or "TIMEOUT".
In Java, I'd write something like:
public String pollEndpoint() {
boolean isPolling = true;
String result = "NA";
while (isPolling) {
Response response = getResponse("http://myAPI.com/ready?id=1234");
if (response.status == "FAILED") { throw new FailedException(response.reason);}
else ... //Some other bad conditions
else if (response.status == "SUCCESS") {
isPolling = false;
result = response.result;
}
System.out.println("Current state is " + response.status); // When running, will be "RUNNING"
Thread.sleep(1000);
}
}
In Scala I can do:
def pollEndpoint():String = {
var isPolling = true
var result = "NA"
while (isPolling) {
val response = getResponse("http://myAPI.com/ready?id=1234")
if (response.status == "FAILED") { throw new FailedException(response.reason)}
else ... //Some other bad conditions
else if (response.status == "SUCCESS") {
isPolling = false
result = response.result
}
println("Current state is " + response.status); // When running, will be "RUNNING"
Thread.sleep(1000)
}
}
But this solution uses vars.
Is there any nice way of doing this, using only vals?

Answer 1

As Luis mentioned in comment, you can just write a recursive for that:
def pollEndpoint():String = {
val response = getResponse("http://myAPI.com/ready?id=1234")
println("Current state is " + response.status); // When running, will be "RUNNING"
if (response.status == "FAILED") { ??? }
else if (response.status == "SUCCESS") {
response.result
} else {
Thread.sleep(1000)
pollEndpoint()
}
}
The following will mock getResponse:
var i = 5
def getResponse(str: String): Response = {
if (i < 0) {
Response("SUCCESS", "Great success")
} else {
i = i - 1
Response("Wait", "Not done yet.")
}
}
And the call:
pollEndpoint()
Will produce:
Current state is Wait
Current state is Wait
Current state is Wait
Current state is Wait
Current state is Wait
Current state is Wait
Current state is SUCCESS
Having said all of that, it is way better instead of defining getResponse as it is, we might do:
def getResponse(str: String): Future[Response]
And then simply:
getResponse("http://myAPI.com/ready?id=1234").map { response =>
// Handle response
}

Answer 2

It depends on what information determines the repetition (i.e. when to loop) and what information is returned to the outside world, but under the right circumstances you might iterate() instead of looping or recursing.
def pollEndpoint():String = {
Iterator.iterate(getResponse("<yadda-yadda>")){ response =>
response.status match {
case "FAILED" => //log error, throw exception, etc.
case stat => //log whatever
Thread.sleep(1000)
}
getResponse("<yadda-yadda>")
}.dropWhile(_.status != "SUCCESS") //test for exit condition/s
.next().result
}