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    <p>(Edited to give a correct answer!)</p> <p>The key here is that <code>Future</code> and <code>Option</code> <em>don't compose inside <code>for</code></em> because there aren't the correct <code>flatMap</code> signatures. As a reminder, for desugars like so:</p> <pre><code>for ( x0 &lt;- c0; w1 = d1; x1 &lt;- c1 if p1; ... ; xN &lt;- cN) yield f c0.flatMap{ x0 =&gt; val w1 = d1 c1.filter(x1 =&gt; p1).flatMap{ x1 =&gt; ... cN.map(xN =&gt; f) ... } } </code></pre> <p>(where any <code>if</code> statement throws a <code>filter</code> into the chain--I've given just one example--and the equals statements just set variables before the next part of the chain). Since you can only <code>flatMap</code> other <code>Future</code>s, every statement <code>c0</code>, <code>c1</code>, ... except the last had better produce a <code>Future</code>.</p> <p>Now, <code>getUserDetails</code> and <code>getSchool</code> both produce <code>Futures</code>, but <code>sid</code> is an <code>Option</code>, so we can't put it on the right-hand side of a <code>&lt;-</code>. Unfortunately, there's no clean out-of-the-box way to do this. If <code>o</code> is an option, we can</p> <pre><code>o.map(Future.successful).getOrElse(Future.failed(new Exception)) </code></pre> <p>to turn an <code>Option</code> into an already-completed <code>Future</code>. So</p> <pre><code>for { ud &lt;- userStore.getUserDetails(user.userId) // RHS is a Future[Either[...]] sid = ud.right.toOption.flatMap(_.schoolId) // RHS is an Option[Int] fid &lt;- sid.map(Future.successful).getOrElse(Future.failed(new Exception)) // RHS is Future[Int] s &lt;- schoolStore.getSchool(fid) } yield s </code></pre> <p>will do the trick. Is that better than what you've got? Doubtful. But if you</p> <pre><code>implicit class OptionIsFuture[A](val option: Option[A]) extends AnyVal { def future = option.map(Future.successful).getOrElse(Future.failed(new Exception)) } </code></pre> <p>then suddenly the for-comprehension looks reasonable again:</p> <pre><code>for { ud &lt;- userStore.getUserDetails(user.userId) sid &lt;- ud.right.toOption.flatMap(_.schoolId).future s &lt;- schoolStore.getSchool(sid) } yield s </code></pre> <p>Is this the best way to write this code? Probably not; it relies upon converting a <code>None</code> into an exception simply because you don't know what else to do at that point. This is hard to work around because of the design decisions of <code>Future</code>; I'd suggest that your original code (which invokes a filter) is at least as good of a way to do it.</p>
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    1. COThis is giving me a compile error. found : scala.concurrent.Future[Option[com.authorpub.userservice.School]] required: Option[?] s <- schoolStore.getSchool(sid)
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    2. COCan you explain what all your types are? It's a little hard to tell given that you haven't posted full working code. What is a future and what is an option in your working code? You can get Scala 2.10 to print out the type of an expression if you do this: `import scala.reflect.runtime.universe._; def typeme[A: TypeTag](a: A) = { println(implicitly[TypeTag[A]]); a }` and then wrap the expression in `typeme`, e.g. `sid = typeme(ud.right.toOption.flatMap(_.schoolID))`.
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    3. COSomeone downvoted without comment. This isn't very useful. What's wrong with the answer as it stands now?
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