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POContinuations and for comprehensions -- what's the incompatibility?
 

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  1. POContinuations and for comprehensions -- what's the incompatibility?
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    <p>I am new to Scala and trying to wrap my head around continuations I'm trying to reproduce the <code>yield return</code> C# statement.</p> <p>Following <a href="https://stackoverflow.com/a/2655394/116301">this post</a>, I have written the following code :</p> <pre><code>package com.company.scalatest import scala.util.continuations._; object GenTest { val gen = new Generator[Int] { def produce = { yieldValue(1) yieldValue(2) yieldValue(3) yieldValue(42) } } // Does not compile :( // val gen2 = new Generator[Int] { // def produce = { // var ints = List(1, 2, 3, 42); // // ints.foreach((theInt) =&gt; yieldValue(theInt)); // } // } // But this works? val gen3 = new Generator[Int] { def produce = { var ints = List(1, 2, 3, 42); var i = 0; while (i &lt; ints.length) { yieldValue(ints(i)); i = i + 1; } } } def main(args: Array[String]): Unit = { gen.foreach(println); // gen2.foreach(println); gen3.foreach(println); } } abstract class Generator[E] { var loopFn: (E =&gt; Unit) = null def produce(): Unit @cps[Unit] def foreach(f: =&gt; (E =&gt; Unit)): Unit = { loopFn = f reset[Unit, Unit](produce) } def yieldValue(value: E) = shift { genK: (Unit =&gt; Unit) =&gt; loopFn(value) genK(()) () } } </code></pre> <p>As you can see, <code>gen2</code> is commented out as it does not compile. Since I can easily iterate over the content of a list using a while loop (see <code>gen3</code>), I expected the foreach loop to work just as well.</p> <p>The compilation error is the following :</p> <pre><code>no type parameters for method foreach: (f: Int =&gt; B)Unit exist so that it can be applied to arguments (Int =&gt; Unit @scala.util.continuations.cpsParam[Unit,Unit]) --- because --- argument expression's type is not compatible with formal parameter type; found : Int =&gt; Unit @scala.util.continuations.cpsParam[Unit,Unit] required: Int =&gt; ?B </code></pre> <p><strong>Why do I get this error and is there a way to work around this with something cleaner than a while loop?</strong></p> <p>Thank you</p>
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    1. COpossible duplicate of [Implementing yield (yield return) using Scala continuations](http://stackoverflow.com/questions/2201882/implementing-yield-yield-return-using-scala-continuations)
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    2. COI'm not looking for a answer telling me how to reproduce 'yield return' using Scala continuations. I'm looking for the reason why the 'gen2' in my example doesn't work. The 'yield return' is just the context within which I encountered this issue.
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    3. COAh, sorry then.
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