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copied!<p>Flaviu's answer inspired me to try playing with implicits. The idea is to see if the trace looks better with the 'trace' further to the right on the line:</p> <pre><code>import Trace._ object Main { def main(args:Array[String]) { val listList = List(List(1,2,3), List(3,4)) for { list <- trace1(listList, "lList is: %s", listList) // trace() item <- list traced("list is: %s", list) // implicit } yield item </code></pre> <p>I also wanted to try mixing in error logging in the same comprehension. Error logging seems to look best mixed with Daniel's approach: </p> <pre><code> val optOpt:Option[Option[Int]] = Some(Some(1)) for { opt <- optOpt; _ = trace2("opt found: %s", opt) // trying Daniel's suggestion int <- opt orElse err("num not found in: %s", opt) // together with error logging } yield int } } </code></pre> <p>Here's the supporting code for both experiments:</p> <pre><code>object Trace { def trace1[T](any:T, message:String, params:AnyRef*):T = { Console println String.format("TRA: " + message, params:_*) any } def trace2[T](message:String, params:AnyRef*) { Console println String.format("TRA: " + message, params:_*) } def err[T](message:String, params:AnyRef*):Option[T] = { Console println String.format("ERR: " + message, params:_*) None } implicit def anyRefToTraceable[T](anyRef:T):Traceable[T] = { new Traceable(anyRef) } class Traceable[T](val self:T) { def traced(message:String, params:AnyRef*):T = { Console println String.format("TRA: " + message, params:_*) self } } } </code></pre>

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