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POSuccess/failure chain pattern in Scala
 

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    <p>I have a workflow like this:</p> <pre><code>parse template -&gt; check consistency -&gt; check conformance of one template to another parse template -&gt; check consistency </code></pre> <p>Either one of those steps may fail. I would like to implement that in Scala, preferably so that the parallel branches get evaluated independently merging both their errors. Perhaps in a monadic style but I am curious about some general OOP pattern too. Currently I have multiple variations hardcoded for various actions with the chaining like this</p> <pre><code>def loadLeftTemplateAndForth (leftPath : String, rightPath : String) = { val (template, errors) = loadTemplate(leftPath) if(errors.isEmpty) loadRightTemplateAndForth(template, rightPath) else popupMessage("Error.") } </code></pre> <p>which I bet must be some kind of antipattern. The steps need decoupling from the workflow but I was not able to come up with anything extremely elegant and there must proven ways already.</p> <p><strong>EDIT:</strong> Ok, so I have unsuccessfully tried to implement something like this</p> <pre><code>(((parseTemplate(path1) :: HNil).apply(checkConsistency _) :: ((parseTemplate(path2) :: HNil).apply(checkConsistency _)) :: HNil).apply(checkConformance _) def checkConformance (t1 : Template)(t2 : Template) : Seq[Error] </code></pre> <p>The functions would then return Success(result) or Failure(errors). I was using HLists but got lost in the type inference rules and other issues. It seems I was pretty close though. For someone knowledgable of this stuff it would probably be a piece of cake.</p> <p><strong>EDIT:</strong> I have finally managed to implement this</p> <pre><code>(parseTemplate("Suc") :: Args).apply(checkConsistency _) :: (parseTemplate("Suc") :: Args).apply(checkConsistency _) :: Args) .apply(checkConformance _) </code></pre> <p>with some unfornate constraints that each function must return my equivalent of Either and that the error type of applied function must be a subtype of arguments' error type. I did it using HList, application typeclass and a wrapper class Successful/UnsuccessfulArgList.</p>
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