Error handling example

Author: mateuszjancy

workshop07/FreeTransformer/src/main/scala/freetransformer/Interpreter.scala

@@ -1,9 +1,24 @@
 package freetransformer
 
+import freetransformer.Language.{Data, Error}
+
 import scala.util.{Failure, Success}
-import scalaz.Free
+import scalaz._
+
+trait ErrorPolicy {
+  def error(ex: Throwable): Free[Data, Nothing]
+}
 
-object Interpreter {
+trait GlobalErrorPolicy extends ErrorPolicy {
+  override def error(ex: Throwable): Free[Data, Nothing] = ex match {
+    case ex: Exception =>
+      val e: Free[Data, Nothing] = Free.liftF(Error(ex))
+      e
+  }
+}
+
+trait Interpreter {
+  this: ErrorPolicy =>
 
   import Language._
   import Logic._
@@ -12,11 +27,8 @@ object Interpreter {
     case Read(data, next) =>
       val d = core.read(data)
       d match {
-        case Success(value) =>
-          run(core, next(value))
-        case Failure(ex) =>
-          val e: Free[Data, Nothing] = Free.liftF(Error(ex))
-          run(core, e)
+        case Success(value) => run(core, next(value))
+        case Failure(ex) => run(core, error(ex))
       }
     case CalculateA(_, next) => run(core, next(core))
     case CalculateB(_, next) => run(core, next(core))
@@ -25,3 +37,5 @@ object Interpreter {
     case Error(ex) => Left(ex.getMessage)
   }, (a: A) => Right(a))
 }
+
+object Interpreter extends GlobalErrorPolicy