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    <p>By defining those utility functions</p> <pre><code>implicit def eitherOps[E, A](v: Either[E, A]) = new { def map[B](f: A =&gt; B) = v match { case Left(e) =&gt; Left(e) case Right(a) =&gt; Right(f(a)) } def flatMap[B](f: A =&gt; Either[E, B]) = v match { case Left(e) =&gt; Left(e) case Right(a) =&gt; f(a) } def or(a: A) = v match { case Left(_) =&gt; Right(a) case x =&gt; x } } def secure[A, B](f: A =&gt; B) = new { def run(a: A): Either[Trowable, B] = try { Right(f(a)) } catch { case e =&gt; Left(e) } } </code></pre> <p>and simplifying yours</p> <pre><code>def fA(s : String) = 7 def fB(i : Int) = 1.0 def fC(d : Double) = true </code></pre> <p>We'll have:</p> <pre><code>def test(s: String): Either[Throwable, Double] = for { a &lt;- secure(fA).run(s).or(0) b &lt;- secure(fB).run(a).or(0.0) c &lt;- secure(fC).run(b).or(false) } yield result(a, b, c) </code></pre> <p><strong>Edit</strong></p> <p>Here's an executable but sadly, more verbose code snippet</p> <pre><code>object Example { trait EitherOps[E, A] { def self: Either[E, A] def map[B](f: A =&gt; B) = self match { case Left(e) =&gt; Left(e) case Right(a) =&gt; Right(f(a)) } def flatMap[B](f: A =&gt; Either[E, B]) = self match { case Left(e) =&gt; Left(e) case Right(a) =&gt; f(a) } def or(a: A) = self match { case Left(_) =&gt; Right(a) case x =&gt; x } } trait SecuredFunction[A, B] { def self: A =&gt; B def secured(a: A): Either[Throwable, B] = try { Right(self(a)) } catch { case e =&gt; Left(e) } } implicit def eitherOps[E, A](v: Either[E, A]) = new EitherOps[E, A] { def self = v } implicit def opsToEither[E, A](v: EitherOps[E, A]) = v.self implicit def secure[A, B](f: A =&gt; B) = new SecuredFunction[A, B]{ def self = f } def fA(s : String) = 7 def fB(i : Int) = 1.0 def fC(d : Double) = true def result(i : Int, d : Double, b : Boolean) = { if (b) d else i } def test(s: String): Either[Throwable, Double] = for { a &lt;- (fA _).secured(s) or 0 b &lt;- (fB _).secured(a) or 0.0 c &lt;- (fC _).secured(b) or false } yield result(a, b, c) } </code></pre>
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    1. POMore idiomatic (monadic?) way to express this Scala
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    1. USYo Eight
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    1. COAs I said in the question, the definitions provided for fA, fB & fC are just dummy defs, to allow the code to compile. Optimising them as you have done misses the point.
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    2. COThere is no optimization. You don't need to carry around other computed values since I provided default value if computation failed and they're in scope through the monadic computation. Unless you've already run the code, I think you missed the point of my post
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    3. COYo your post is good, (besides it doesn't compile OOTB) . We need to coomunicate the difference with this approach. The problem is indeed the sequential thinking, this is in my opinion the root of jons alidation problem. And that is what apparently got lost in all answers here. The point is jon you have to encode possible failure within the result type of your methods otherwise you won't get 'Monadic' benefits.
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