endpoint Diagram::Operation::Create do |ctx, **| redirect_to diagram_path(ctx[:diagram].id) end.Or do |ctx, **| render :form end

The flow pipetree is a mix of the Either monad and “Railway-oriented programming”, but not entirely the same.

It is based on the idea that each validation is encapsulated by a simple, stateless predicate that receives some input and returns either true or false.

It will return the result as a Dry::Monads::Result object which can be either successful or failure.

Now you can easily spot them! The rule is: if you see a Result it means that this function can throw an exception. And you even know its type in advance.

bind applies unwrapped Success value to the block, which should return a Result object. No-op on Failure

In this article, we’ll take a look at using the ‘Either monad’ as an alternative to try...catch.