Statefulness means that the flow of execution is right in front of the eyes of the programmer, rather that in the spaghetti code of the event-handling model, the goto of the XXI century. it also means that the entire session is in a procedure, so the session data need no trickery.
Event sourcing in combination with statefulness means automatic logging of all the events and automatic recovery of the execution state of the server procedure and its data, thanks to the
Workflow monad transformer [2].
So the server procedure can be stopped after timeout and restarted by the application server when the user invokes it. The programmer can determine the timeout and for how long the state is stored.
Back button management: the
flow of execution can run back when the back button is pressed [3]. Thanks to a monad transformer. In combination with event sourcing, this means automatic rollback of user session data. So if the user want to undo his last item in the shopping cart, he only has to press the back button.
User interface:
It is made of self contained pieces called widgets, made around the formlet concept, so they compose gracefully with applicative operators and other extra operators. A MFlow widget is more like the widgets of XWindows,
ASP.NET or JavaServer Faces: they have their own HTML formatting, their own behaviours and interact with the server via AJAX, they execute actions when activated and they return statically typed data. They declare their required scripts, CSS links and server procedures in the form of requirements to the requirement service. They include the server and client code in the same piece of text. Being self contained and typed, they can be shared and plugged with a minimum of configuration and instructions.
The URL links are also widgets or elements of widgets and return data to the same flow, so no spaguetty event handling occur, unless the programmer need out-of-flow links.
This versions
includes some active widgets with server-side controls for creating them [4].
Bindings:
wai-warp, blaze-html, xhtml, HSP, hack.
Persistence and transactions:
Global data can be transacted with any kind of persistence framework. MFlow internally uses TCache [5], which provides with persistent STM references (DBRefs). Their serialization can be configured. For rapid prototyping, they have default persistence in files. Just add a Read-Show or a Binary instance for your data and you can have a persistent, transactional DBRef to it. Use them like you use TVars. TCache can index text and register fields. It has a simple query language. Data can be accessed by key or by any indexed field.
EXAMPLE:
The human mind learn by examples.
There is a online demo for some of the features that you can play with and you can download the code [6]