[Haskell-cafe] The promising world of Monadic formlets

Alberto G. Corona agocorona at gmail.com
Thu Jun 20 12:56:19 CEST 2013

Here is the example with better rendering and additional information as
well as some identifies issues to be solved.


And  I made strong statements there.

What do you think? If you have questions or want to be involved in
the development of this and other related concepts, please send me a

2013/6/20 Alberto G. Corona <agocorona at gmail.com>

> I don´t know how, but the google mail has changed the applicative functor
> operator after (,) Left and Rigth by  "<-".
> 2013/6/19 Alberto G. Corona <agocorona at gmail.com>
> Hi,
>> This is just to let you know the promising results of some
>> experimentation:
>> Formlets are about applicative instances, but what about monadic
>> instances? What a Monad instance of formlets means? I recently experimented
>> with this and the results are very interesting and powerful- It mixes the
>> best of web forms, with the flexibility of console applications. ???!!!!!!
>> Althoug this example is for the formlets of the MFlow
>> <https://github.com/agocorona/MFlow>framework , it can be ported to
>> other formlet implementations. Although the MFLow formlets include web
>> formatting that is not supported in other formlets implementations. Static
>> HTML templating don´t work well with monadic formlets, so it is important
>> to include the formatting as a  part of the computation:
>> import MFlow.Wai.Blaze.Html.All
>> dynamicForm= wform $ do
>>       (n,s) <- (,) <- p << "Who are you?"
>>                    ++> getString Nothing  <! hint "name"     <++ br
>>                    <*> getString Nothing  <! hint "surname"  <++ br
>>                    <** submitButton "ok" <++ br
>>       flag <- b << "do you " ++> getRadio[radiob "work?",radiob "study?"]
>> <++ br
>>       r<-case flag of
>>          "work" -> pageFlow "l"
>>                      $ Left  <- b << "do you enjoy your work? "
>>                                 ++> getBool True "yes" "no"
>>                                 <** submitButton "ok"  <++ br
>>          "study"-> pageFlow "r"
>>                      $ Right <- b << "do you study in "
>>                                   ++> getRadio[radiob "University"
>>                                          ,radiob "High School"]
>>       p << ("You are "++n++" "++s) ++>
>>        case r of
>>          Left fl ->   p << ("You work and it is " ++ show fl ++ " that
>> you enjoy your work")
>>                         ++> noWidget
>>          Right stu -> p << ("You study at the " ++ stu)
>>                         ++> noWidget
>> hint s= [("placeholder",s)]
>> onClickSubmit= [("onclick","this.form.submit()")]
>> radiob s n= text s ++> setRadio s n <! onClickSubmit
>> Here wform, getBool, getString , getRadio etc are formlet elements
>> The first sentence is an applicative composition that generate a 2 tuple,
>> to show that applicative and monadic can be mixed.  the operations ++> add
>> html to the formlet. the operatior <! add attributes to the formlet
>> element.. noWidget is a dumb formlet that does not validate.
>> The second monadic statement is an election between two options. The
>> beauty of the monadic instance is that the rest of the form can vary
>> depending on the previous answers.  Since the formlets validate the input,
>> unless the election is made, the radio will not validate, so the monadic
>> execution will be aborted beyond any unanswered question, so nothing will
>> appear after the question. The rest of the form will appear when the user
>> choose one of the two options. once one or the other option is chosen, then
>> another binary question is presented. (either he likes his work or where he
>> study).  When the questions are finised, the results are presented.
>> I hope that you get the idea. The benefit is not only the familiar coding
>> and presentation of a sequential console application: Since the form
>> encloses all the fields, At any time the user can change previous inputs
>> and the form will reflect these changes. For example if the user change
>> from work to study (second statements) the "where do you study will appear
>> and the work related questions and answers will disappear. That is
>> wonderfully useful for heavily interactive applications.
>> There is  a problem however and it is the issue of the formlet
>> identifiers. Unlike in an applicative presentation, now the number and type
>> of the formlets will vary, so the response to a previous form create a new
>> kind of form, and the post response can be misinterpreted. To avoid that ,
>> the  pageFlow call creates fixed field labels for each branch of execution.
>> I will release a version of MFlow that support this kind of monadic
>> composition of fomlets, but In essence it is nothing but to add Monad
>> instance to formlets. A single server procedure, that executes the formlet
>> code can support all the interaction so any framework can do it. The
>> usability of that is huge:It is possible to interact in a web page in a
>> console style with questions and answers with the versatitly of a dynamic
>> foms: Any modification in the form change the subsequent flow of
>> interaction. Another application of this monadic style is to ease multistep
>> processes such are registration, check-out and payment ad so on. Even a
>> entire interactive dynamic application can be coded in a single page.
>> And no javascript is needed!.
>> To run this formlet in MFlow:
>> main=do
>>   addMessageFlows
>>        [(""    , transient $ runFlow  $ ask dynamicForm )]
>>    wait $ run port waiMessageFlow
>> This video show how the presentation of this example vary with the user
>> input:
>> http://youtu.be/DryBQc9agFg
>> I hope that you find the idea interesting.  If you want to experiment
>> with this in MFlow, I have to say that the implementation of this feature
>> is in an early stage. The code is in the head branch
>> https://github.com/agocorona/MFlow/tree/head
>> Alberto.
> --
> Alberto.

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/haskell-cafe/attachments/20130620/a3128f00/attachment.htm>

More information about the Haskell-Cafe mailing list