[Haskell-cafe] dynamic web form generation for algebraic data types

[Ivan Perez]

All of this reminds me of Conal Elliott's Tangible Values.

http://conal.net/papers/Eros/

(Not for web but the idea still applies.)

Ivan

On Thu, 2 Mar 2023 at 07:02, Olaf Klinke <olf at aatal-apotheke.de> wrote:

> On Thu, 2023-03-02 at 15:51 +0200, Georgi Lyubenov wrote:
> > Hey Olaf,
> >
> > This is not an answer to your question, but I was reminded of Grace[0],
> > which is a language
> > with a "browser"[1] that allows you to type in terms and get back
> > webpages based on those terms
> > "automagically", which sounds like exactly what you need. I don't know
> > how it's implemented, so I don't know if
> > it is actually relevant to you, but it is worth noting that Grace itself
> > is implemented in Haskell.
> >
> > Cheers,
> > Georgi
> >
> > [0] https://github.com/Gabriella439/grace
> > [1] https://trygrace.dev/
> >
> > On 3/2/23 12:54, Olaf Klinke wrote:
> > > Dear Cafe,
> > >
> > > has anyone ever attempted (and maybe succeeded) in building dynamic
> > > forms using one of the Haskell web frameworks (Yesod,Servant,...)?
> > > By "dynamic" form I mean a form that changes the number of fields based
> > > on selections the user makes in other fields of the form.
> > >
> > > For example, say one has an algebraic data type
> > >
> > >      data T = Number Int | Check Bool T
> > >
> > > A form for such a type would initially consist of radio buttons or a
> > > drop-down list with options "Number" and "Check" that lets the user
> > > select the constructor. When "Number" is selected, an <input
> > > type="number"> field is shown. When "Check" is selected, an <input
> > > type="checkbox"> is displayed next to another form of this kind.
> > >
> > > In the end, one would use the GHC.Generics machinery to generate forms
> > > for a wide range of algebraic data types. I've seen this in the Clean
> > > language's iTask library [1] and it's very convenient.
> > > Of course this would involve a lot of JavaScript like
> > > document.createElement() as well as book-keeping how to re-asseble the
> > > fields into a T value upon submission. At least the latter is already
> > > handled by libraries such as yesod-form.
> > >
> > > Olaf
> > >
> > > [1] https://cloogle.org/src/#itasks/iTasks/UI/Editor/Generic
> > > [2] https://github.com/haskell-servant/servant-swagger/issues/80
> > >
> > >
>
> Thanks for the pointer!
>
> The Grace README says under Notable Omissions:
>
> >Recursion or recursive data types
> >
> >Grace only supports two built-in recursive types, which are List and
> >JSON, but does not support user-defined recursion or anonymous
> >recursion.
> >
> >User-defined datatypes
> >
> >All data types in Grace are anonymous (e.g. anonymous records and
> >anonymous unions), and there is no concept of a data declaration
>
> The tutorial shows how Grace function inputs are mapped to forms, where
> functions with List input indeed have a form that is "dynamic" in the
> sense I defined. Otherwise there is only one input field per function
> argument. That means complex types are to be input in JSON syntax and
> parsed.
> Instead of a DSL, I'd prefer a shallow embedding into Haskell, so that
> one can leverage all the available machinery.
> Yet Grace already goes a long way towards what I am after.
>
> Olaf
>
>
>
>
>
>
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