From briefly reading the wiki page https://wiki.haskell.org/Tangible_Value, it looks like it relies on Applicative functors for combining values. So maybe the missing piece for sum-types was Selective functors https://hackage.haskell.org/package/selective?

Gustavo Bicalho

---------- Forwarded message ---------- From: Olaf Klinke To: Ivan Perez Cc: "Haskell Café" Bcc: Date: Thu, 02 Mar 2023 17:40:18 +0100 Subject: Re: [Haskell-cafe] dynamic web form generation for algebraic data types On Thu, 2023-03-02 at 07:34 -0800, Ivan Perez wrote:

...

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

Yes, the concept has been re-invented multiple times, as is the case with most good ideas. TVs are general enough to bolt a web interface on top, I guess.

Seems that Conal, too, has not solved the sum type problem. The tangible value GADT https://hackage.haskell.org/package/TV-0.5.0/docs/Interface-TV-Input.html has a Pair constructor but not for Sum. I wonder whether there is a deeper categorical reason for this.

So I should re-phrase my question: Has anyone extended tangible values to Generic types and given them a modern html interface?

Olaf