I also think it would be really good to have some documentation that explains the type system and how to do neat things with it in terms that a reasonably competent haskell / ML programmer could understand. I played around with Ur/Web about a year ago and was able to make a simple application, and use some C libraries (the C FFI is really easy to use), but realized that I wasn't able to do much of anything beyond mimicking the demos in various ways, mainly because the documentation was so sparse (when I didn't know how to do something, I just tried to do what I would expect it to do if it were haskell, which worked a surprising amount of the time, but wasn't the most enjoyable experience). Looking at, for example, page 19 of the reference manual [1], which is supposed to explain how expressions are typed (which I would assume would give input into how the type system worked), I, probably like Chris, couldn't make much sense of it. Now I don't have a PhD in type theory, or even a masters degree, but if your intended audience includes people like me, the documentation definitely needs work! Now perhaps understanding those tables isn't actually important to using the language, but from looking through the manual / available documentation, there seems to be the really basic cookbook style stuff, that you can copy and paste and modify, as long as you are careful, then the source code itself, from which more can be gleaned, and then this type of type theory. Because of this (or until there is real documentation explaining some of the novel things about this language), I think Ur/Web is going to remain a cool thing that barely anyone can do anything with. Something to be linked in reddit or stack overflow posts, but not actually used! It seems like documentation of the really basic stuff is there, and the really advanced stuff (which is great, don't get me wrong), but the stuff in the middle is missing! Which is too bad, because it seems like it is doing some really exciting things. 1. http://www.impredicative.com/ur/manual.pdf On Jul 13, 2011, at 11:10 AM, Christopher Done wrote:

On 13 July 2011 15:28, Adam Chlipala wrote:

...

I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects.

More information on Ur/Web can be found here: http://www.impredicative.com/ur/

I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers. I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok. I tried to get it running a while ago and could not get it to compile. I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database.

I like the idea, please keep us posted about it.

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Christopher Done wrote:

I also find it hard to understand the type system in a non-superficial level because the related paper was very hard to grok.

I'll only claim it's a fairly breezy read for people familiar with dependent type theory, which admittedly is not a huge crowd, even as a proportion of the Haskell community. More accessible documentation of that aspect is on my to-do list. I'm more or less waiting to start it until I get this current commercial project staffed properly. I know it _is_ possible to learn the interesting type system features well enough with just the existing documentation, because one programmer on the project, who has no CS research background, has managed to do it without much apparent trouble.

I tried to get it running a while ago and could not get it to compile.

You couldn't get the compiler to compile? No one has reported problems recently, so I suspect everything would Just Work today, if you're using Linux or OS X (and possibly in other cases).

I would also like to see how it handles non-web stuff as inevitably IME web applications involve more than merely reading and writing to a database.

I have no near-term plans to build an Ur implementation that handles non-web applications. There is an FFI, though. Yves_Pares wrote:

It'd also be interesting to know what you missed in Haskell web development so that you needed to build a new language inspired from it.

The key piece is precisely the basis of my paper "Ur: Statically-Typed Metaprogramming with Type-Level Record Computation." Haskell is missing the features that I think are critical for pleasant type-level computation, in particular of the variety that I use in the examples detailed in the paper. I'll leave the rest of my argument to be read out of the paper by those with enough background to do so. Folks without that background might at least read the case studies part of the paper and consider how such things might be implemented in Haskell, with equivalent or stronger static guarantees. Ertugrul Soeylemez wrote:

Christopher Done wrote:

...

...

...

...

I write to mention briefly that I'm looking for people interested in writing Ur/Web programs for pay. Ur/Web is a DSL for building modern web applications, and I believe it is truly a secret weapon for that domain, and one that should appeal to many Haskell fans. I have one customer now for whom I'm leading a project to develop a particular web application, and I'd like to have more. The current project would benefit from more programming help, and I would also like to develop a network of people interested in future projects.

I would like to see a real application in Ur/Web. There are many simple examples. I don't and wouldn't want to develop like that, writing raw HTML and SQL seems going backwards despite the incredible advances in consistency and correctness that Ur/Web offers.

I agree about the HTML part, but not so much about the SQL part. Personally I went back from all the nice abstractions to writing raw SQL, because I realized that this is the only way to really exploit the power of my database system (PostgreSQL) [1].

I agree. I find that SQL is the most natural language for expressing data reading and writing, at least for the web applications I write. The need to go through a less declarative interface (e.g., classic ORMs) would be a bug, not a feature, for me. (Though the online Ur/Web demos include type-safe ORM implemented as a library completely within the language!) As far as HTML templating goes, templates are easy to implement as functions within Ur. I understand that people unfamiliar with the language will want to see code examples before accepting this, but unfortunately I have none now.