[Haskell-cafe] Ur tutorial, and a challenge

[Christopher Done]

On 19 July 2011 17:22, Adam Chlipala <adamc at impredicative.com> wrote:
>    http://www.impredicative.com/ur/demo/crud1.html
> The example involves a library component encapsulating functionality like
> that of Ruby on Rails's scaffolding: automatic generation of a standard
> web-based "admin interface" to an SQL database table.  The Ur/Web version
> uses static typing to guarantee that any applications generated by this
> component are free of injection attacks and other generic problems.  The
> guarantees apply both to app communication with server-side pieces (e.g.,
> static type-checking of SQL) and client-side pieces (e.g., static
> type-checking of HTML).  This is not done by type-checking individual
> invocations of the admin-interface component.  Rather, the component is
> checked at a static type which guarantees correct operation for
> _any_specialization_parameters_.
>
> So, the challenge is, can this functionality be implemented in Haskell (GHC
> extensions fair game, any web framework allowed)?

Is TemplateHaskell fair game? Because if so these problems are not
hard. Yesod employs static typing for templates. HaskellDB achieves
injectionless static type checking even without TemplateHaskell, and
templatepg has type safe SQL queries based on parsing the SQL itself
and inspecting the types involved by asking the PostgreSQL server
directly at compile time. This doesn't protect you from runtime
changes to the DB schema of course. I think there's a lot of
interesting work to be done based on inspecting the data base schema
by querying the database server and analyzing queries at compile time.
Ferry, anyone?

Statically avoiding SQL and HTML injection/type problems are trivial
problems that have been solved since forever ago, I don't think those
are Ur's best secret weapon (dependent types goes without saying). Of
Ur I particularly like that you can write Ur that will be compiled to
JS. That is something that is hard to do in Haskell right now (ghcjs
is a great base, but it's alpha). I don't anyone will spend time to
answer the crud challenge.

>   If so, how pretty is it?
> :)

Anything's gonna be prettier than what you've presented there. ;-)