[Ur] Announcing jsMove

[Adam Chlipala]

Thanks for the nice example!

I think the mouse/key event handler changes I announced yesterday might 
make some (but definitely not all) of your FFI work redundant.

Why does jsMove.urs include type definitions?

I notice many redundant parentheses in jsMove.ur, which is 
understandable for someone new to ML-style syntax (if you are?), but 
which still confuses me, since I assume parens are there for a reason. ;)

You define a function [showXY] that would be an excellent candidate for 
a [show] type class instance, so that you could afterward call merely 
[show] instead of [showXY].

There is a [source] holding a [string] that gives instructions for the 
user.  Currently, an 'onload' handler computes this string imperatively 
and stores it in the [source].  A more idiomatic Ur/Web approach would 
be to code the instructions part of the page as a <dyn> that refers 
directly to the underlying data sources (in this case, [mouseOn] and 
[clickToMove]).  This also saves you some code duplication, as currently 
you recompute the instructions in the same way in multiple locations.

Clearly it is worth defining a function for the pattern [x <- signal x; 
return <xml>{[x]}</xml>], in some common library. :-)

You use the constructor [Cons] directly in one place.  I prefer the 
infix operator [::] for that.

Timothy Beyer wrote:
> I recently implemented a simple Ur/Web application "jsMove" which draws a
> circle to the screen.  The circle may be moved interactively via keyboard/mouse
> or touchscreen, depending on the selected URL (main or main_touch).  It uses
> the Ur/Web JavaScript FFI extensively for graphics (Raphaël) and for several
> additional event handlers.
>
> It is mainly targeted towards people who are completely new to Ur/Web and don't
> understand how to use the JavaScript FFI very well, or people who want to write
> non-traditional web applications (eg. games, desktop style applications) in a
> browser.
>
> Keep in mind that the code is ugly because I haven't mastered the type system
> yet, so any critiques are welcome.  There are also currently some issues with
> pressing the buttons with the mouse, but for the most part the code works very
> well and could likely be useful to others.
>
> The complete source code is available:
> http://chiselapp.com/user/beyert/repository/urweb_examples/urweb_examples