The other matter of style is whether the order of the code matches the order in which the user interacts with it.

The three steps in user experience order:

  first:  a form to accept input,
  second: a link to click
  third:  a printout of the input

Here are the orders used in code:

  Ruby+sinatra:   third, first, second
  arc version 1:  third, second, first (original)
  arc version 2:  second, third, first (May 2009)
  Haskell+custom: first, second, third

Interesting results, I think Haskell wins here. Though technically it fails the challenge (the arc version 2 example fails too) since the supporting library was written after the challenge was considered by the author of the example.

The Perl+Continuity solution also uses "first, second & third" style and does it nicely without sessions and adheres to challenge by being an established library: http://arclanguage.org/item?id=805

Here is a version using the HTML::AsSubs module:

    use Continuity;
    use HTML::AsSubs;
    Continuity->new->loop; # This starts the webserver

    sub main {
        my $request = shift;
        my $p = 'foo';

        $request->print( aform( $p )->as_HTML );
        my $foo = $request->next->param( $p );
        $request->print( w_link()->as_HTML );
        $request->next->print( "You said: $foo" );
    }

    sub aform {
        form( 
            input( { type => 'text', name => $_[0] } ), 
            input( { type => 'submit'} )
        );
    }

    sub w_link { a( { href => '.' }, 'Click Here' ) }