thank you both, but I think I failed to express myself: what I meant to ask is: how is this better than other xml based templates, such as wicket, TAL, Kid, Genshi etc.

I would be led to understand, given your comments, that Heist does not allow control structures in the templates, but looking at some snap code[0] it would seem iteration is right there. Which makes sense I guess.

Or am I missing something, and there is a fundamental difference between Heist's

    <posts:reverseChronological>
      <a href="${post:url}">stuff</a>
    </posts:reverseChronological>

and, say, Genshi's

   <a py:for="post in reverseChronological"  href="${post:url}">stuff</a>

Is the difference, and thus your preference, in the fact that posts:reverseChronological works more like a function call taking the content as argument, rather than a "classic" loop?

[0] https://github.com/snapframework/snap-website/blob/master/bl...

I think the difference is that Genshi's py:for appears to be a construct provided by the template system. In Heist, posts:reverseChronological, like you say, is just a function call. Looping doesn't happen in the template, it happens on the Haskell side. Genshi has to have a different construct py:if for conditionals. Heist doesn't need another construct. A function call serves both purposes. This has several positive effects. First, it means Heist's core is simpler since it only has one fundamental abstraction that has enough expressive power for implementing all of Genshi's special case keywords. And second, I think it gives a clearer separation between logic and view.

>how is this better than other xml based templates, such as wicket, TAL, Kid, Genshi etc.

I don't think it is. To me it is just the haskell template engine in that style (which is the style I prefer). That style of template engine is the minority, so most comparisons are vs either mixed style (php/asp/jsp/rails) or vs custom syntaxes (mustache, haml, etc). What is good about heist certainly applies to similar template engines like lifts, zopes, etc.