[web-devel] Hamlet variable interpolation syntax [previously: A few questions about Yesod]

Michael Snoyman michael at snoyman.com
Fri Dec 31 09:06:42 CET 2010

OK, I've put up a Wiki page[1] to discuss all of these changes. I
think I've put a summary of all the proposals brought up so far; if
anyone sees something missing, go ahead and edit it. Feel free to add
discussions inline (I think that's better than the discuss page for


[1] http://wiki.yesodweb.com/Hamlet%200.7%20changes

On Fri, Dec 31, 2010 at 9:18 AM, Aur Saraf <sonoflilit at gmail.com> wrote:
> While we're on the topic of breaking changes to Cassius:
> This week I've heard a lecture about Sass[1] and Less[2].
> [1] http://sass-lang.com/
> [2] http://lesscss.org/
> This is Sass:
> #navbar {
>  $navbar-width: 800px;
>  $items: 5;
>  $navbar-color: #ce4dd6;
>  width: $navbar-width;
>  border-bottom: 2px solid $navbar-color;
>  li {
>    float: left;
>    width: $navbar-width/$items - 10px;
>    background-color:
>      lighten($navbar-color, 20%);
>    &:hover {
>      background-color:
>        lighten($navbar-color, 10%);
>    }
>  }
> }
> Less is very similar.
> There are a few things I've learned:
> 1. Sass used to have a whitespace-is-significant syntax, but then
> switched to a CSS-superset syntax like Less, because it let people
> port their existing CSS by... doing nothing. Remembering all the times
> I've had to translate CSS to Cassius by hand, I think we should at
> least have a program like Python's 2to3 that translates a block of CSS
> to Cassius, if not move to the Sass syntax.
> 2. Sass supports some nifty features that I wished Cassius had
> (inheritance and mixins, numerical and color math, mixins with
> parameters which are like functions...)
> 3. Sass has Compass[3][4], which is sort of a standard library for
> CSS, with battle-tested classes that you can mix into your CSS for
> doing things you tend to do a lot and for doing things in a manner
> supported as cross-browser as possible. A lot of times, when writing
> CSS, I wish I'd have that. So that's another point for supporting Sass
> syntax.
> [3] http://compass-style.org/
> [4] An example (implementation of a) Compass function:
> @mixin hide-text {
>  $approximate_em_value: 12px / 1em;
>  $wider_than_any_screen: -9999em;
>  text-indent: $wider_than_any_screen * $approximate_em_value;
>  overflow: hidden;
>  text-align: left; }
> To support Sass syntax, we could either parse it, which is as
> complicated as parsing CSS, and then reimplement Sass's logic, which
> isn't very hard but would require us to chase it as it changes, or we
> could use a plaintext-with-variable-interpolation parser and feed that
> to the Sass toolset (without any harm to the type safety of the code,
> and with options to run Sass either in compile-time or in run-time,
> but it would require the user to install ruby and Sass).
> Of course, Sass support could be added quite easily on a per-project
> basis (and I just might do that soon for one of mine), but as I've
> showed, there are some serious advantages to making it default.
>  -- Aur

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