Re: [web-devel] [Yesod] Creating a static link

Dmitry Kurochkin disse:

On Sun, 13 Feb 2011 13:26:24 -0200, Rafael Cunha de Almeida wrote:

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Michael Snoyman disse:

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You could go either way on that one. The content of an interpolation is specifically *not* a fully-powered Haskell expression.

Why is that? I have a little experience with RoR, there I could do something like this:

- @people.each do |person| = person.name

I think you don't want to have a fully-powered Haskell expression to avoid people adding too much code to the view (thinking in MVC pattern). However, it's not like people can't do it just because it's a little harder. Meanwhile, there are a lot of useful things that could be done if all (or most) haskell syntax was allowed to be interpolated.

Instead of having special syntax like $forall, wouldn't it be better to just provide monad tranformers to allow for those sort of loops? Something like Control.Monad.LoopWhile module provides. That way hamlet would need only to provide a ${} syntax that allow for adding haskell code which will be evaluated but won't print anything to the site. That way things could work a lot like in ruby, which I think makes things a lot simpler.

Allowing for a new sort of interpolation and any sort of haskell expression to be interpolated, hamlet wouldn't need to create its own flow control statements. The user could write their views freely using only haskell syntax when code logic is required.

I join the question! I have some style-related constants in Style module, e.g. sizes and colors. Then I want to do computations using these constants in Cassius, something similar to SCSS. E.g. width: #{Style.width1 + Style.width2} (not talking about appending "px" suffix for now). Currently, because of artificial limitations on Hamlet interpolations, I have to define (plus = (+)) (minus = (-)) and so on. Would be nice if it allowed full-featured Haskell.

I had a similar problem. I solved it by creating a CssDefinitions module. The good thing about it is that I can share it among all widgets of my application. That way I have a single place to configure all layout constants of the entire site. It might be a bad solution for a big site with a lot of CSSs, widgets, etc. But for my use case it's completely manageble.