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

2010/12/30 Michael Snoyman :

On Thu, Dec 30, 2010 at 3:31 PM, Iustin Pop wrote:

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On Thu, Dec 30, 2010 at 03:09:16PM +0200, Michael Snoyman wrote:

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Very good questions, answers below.

On Thu, Dec 30, 2010 at 1:01 PM, Iustin Pop wrote:

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Hi all,

I just started looking at Yesod and its associated libs (hamlet, etc.) and it is very interesting, thanks.

However, I'm confused by a few things and the docs are not helping, so please bear my beginner questions.

First: hamlet uses '.' as function application, instead of the usual space. How can I then use a qualified name (e.g. Data.List.nub)? If I use it normally, it errors out on me. Must be something very trivial but I cannot find a way.

Hamlet uses both '.' and space as function application, and therefore qualified names are not supported. I work around this usually by creating an alias for the function I want locally. I know this can be inelegant; if you have any ideas, I'm all ears.

Yep, that's what I'm using too now, but it becomes cumbersome quickly, especially when using records…

I'm not sure what was the original impetus to use . (too) as function application if space is accepted too. I'm thinking reverting that decision would make the code look more like regular Haskell.

A simpler alternative (not sure if easily doable) would be to allow escaping of the dot, e.g. $Data\.List\.nub.mylist$; it's ugly, but…

It actually went the other way: period first, and space added by request. Originally, Hamlet variables were not directly mapped to Haskell function calls. Instead, it was meant to parallel variable lookup in common template languages from the object-oriented world. Another impetus is because of statements like forall and maybe:

$forall allPeople.myFamily person    %li $person name$

This can also be written as

$forall (allPeople myFamily) person

You could argue that the latter is more legible; my problem with the space is for cases with more than two functions in the chain. $foo bar baz$ gets converted to the Haskell code "foo (bar baz)".

I'll admit that this whole situation bothers me as well. Hamlet 0.7 is currently in the works, and I don't mind introducing some major changes. I think this issue deserves some attention: what does everyone else think? Maybe we should start a separate thread to discuss this issue in particular.

Would there be a problem with removing the dot syntax entirely and just having regular Haskell syntax for variable interpretation? That might be more flexible and easier to learn. Alexander