Hey all,
An often-mentioned "cool feature" for Hamlet would be to support runtime parsing/rendering of templates. Currently, the only supported method is quasi-quoting a template and thereby have it parsed into Haskell code at compile time. In my opinion, this is definitely the preferred way of using Hamlet, as it gives you very solid compile-time guarantees of correct syntax and type safety. Nonetheless, there are some use cases (static site generation via Hakyll, a hamlet-to-html tool, etc) that would really benefit from runtime parsing.
It turns out this is pretty simple to add, except for one thing: I can't figure out a good API for passing in variables for a template. Hamlet templates have essentially four different datatypes they recognize:
* Html
* Some URL data type
* That same URL datatype along with a [(String, String)] to represent query-string parameters
* A Hamlet template
In addition, $forall and $maybe need lists and Maybe values, respectively. Variable lookup is handled by a tree, which allows you to express arbitrary function application. $if requires Bools.
So the question is, what should an API look like? The parse function is fairly straight-forward:
parseHamletRT :: HamletSettings -> String -> Either HamletException HamletRT
However, the render function is more complicated. I've toyed with a few possible ideas:
* Use the data-object package with some complicated HamletData datatype.
* Just do the complicated HamletData datatype.
* Type lookup functions as parameters.
* Disallow most of the more complicated features in Hamlet, like URL and subtemplates, and just allow dollar-sign interpolation with $forall and $if. That tree datatype for variable names could be collapsed into a [String].
Thoughts on the matter are welcome, as well as sample use cases you have for such a function.
Michael