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Re: [Haskell-cafe] ANNOUNCE: Bravo-0.1.0

Subject: Re: [Haskell-cafe] ANNOUNCE: Bravo-0.1.0
From: Matthias Reisner
Date: Fri, 12 Mar 2010 05:37:38 +0100
Hi Michael

Am 12.03.2010 01:33 schrieb Michael Snoyman:
I'll need to look into the library a bit more to get a better idea, but it
seems like Bravo could work for my needs. One thing that concerns me is your
comment that it allows embedding of Haskell expressions. In general, I try
to keep a strict separation between login and presentation: can you explain
exactly what type of expressions can be embedded?

This is really one disadvantage of the current Bravo version I'm worrying about too. At the moment you can insert arbitrary Haskell expressions, so no one prevents the template writer from inserting expressions like `unsafePerformIO launchAtomicMissile >> return ""'. Some kind of security mechanism will definitely be included in future releases, but I'm not sure in what way at the moment. I thought about passing a list of permitted function names to the template creation function and then failing with an error if any other functions are used.

Also, while looking through the example, it looks like the library is making
some automatic translations, like firstName -> userFirstName and user ->
users. I've found these kinds of mappings to be brittle in the past; can you
explain how this is done (or if I'm simply missing something obvious)?

Bravo creates a data type per template, where the default naming scheme for the data type/constructor name is "name" -> "TplName". For each template variable a record field is created; for a template "temp" and a variable "var" the name will be "tempVar". Have a look at the `mkTemplatesWithOptions' and `mkTemplatesFromFileWithOptions' functions, that allow you to customize this naming scheme.

Finally, I can't seem to get it to compile on 6.12. Any chance of getting a
version out that supports it?

The problem seems to be haskell-src-meta, that doesn't like template-haskell-2.4, and on the other side I can't get build template-haskell < 2.4 with GHC-6.12. So I will contact Matt Morrow, the maintainer of haskell-src-meta, and see if he can fix it.




On Wed, Mar 10, 2010 at 8:46 PM, Matthias Reisner <
[email protected]> wrote:


I'm pleased to announce the first release of Bravo, a static text template
generation library, on Hackage: http://hackage.haskell.org/package/Bravo.

Bravo is a text template library that provides parsing and generation of
templates at compile time. Templates can be read from strings or files and
for each a new record data type is created, allowing convenient access to
all template variables in a type-safe manner. Since all templates are
processed at compile time, no extra file access or error handling at runtime
is necessary.

Bravo is inspired by the PHP template engine Smarty and the Haskell
template library chunks. Compared to chunks, Bravo provides additional
features like conditional template evaluation, embedding of Haskell
expressions and customized data type generation. I'm going to add further
information to the HaskellWiki page (
http://www.haskell.org/haskellwiki/Bravo) later.

Bravo is still highly experimental and not well-tested, so bug reports and
additional feedback are very welcome. I'd also like to hear if you feel the
package dependencies are to restrictive.


Matthias Reisner
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