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herbalizer

A HAML to ERB translator, written in Haskell.

This program converts HAML templates to ERB.

Why

A lot of people prefer HAML to ERB. But not everyone, and not for every circumstance. ERB is simpler, easier to remember the rules for, and more accessible to anyone familiar with HTML. ERB templates are easier to teach to beginners and easier to collaborate on with a wider range of people, like designers. And for some people ERB is easier on the eyes.

As far as I know, there is no other good tool to convert HAML to ERB. To quote HAML maintainer Nathan Weizenbaum:

No, no such tool exists. In fact, it's not possible to make without parsing Ruby code - Haml supports several constructs, such as = with a block and comments within Ruby code, that ERB doesn't. It might be possible to modify the Haml engine to convert a fairly large subset of Haml to ERB, but it would take considerable work to even get to an imperfect implementation. source

However, with Haskell, it is possible to write a pretty good parser-translator for HAML markup without incorporating a full-blown Ruby parser.

Requirements

The GHC Platform, unless you're using a precompiled binary.

Install

cabal update
cabal install herbalizer

Quick setup for Mac OS X Users

I've precompiled the executable for OS X (10.8). You can download it and chmod +x it:

wget http://openmbta.org/herbalizer
chmod +x herbalizer

And then put it on your PATH.

OSX - Add to Path

sudo /etc/paths

You will need to reload your terminal for path to update. Verify the new path with...

echo $PATH | grep Haskell

You can also compile programs using cabal. If you are programming in Haskell with your development system setup with cabal....

Add this to your ~/.bash_profile

export PATH="$HOME/Library/Haskell/bin:$PATH"

source ~/.bash_profile

Usage

herbalizer < test.haml

Simple way to save file

herbalizer < test.haml > outputfile.html.erb

You can also pass filenames as arguments:

herbalizer test.haml

Caveats

herbalizer can deal with the most commonly used features of HAML's syntax. Mainly, it will handle the widely used HAML syntax features for tags, classes, ids, attributes, Ruby blocks and expressions, and inline <script> content.

I wrote it so that I could automate at least 90% of work I need to do to translate HAML templates to ERB. YMMV.

herbalizer can't yet recognize some less commonly used HAML constructs such as

  1. HTML-style () attributes e.g. %a(title=@title href=ahref)
  2. :class and :id attributes specified as a Ruby array, e.g. %div{:id => [@item.type, @item.number], :class => [@item.type, @item.urgency]}
  3. Filters besides :javascript and :erb; these are just rendered inside pseudo-tags named after the filter
  4. Whitespace removal sytnax
  5. Object reference syntax
  6. Escaping HTML &= syntax
  7. Multiline | syntax
  8. Ruby Interpolation #{} within plain body text; passed through
  9. Conditional /[] comments; passed through; normal / comments OK
  10. HAML Comments (#-) not processed
  11. XML Doctype (!!! XML) declarations; HTML Doctype declarations are supported
  12. Ternary Ruby expressions in attribute values are not handled robustly; surround these with parentheses
  13. Nested attribute hash expressions e.g. {:data => {:send => false, :width => 100}} are not processable

Maybe herbalizer will cover more of these edge cases over time. Let me know in a GitHub issue if you have a particular need. I'll try to write a patch.

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