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Hardcode Haml - Haml for Hardcore Coders (and Embedded devices)

Compiling Haml markup/templates to program code.

Warning: There are still some language features missing. The TODO section is an imcomplete documentation of the the parts I am aware of.


Most template engines for compiled and statically typed languages (like C and C++) are only able to do simple search and replace jobs for given values. Having used template engines in script languages like Ruby, Python or Java Script makes returning to those template engines hard. This is where Hardcode Haml comes into play.

Haml was first implemented in ruby and got ported to multiple other languages. It compines the ability to replace parts of your markup with values calculated at runtime (even allowing evaluation of code directly from the markup) and additionally replaces XML with more writeable and readable markup.

This project turns Haml markup into program code. Therefore the markup gets parsed and processed before runtime and maybe even optimized by your compiler. Therefore execution time, memory footprint and file size on the target device should be superior to other approaches. The drawback is, that your templates are compiled in your binary and you can't edit them on the target system.

The language modules will generate a function which, when executed, will output the generated XML markup into a stream. The parameters of the function can be referenced directly from within the template. Haml contains syntax elements which let you print out evaluated code and even pass code directly to the generated code. Loops and other control flow elements can be used to repeat blocks or conditionally display them.

To fullfill the needs of the target languages, Haml syntax has to be extended. We need a way to specify the name and type of the parameters given to the template. Additionally most languages need a way to execute code before the function declaration (e.g. to include headers).


Hardcode Haml is used in at least one production environment (in which I am involved). The development is driven by this project as we find bugs and important missing features. I am confident that Hardcode Haml in its current state is stable and comprehensive enough to be useful in other projects.

If you are missing a useful feature or find a bug please file an issue on Github. Also feel free to contact me there if you have any questions.

Supported Languages

Output can currently be generated in several languages

  • C++ (using ostream)
  • C (using fputs())
  • python (using Pythons file objects)

Other languages can be implemented with ease. All language implementations are currently smaller than 100 lines (including whitespaces).

Haml passes code directly to the underlying language, so the language modules won't be interchangable without replacing some code in your templates.

Hardcode Haml Dialect

Some syntax changes were neccessary to adopt Haml to the target languages.


As languages like C and C++ do not have tightly built-in dictionary types using those does not come natural in these languages. I therefore decided to use a more native approach to pass the data into the template: Function parameters. To declare those the Haml syntax has to be extended:

? int a, std::string b

The ? declares the parameters passed to the templates and starts the actual template. An implicit ? at the start of the document is assumed if there is none explicit declaration.

Introducing this operator has another advantage: It is possible to introduce code which will be placed outside the actual function processing the template. Simply write this code before the ? declaration. The way this code behaves depends on the language you are using. In C/C++ this code will be added to the header which enables you to include files and declare types used in your template.

Boolean attributes

Boolean attributes are implicit in ruby and detected at runtime. Hardcode Haml tries to do as much as possible in the parser and avoids complexity in the language modules. Another problem is that not all target languages are able to determine whether an expression evaluates to a boolean. Hardcode Haml therefore extends the syntax with the '?=' and '?=>' operators for attributes.

Boolean attributes are useful for radiobuttons, checkboxes and select elements. Simply write:

%input(type="radio" checked?=foo)

... or ...

%input(type="radio"){"checked" ?=> foo}

This code evaluates to the following (X)HTML when foo is true:

<input type="radio" checked="checked">

... and when foo is false to:

<input type="radio">


There is an example in the Wiki.



  • correct scoping according to indent
  • implement most common syntax/language elements (see below)
  • ...
  • document implemented functionality and introduced syntax extensions of Haml
  • clean up the code (especially in the parser)
  • target language site helper
  • ...

Syntax/Language Elements

Must have

  • entity escape (static, dynamic?)
  • filters (infrastructure, some filters)

May have

  • whitespace removal (< and >)
  • conditional comments /[] (only needed to support IE afaik)
  • whitespace preservation
  • escaping/unescaping html in evaluations

Won't implement (in the near future)

  • object reference [] (too close to the target language)



Haml for hardcore coders (and C++/C/... projects)







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