As part of the process of getting IDL recognized by GitHub, I had to add IDL support to Pygments, a popular syntax highlighter supporting many languages. This allows generating syntax highlighting of IDL code.
pip to install Pygments:
$ pip install Pygments
pygmentize to generate output:
$ pygmentize -O full,style=colorful -f html -o mg_repmat.html mg_repmat.pro
This produces the output below:
Here is the full output. This is obviously not perfect (I just wanted GitHub to recognize the language as IDL).