M4 syntax looks that way because it has to work for arbitrary text files.

Quotes can be redefined to an arbitrary string

   changequote(`[[[', `]]]')

And some editor give you syntax highlighting.

> M4 syntax looks that way because it has to work for arbitrary text files.

That seems like an odd assertion given the existence of other templating systems which have friendlier syntax while being capable of generating arbitrary output. Is there a reason why you think on the M4 approach is valid?

Most templating systems work in combination with an external program written in a high-level language, e.g. Ruby for Liquid or Python for jinja2. m4 does not.

And m4 works in combination with a bunch of C code. Virtually any system with m4 can come with an interpreter for a higher level language without running out of space (I can't imagine many uses for m4 at runtime on systems where, say, a perl interpreter wouldn't fit). Why is relying on such a runtime a problem?

No, m4 is written in C but it is autonomous. Liquid needs something like Jekyll around it.

What does “autonomous” mean? There are a ton of template engines that don’t depend on a parent framework, there is no reason you can’t implement all features in C.

Something like mustache for example, which has a C implementation that includes support for includes/partials: http://mustache.github.io/mustache.5.html

Jinja2 is an API and it needs a Python program to determine the values for the substitution variable and invoke the template engine. In contrast the M4 executable is the engine.