Though I have precious little expertise in this area, I've noticed this seems to be something of a hobby of the redoubtable LanX ... at least, he often mentions little languages -- for example adding the caveat "when designing syntactic sugar and/or DSLs its useful to leave the parentheses off" in his reply to my stylistic advice on calling functions with parens.

Some random nodes from super-searching follow in case they are of use:

• Combining Import and Source-Filter to implement Syntactic Macro mechanism by LanX (2019)
• Are there any modules using source filter to capture code? by LanX (2017)
• sourcefilter with complete parser? by LanX (2013) (asked about parsing a JS or LISP or a pedantic Perl sub dialect)

• Is Devel::Declare really so much less evil than source filters? by moritz (2010)

• "Current position" of source filter input relative to original input by Corion (2011)
• source filtering and mod_perl2 by Logicus (2011)

• Source filters in eval/require by liz (2003)
• What do you know about source filters? by Beatnik (2002)