This is <i>roughly</i> the same problem as syntactical macros in non-Lisp syntax languages.<p>There needs to be a way to indicate a "hole" (metavariable/unquote) in the syntax tree, and depending on the complexity of the language's grammar, that might be somewhat difficult, eg. in C++ having a hole for a type declaration runs into the common ambiguity between declarations (constructor calls) and expressions (regular calls).
This needs to be worked around by eg. having multiple types of holes to disambiguate...<p>For the article, the idea of using an "any" prefix on identifiers instead of eg. operators such as ` , ... (Lisp macros) is an interesting solution, as it does not require extending the grammar of the language... although it's not applicable in all situations (eg. for matching grammar elements where identifiers are not allowed).
For a very regular language like Smalltalk though, it's pretty good.<p>Grammar-based rewriting has a long line of history and research, so there's a deep well of knowledge to be mined if you feel like hitting up Google Scholar...<p>For modern implementations, there's eg. ast-grep and semgrep:
<a href="https://ast-grep.github.io/" rel="nofollow">https://ast-grep.github.io/</a>
<a href="https://semgrep.dev/docs/writing-rules/pattern-syntax" rel="nofollow">https://semgrep.dev/docs/writing-rules/pattern-syntax</a>