@All, thanks for the interesting discussion.  Certainly gives me something to chew on.

Re-reading the responses, I see that, while I did sort-of say it, I didn't emphasize the point of this:

I have a PEG-syntax parser written in esrap.

I am binding at least two such parsers as reader-macros (not the normal kind of macro).

The first parser parses PEG syntax and creates an esrap program.

That esrap program, bound as a reader-macro, reads Prolog syntax and returns a bunch of lisp forms to the reader.

I have a file of code that contains both, lisp and Prolog syntax (cl-heredoc to switch between the syntaxes), e.g.

https://github.com/guitarvydas/paraphrase/blob/master/prolog.lisp

The parsers read characters, not forms.

(lisp)
#{ prolog(A,B,c) :- p1(A), p2(B,c). }
(morelisp)

I am making at least 2 assumptions:

1. That using different name spaces for the various parsers will help me preserve my sanity, (regression testing the PEG parser using itself brings me to the limits of my comprehension :-),

2. That a reader macro must return a single form.  I actually want to return a separate 'defun' for every prolog rule in the file. (Writing this, just now, makes me ask myself why I don't just put #{ ... } around every separate rule...)

(I even started fooling around with a Python syntax).

This line of thinking was inspired by the Gambit Scheme talk at ILC2010, where they showed inline infix mathematical expressions.

Thanks for your suggestions.