AIUI, this was the original genesis of Lisp - the S-expressions were supposed to be an internal abstract representation, and programmers would write "M-expressi

AIUI, this was the original genesis of Lisp - the S-expressions were supposed to be an internal abstract representation, and programmers would write "M-expressions" in a language a bit like Fortran. But everyone involved in Lisp realised you could just write S-expressions directly, and never got round to defining the M-expression syntax. More recently, the GNU scheme project, Guile, had people working on pluggable syntax translators that would allow you to write Guile programs in TCL or JavaScript syntax, but AFAIK that project never produced anything completely usable.