|author||Sean Whitton <email@example.com>||2022-05-08 13:41:12 -0700|
|committer||Sean Whitton <firstname.lastname@example.org>||2022-05-08 13:41:12 -0700|
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+I recently [[released Consfigurator 1.0.0|blog/entry/consfigurator_1.0.0]] and
+I'm now returning to my Common Lisp reading. Building Consfigurator involved
+the ad hoc development of a cross between a Haskell-style functional DSL and a
+Lisp-style macro DSL. I am hoping that it will be easier to retain lessons
+about building these DSLs more systematically, and making better use of
+macros, by finishing my studying of macrology books and papers only after
+having completed the ad hoc DSL. Here's my current list:
+- Finishing off *On Lisp* and *Let Over Lambda*.
+- Richard C. Waters. 1993. "Macroexpand-All: an example of a simple lisp code
+ walker." In *Newsletter ACM SIGPLAN Lisp Pointers 6 (1)*.
+- [Naive vs. proper code-walking](http://christophe.rhodes.io/notes/blog/posts/2014/naive_vs_proper_code-walking/).
+- Michael Raskin. 2017. "Writing a best-effort portable code walker in
+ Common Lisp." In *Proceedings of 10th European Lisp Symposium (ELS2017)*.
+- Cullpepper et. al. 2019. "From Macros to DSLs: The Evolution of Racket".
+ *Summet of Advances in Programming Languages*.
+One thing that I would like to understand better is the place of code walking
+in macro programming. The Raskin paper explains that it is not possible to
+write a fully correct code walker in ANSI CL. [Consfigurator currently uses
+Raskin's best-effort portable code
+*Common Lisp: The Language 2* includes a few additional functions which didn't
+make it into the ANSI standard that would make it possible to write a fully
+correct code walker, and most implementations of CL provide them under one
+name or another. So one possibility is to write a code walker in terms of
+ANSI CL + those few additional functions, and then use a portability layer to
+get access to those functions on different implementations
+However, both *On Lisp* and *Let Over Lambda*, the two most substantive texts
+on CL macrology, both explicitly put code walking out-of-scope. I am led to
+wonder: does the Zen of Common Lisp-style macrology involve doing without code
+walking? One key idea with macros is to productively blur the distinction
+between designing languages and writing code in those languages. If your
+macros require code walking, have you perhaps ended up too far to the side of
+designing whole languages? Should you perhaps rework things so as not to
+require the code walking? Then it would matter less that those parts of CLtL2
+didn't make it into ANSI. Graham notes in ch. 17 of *On Lisp* that read
+macros are technically more powerful than defmacro because they can do
+everything that defmacro can and more. But it would be a similar sort of
+mistake to conclude that Lisp is about read macros rather than defmacro.
+There might be some connection between arguments for and against avoiding code
+walking in macro programming and the maintainance of homoiconicity. One
+extant CL code walker, hu.dwim.walker, works by converting back and forth
+between conses and CLOS objects (Raskin's best-effort code walker has a more
+minimal interface), and hygienic macro systems in Scheme similarly trade away
+homoiconicity for additional metadata (one Lisp programmer I know says this is
+an important sense in which Scheme could be considered not a Lisp). Perhaps
+arguments against involving much code walking in macro programming are
+equivalent to arguments against Racket's idea of language-oriented
+programming. When Racket's designers say that Racket's macro system is "more
+powerful" than CL's, they would be right in the sense that the system can do
+all that defmacro can do and more, but wrong if indeed the activity of macro
+programming is more powerful when kept further away from language design.
+Anyway, these are some hypotheses I am hoping to develop some more concrete
+ideas about in my reading.