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Import your CK macro into Guile?

From: Mark H Weaver
Subject: Import your CK macro into Guile?
Date: Fri, 09 Nov 2012 13:35:49 -0500

Hi Oleg,

I'd like to import your CK macro into Guile.  Would you be willing to
contribute it to Guile?  If so, please respond to the list to say so.
It's small enough (15 lines) that I guess we don't need papers.

Here's what I was hoping to add.  It's slightly modified to use an
internal helper macro instead of using the "arg" trick.

If not, I guess I can reinvent the wheel easily enough, but it seems
silly to do so.

What do you think?


;;; ck, an abstract machine to facilitate applicative-order macro
;;; programming

;;; Copyright (C) 2012 Free Software Foundation, Inc
;;; Copyright (C) 2009, 2011 Oleg Kiselyov
;;; This library is free software; you can redistribute it and/or
;;; modify it under the terms of the GNU Lesser General Public
;;; License as published by the Free Software Foundation; either
;;; version 3 of the License, or (at your option) any later version.
;;; This library is distributed in the hope that it will be useful,
;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;;; Lesser General Public License for more details.
;;; You should have received a copy of the GNU Lesser General Public
;;; License along with this library; if not, write to the Free Software
;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
;;; Originally written by Oleg Kiselyov and later contributed to Guile.
;;; Based on the CK machine introduced in:
;;; Matthias Felleisen and Daniel P. Friedman: Control operators, the
;;; SECD machine, and the lambda-calculus.  In Martin Wirsing, editor,
;;; Formal Description of Programming Concepts III, pages
;;; 193-217. Elsevier, Amsterdam, 1986.
;;; See for details.

(define-syntax ck
  (syntax-rules (quote)
    ((ck () 'v) v)                      ; yield the value on empty stack

    ((ck (((op ...) ea ...) . s) 'v) ; re-focus on the other argument, ea
     (ck-arg s (op ... 'v) ea ...))

    ((ck s (op ea ...))                ; Focus: handling an application;
     (ck-arg s (op) ea ...))))         ; check if args are values

(define-syntax ck-arg
  (syntax-rules (quote)
    ((ck-arg s (op va ...))             ; all arguments are evaluated,
     (op s va ...))                     ; do the redex

    ((ck-arg s (op ...) 'v ea1 ...)     ; optimization when the first ea
     (ck-arg s (op ... 'v) ea1 ...))    ; was already a value

    ((ck-arg s (op ...) ea ea1 ...)     ; focus on ea, to evaluate it
     (ck (((op ...) ea1 ...) . s) ea))))

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