Merge remote-tracking branch 'origin/stable-2.0'

module/system/base/ck.scm

@@ -0,0 +1,55 @@
+;;; ck, 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
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; 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 http://okmij.org/ftp/Scheme/macros.html#ck-macros for details.
+;;;
+
+(define-module (system base ck)
+  #:export (ck))
+
+(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))))