[Guile-commits] GNU Guile branch, master, updated. release_1-9-15-18-g15b06ca

[Andy Wingo]

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- Log -----------------------------------------------------------------
commit 15b06ca9cee69509fef83928fa492c51c8292bb7
Author: Andy Wingo <address@hidden>
Date:   Wed Feb 9 20:54:36 2011 +0100

    readline uses define-once
    
    * guile-readline/ice-9/readline.scm: Use define-once.

commit c5f30c4cba204114008b8ddc8ecea5a081be69b7
Author: Andy Wingo <address@hidden>
Date:   Wed Feb 9 20:54:22 2011 +0100

    add define-once
    
    * module/ice-9/boot-9.scm (define-once): New syntax.
    
    * doc/ref/api-binding.texi (Top Level):
    * NEWS: Add notes about define-once.

-----------------------------------------------------------------------

Summary of changes:
 NEWS                              |    5 +++++
 doc/ref/api-binding.texi          |   19 ++++++++++++++++++-
 guile-readline/ice-9/readline.scm |   20 ++++++++++----------
 module/ice-9/boot-9.scm           |    5 +++++
 4 files changed, 38 insertions(+), 11 deletions(-)

diff --git a/NEWS b/NEWS
index 27b52ae..7912259 100644
--- a/NEWS
+++ b/NEWS
@@ -10,6 +10,11 @@ latest prerelease, and a full NEWS corresponding to 1.8 -> 
2.0.
 
 Changes since the 1.9.15 prerelease:
 
+** New syntax: define-once
+
+`define-once' is like Lisp's `defvar': it creates a toplevel binding,
+but only if one does not exist already.
+
 ** Improved exactness handling for complex number parsing
 
 When parsing non-real complex numbers, exactness specifiers are now
diff --git a/doc/ref/api-binding.texi b/doc/ref/api-binding.texi
index 60af456..c97ae73 100644
--- a/doc/ref/api-binding.texi
+++ b/doc/ref/api-binding.texi
@@ -1,6 +1,6 @@
 @c -*-texinfo-*-
 @c This is part of the GNU Guile Reference Manual.
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009, 
2010
address@hidden Copyright (C)  1996, 1997, 2000, 2001, 2002, 2003, 2004, 2009, 
2010, 2011
 @c   Free Software Foundation, Inc.
 @c See the file guile.texi for copying conditions.
 
@@ -88,6 +88,23 @@ longer visible.
 Attention: Scheme definitions inside local binding constructs
 (@pxref{Local Bindings}) act differently (@pxref{Internal Definitions}).
 
+Many people end up in a development style of adding and changing
+definitions at runtime, building out their program without restarting
+it.  (You can do this using @code{reload-module}, the @code{reload} REPL
+command, the @code{load} procedure, or even just pasting code into a
+REPL.)  If you are one of these people, you will find that sometimes you
+there are some variables that you @emph{don't} want to redefine all the
+time.  For these, use @code{define-once}.
+
address@hidden defvar
address@hidden {Scheme Syntax} define-once name value
+Create a top level variable named @var{name} with value @var{value}, but
+only if @var{name} is not already bound in the current module.
address@hidden deffn
+
+Old Lispers probably know @code{define-once} under its Lisp name,
address@hidden
+
 
 @node Local Bindings
 @subsection Local Variable Bindings
diff --git a/guile-readline/ice-9/readline.scm 
b/guile-readline/ice-9/readline.scm
index 36f805f..a9f7cdc 100644
--- a/guile-readline/ice-9/readline.scm
+++ b/guile-readline/ice-9/readline.scm
@@ -1,6 +1,6 @@
 ;;;; readline.scm --- support functions for command-line editing
 ;;;;
-;;;;   Copyright (C) 1997, 1999, 2000, 2001, 2002, 2006, 2009, 2010 Free 
Software Foundation, Inc.
+;;;;   Copyright (C) 1997, 1999, 2000, 2001, 2002, 2006, 2009, 2010, 2011 Free 
Software Foundation, Inc.
 ;;;; 
 ;;;; This program is free software; you can redistribute it and/or modify
 ;;;; it under the terms of the GNU General Public License as published by
@@ -73,11 +73,11 @@
 ;;; Dirk:FIXME:: If the-readline-port, input-port or output-port are closed,
 ;;; guile will enter an endless loop or crash.
 
-(define new-input-prompt "")
-(define continuation-prompt "")
-(define input-port (current-input-port))
-(define output-port (current-output-port))
-(define read-hook #f)
+(define-once new-input-prompt "")
+(define-once continuation-prompt "")
+(define-once input-port (current-input-port))
+(define-once output-port (current-output-port))
+(define-once read-hook #f)
 
 (define (make-readline-port)
   (let ((history-buffer #f))
@@ -115,10 +115,10 @@
 ;;; everything except the prompt.  And don't forget the
 ;;; compile/load/run phase distinctions.  Also, the readline library
 ;;; isn't reentrant.
-(define the-readline-port #f)
+(define-once the-readline-port #f)
 
-(define history-variable "GUILE_HISTORY")
-(define history-file (string-append (getenv "HOME") "/.guile_history"))
+(define-once history-variable "GUILE_HISTORY")
+(define-once history-file (string-append (getenv "HOME") "/.guile_history"))
 
 (define-public readline-port
   (let ((do (lambda (r/w)
@@ -215,7 +215,7 @@
        (lambda ()
          (set! *readline-completion-function* old-completer)))))
 
-(define readline-repl-reader
+(define-once readline-repl-reader
   (let ((boot-9-repl-reader repl-reader))
     (lambda* (repl-prompt #:optional (reader (fluid-ref current-reader)))
       (let ((port (current-input-port)))
diff --git a/module/ice-9/boot-9.scm b/module/ice-9/boot-9.scm
index fe7f2b2..f706a71 100644
--- a/module/ice-9/boot-9.scm
+++ b/module/ice-9/boot-9.scm
@@ -473,6 +473,11 @@ If there is no handler at all, Guile prints an error and 
then exits."
        (with-syntax ((s (datum->syntax x (syntax-source x))))
          #''s)))))
 
+(define-syntax define-once
+  (syntax-rules ()
+    ((_ sym val)
+     (define sym
+       (if (module-locally-bound? (current-module) 'sym) sym val)))))
 
 
 


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