prompt around REPL evaluations, and around `guile' program invocation

* module/ice-9/control.scm (%): Add a single-argument case, which
  instates a default prompt with a default handler.

* libguile/script.c (scm_compile_shell_switches): Wrap user programs in
  a default prompt.

* module/system/repl/common.scm (repl-eval): REPL expressions are user
  programs too; wrap each one in a default prompt.

libguile/script.c

@@ -1,4 +1,4 @@
-/* Copyright (C) 1994, 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.
+/* Copyright (C) 1994, 1995, 1996, 1997, 1998, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
  * 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
@@ -740,6 +740,13 @@ scm_compile_shell_switches (int argc, char **argv)
   {
     SCM val = scm_cons (sym_begin, tail);
 
+    /* Wrap the expression in a prompt. */
+    val = scm_list_2 (scm_list_3 (scm_sym_at,
+                                      scm_list_2 (scm_from_locale_symbol ("ice-9"),
+                                                  scm_from_locale_symbol ("control")),
+                                      scm_from_locale_symbol ("%")),
+                      val);
+
 #if 0
     scm_write (val, SCM_UNDEFINED);
     scm_newline (SCM_UNDEFINED);

module/ice-9/control.scm

@@ -28,6 +28,10 @@
 
 (define-syntax %
   (syntax-rules ()
+    ((_ expr)
+     (call-with-prompt (default-prompt-tag)
+                       (lambda () expr)
+                       default-prompt-handler))
     ((_ expr handler)
      (call-with-prompt (default-prompt-tag)
                        (lambda () expr)
@@ -36,3 +40,17 @@
      (call-with-prompt tag
                        (lambda () expr)
                        handler))))
+
+;; Each prompt tag has a type -- an expected set of arguments, and an unwritten
+;; contract of what its handler will do on an abort. In the case of the default
+;; prompt tag, we could choose to return values, exit nonlocally, or punt to the
+;; user.
+;;
+;; We choose the latter, by requiring that the user return one value, a
+;; procedure, to an abort to the prompt tag. That argument is then invoked with
+;; the continuation as an argument, within a reinstated default prompt. In this
+;; way the return value(s) from a default prompt are under the user's control.
+(define (default-prompt-handler k proc)
+  (% (default-prompt-tag)
+     (proc k)
+     default-prompt-handler))

module/system/repl/common.scm

@@ -1,6 +1,6 @@
 ;;; Repl common routines
 
-;; Copyright (C) 2001, 2008, 2009 Free Software Foundation, Inc.
+;; Copyright (C) 2001, 2008, 2009, 2010 Free Software Foundation, Inc.
 
 ;;; This library is free software; you can redistribute it and/or
 ;;; modify it under the terms of the GNU Lesser General Public
@@ -23,6 +23,7 @@
   #:use-module (system base compile)
   #:use-module (system base language)
   #:use-module (system vm vm)
+  #:use-module (ice-9 control)
   #:export (<repl> make-repl repl-vm repl-language repl-options
             repl-tm-stats repl-gc-stats
             repl-welcome repl-prompt repl-read repl-compile repl-eval
@@ -80,8 +81,9 @@
     (if (and eval
              (or (null? (language-compilers (repl-language repl)))
                  (assq-ref (repl-options repl) 'interp)))
-        (eval form (current-module))
-        (vm-load (repl-vm repl) (repl-compile repl form '())))))
+        (% (eval form (current-module)))
+        (let ((compiled (repl-compile repl form '())))
+          (% (vm-load (repl-vm repl) compiled))))))
 
 (define (repl-print repl val)
   (if (not (eq? val *unspecified*))