Small enhancement to options interface

[Neil Jerram]

A strange thing about Guile's options interface is that xxx-options,
xxx-enable and xxx-disable all want a quoted option symbol as their
argument, whereas xxx-set! wants an _unquoted_ symbol.

What is worse, is that if you call xxx-set! with a _quoted_ symbol, as
in (debug-set! 'stack 500), it does nothing, but silently -- there is
no clear indication that what you asked for didn't work.

(It may be arguable that people should expect xxx-set! to take an
unquoted symbol by analogy with set! ...  but personally I've always
found the current behaviour confusing, and I frequently get it wrong.)

The patch below enhances xxx-set! so that it accepts both an unquoted
and a quoted symbol, and also simplifies some of the rather obfuscated
definition of define-option-interface.  With this enhancement, we keep
backwards compatibility, but we can document in future that the
options functions always take a quoted symbol. 

What do you think?

(Further thought - if this enhancement is good, would it be even
better, if optexp is not a symbol, just to let it be evaluated?  This
would make xxx-set! even more similar to xxx-enable and xxx-disable,
as the latter are procedures.)

        Neil

cd /home/neil/Guile/cvs/guile-core/ice-9/
diff -Naur /home/neil/Guile/cvs/guile-core/ice-9/boot-9.scm.old 
/home/neil/Guile/cvs/guile-core/ice-9/boot-9.scm
--- /home/neil/Guile/cvs/guile-core/ice-9/boot-9.scm.old        Tue Oct 29 
00:09:13 2002
+++ /home/neil/Guile/cvs/guile-core/ice-9/boot-9.scm    Tue Oct 29 00:10:01 2002
@@ -2026,24 +2026,32 @@
                         (begin (,interface (append (,interface)
                                                    (list '(,'unquote name)
                                                          (,'unquote exp))))
-                               (,interface)))))))
+                               (,interface))))))
+
+        (get-option-symbol (lambda (optexp)
+                             (cond ((symbol? optexp)
+                                    optexp)
+                                   ((and (list? optexp)
+                                         (= (length optexp) 2)
+                                         (eq? (car optexp) 'quote))
+                                    (cadr optexp))
+                                   (else
+                                    (error "Option must be specified as a 
symbol or quoted symbol"))))))
     (procedure->memoizing-macro
      (lambda (exp env)
-       (cons 'begin
-            (let* ((option-group (cadr exp))
-                   (interface (car option-group)))
-              (append (map (lambda (name constructor)
-                             `(define ,name
-                                ,(constructor interface)))
-                           (cadr option-group)
-                           (list make-options
-                                 make-enable
-                                 make-disable))
-                      (map (lambda (name constructor)
-                             `(defmacro ,name
-                                ,@(constructor interface)))
-                           (caddr option-group)
-                           (list make-set!)))))))))
+       (let* ((option-group (cadr exp))
+             (interface (car option-group))
+             (options/enable/disable (cadr option-group)))
+        `(begin
+           (define ,(car options/enable/disable)
+             ,(make-options interface))
+           (define ,(cadr options/enable/disable)
+             ,(make-enable interface))
+           (define ,(caddr options/enable/disable)
+             ,(make-disable interface))
+           (defmacro ,(caaddr option-group) (opt val)
+             `(,,(car options/enable/disable)
+               (list ',(,get-option-symbol opt) ,val)))))))))
 
 (define-option-interface
   (eval-options-interface

Diff finished at Tue Oct 29 00:10:11