Prepare 0.8.0-a.3v0.8.0-a.3

* Merge branch 'devel'.

22 files changed, 671 insertions, 136 deletions

diff --git a/INSTALL b/INSTALL
index 68545b7..bb19657 100644
--- a/INSTALL
+++ b/INSTALL
@@ -39,8 +39,8 @@ GNU G-Golf needs the following software to run:
 
 G-Golf release are [[http://ftp.gnu.org/gnu/g-golf/][here]].  The latest tarballs are:
 
-	g-golf-0.8.0-a.2.tar.gz
-	g-golf-0.8.0-a.2.tar.gz.sig
+	g-golf-0.8.0-a.3.tar.gz
+	g-golf-0.8.0-a.3.tar.gz.sig
 
 	[ GPG Key: A3057AD7
 	[ gpg --keyserver keys.gnupg.net --recv-keys A3057AD7
@@ -49,8 +49,8 @@ Assuming you have satisfied the dependencies, open a terminal and
 proceed with the following steps:
 
 	cd <download-path>
-	tar zxf g-golf-0.8.0-a.2.tar.gz
-	cd g-golf-0.8.0-a.2
+	tar zxf g-golf-0.8.0-a.3.tar.gz
+	cd g-golf-0.8.0-a.3
 	./configure [--prefix=/your/prefix] [--with-guile-site=yes]
 	make
 	make install
diff --git a/NEWS b/NEWS
index bfb6059..b383d41 100644
--- a/NEWS
+++ b/NEWS
@@ -26,6 +26,77 @@ warranty.
 
 * Latest News
 
+** February 2023
+
+[[http://www.gnu.org/software/g-golf][GNU G-Golf]] version 0.8.0-a.3 is released.
+
+This is the third release of the upcoming 0.8.0 release, now available
+for testing.
+
+*** Changes since 0.8.0-a.2
+
+Here is a summary of the noteworthy changes since version 0.8.0-a.2. See
+G-Golf [[http://git.savannah.gnu.org/cgit/g-golf.git][git summary]] and [[http://git.savannah.gnu.org/cgit/g-golf.git/log/][git log]] for a complete list and description.
+
+**** Enhancement
+
+Skip Array Length Argument(s)
+
+This release implements skip array-length argument mechanism. This
+affects all functions and methods of any upstream (type)lib that accept
+one or more array argument(s), for which the function or method also
+expect an array length argument.
+
+Starting with this release, users don't have to pass those array length
+arg(s) (more accurately, users may not pass those arg(s) anymore), as
+G-Golf will supply those automatically. Note that this is also valid for
+arrays of uint8 - those arg(s) are 'array of chars', that users must
+provide as a string (as opposed to a list) - for example, see the
+peg-solitaire example, updated accordingly, so that the
+gtk-css-provider-load-from-data call does no longer provide the 'data'
+array length argument.
+
+**** Examples
+
+All
+
+Updated, wrt the above enhancement, to call the g-application-run method
+'without' the args length argument.
+
+Peg Solitaire
+
+In addition, updating the call to gtk-css-provider-load-from-data,
+removing the 'data' array length argument.
+
+**** Bug fixing
+
+Callback and VFunc
+
+In G-Golf, both Callback and VFunc use one (identical) marshal
+procedure, g-golf-callback-closure-marshal, entirely written in scheme,
+which implements, in short, the foreign function interface (ffi) arg
+retrieval and transfornmation into their scheme representation, then
+call the callback of vfunc (user provided) scheme code, then sets the GI
+argument to the return value (if any).
+
+To obtain the ffi arg scheme representation values, G-Golf was calling
+gi-type-info-extract-ffi-return-value (a GI function, in the girffi
+module, not a G-Golf procedure) - but that function has some bug.
+
+G-Golf has now been updated so g-golf-callback-closure-marshal calls a
+'self made' ffi-args->scm (see commit 6a30a12dd) for further details on
+this).
+
+Peg Solitaire
+
+The peg-solitaire example has been updated, as the Callback and VFunc
+bug fixed its snapshot-vfunc method. More specifically its width and
+height argument values are now correct, we no longer need to explicitly
+call get-intrinsic-width and get-intrinsic-height.
+
+
+* Older News
+
 ** January 2023
 
 [[http://www.gnu.org/software/g-golf][GNU G-Golf]] version 0.8.0-a.2 is released.
@@ -86,6 +157,4 @@ GObject.TypeInstance
 GObject.TypeInstance fundamental class support fix. They must inherit
 <gtype-instance> and specify <gtype-class> as their metaclass.
 
-* Older News
-
-For older News, see [[http://www.gnu.org/software/g-golf/news.html][here]].
+** For older News, see [[http://www.gnu.org/software/g-golf/news.html][here]].
diff --git a/README b/README
index 48e4474..4c32efa 100644
--- a/README
+++ b/README
@@ -81,9 +81,9 @@ points to its source code, in the G-Golf sources [[http://git.savannah.gnu.org/c
 
 ** Latest News
 
-January 2023
+February 2023
 
-GNU G-Golf version 0.8.0-a.2 is released.
+GNU G-Golf version 0.8.0-a.3 is released.
 
 Visit the NEWS file or see the [[http://git.savannah.gnu.org/cgit/g-golf.git/tree/NEWS][News]] page for the list of visible changes
 since the last release, as well as older news.
diff --git a/configure.ac b/configure.ac
index 6887c75..65a049a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -31,7 +31,7 @@ AC_PREREQ(2.69)
 
 AC_INIT(
   [g-golf],
-  [0.8.0-a.2],
+  [0.8.0-a.3],
   [bug-g-golf@gnu.org])
 
 AC_CONFIG_AUX_DIR([build-aux])
diff --git a/examples/gtk-4/clipboard.scm b/examples/gtk-4/clipboard.scm
index 9318cc8..614fd15 100755
--- a/examples/gtk-4/clipboard.scm
+++ b/examples/gtk-4/clipboard.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -161,5 +161,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/css-basics.scm b/examples/gtk-4/css-basics.scm
index d20acfc..a53d976 100755
--- a/examples/gtk-4/css-basics.scm
+++ b/examples/gtk-4/css-basics.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -96,5 +96,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/drawing-widget.scm b/examples/gtk-4/drawing-widget.scm
index e9610fd..015c727 100755
--- a/examples/gtk-4/drawing-widget.scm
+++ b/examples/gtk-4/drawing-widget.scm
@@ -87,5 +87,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/hello-world.scm b/examples/gtk-4/hello-world.scm
index 7b5735c..70b5c55 100755
--- a/examples/gtk-4/hello-world.scm
+++ b/examples/gtk-4/hello-world.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -82,5 +82,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/peg-solitaire.scm b/examples/gtk-4/peg-solitaire.scm
index 6c4c30e..c5943c2 100755
--- a/examples/gtk-4/peg-solitaire.scm
+++ b/examples/gtk-4/peg-solitaire.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -73,22 +73,13 @@ exec guile -e main -s "$0" "$@"
 (define-vfunc (get-intrinsic-height-vfunc (self <solitaire-peg>))
   32)
 
-;; For some unknown reason(s) still, the snapshot vfunc is not called with the
-;; the intrinsic width and height values. However both the get-intrinsic-width
-;; and get-intrinsic-height methods work fine, they call their corresponding
-;; vfunc, that we override here above. Till I find out why, let's call those
-;; method explicitly and temporarily comment the width height args.
-
 (define-vfunc (snapshot-vfunc (self <solitaire-peg>) snapshot width height)
   (receive (outline outline:bounds)
       (allocate-c-struct gsk-rounded-rect bounds)
     (gsk-rounded-rect-init-from-rect outline
                                      (graphene-rect-init (graphene-rect-alloc)
-                                                         0 0
-                                                         ;; width height
-                                                         (get-intrinsic-width self)
-                                                         (get-intrinsic-height self))
-                                       3.5) ;; px - approx. 0.3em [default fontsize]
+                                                         0 0  width height)
+                                     3.5) ;; px - approx. 0.3em [default fontsize]
       (push-rounded-clip snapshot outline)
       (append-color snapshot
                     '(0.61 0.1 0.47 1.0) ;; vocaloid
@@ -270,7 +261,7 @@ exec guile -e main -s "$0" "$@"
                  #:row-spacing 6
                  #:row-homogeneous #t))
          (css-provider (let ((provider (make <gtk-css-provider>)))
-                         (gtk-css-provider-load-from-data provider %css-data -1)
+                         (gtk-css-provider-load-from-data provider %css-data)
                          provider)))
     (set-child window grid)
     (do ((i 0
@@ -331,5 +322,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/revealer.scm b/examples/gtk-4/revealer.scm
index 84c0928..7a12ed8 100755
--- a/examples/gtk-4/revealer.scm
+++ b/examples/gtk-4/revealer.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -99,5 +99,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/examples/gtk-4/search-bar.scm b/examples/gtk-4/search-bar.scm
index b758feb..1d746c0 100755
--- a/examples/gtk-4/search-bar.scm
+++ b/examples/gtk-4/search-bar.scm
@@ -5,7 +5,7 @@ exec guile -e main -s "$0" "$@"
 
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -108,5 +108,5 @@ exec guile -e main -s "$0" "$@"
   (let ((app (make <gtk-application>
                #:application-id "org.gtk.example")))
     (connect app 'activate activate)
-    (let ((status (g-application-run app (length args) args)))
+    (let ((status (g-application-run app args)))
       (exit status))))
diff --git a/g-golf/hl-api/argument.scm b/g-golf/hl-api/argument.scm
index 84c7b2c..8faeb6a 100644
--- a/g-golf/hl-api/argument.scm
+++ b/g-golf/hl-api/argument.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -67,6 +67,8 @@
           !scope
           !type-tag
           !type-desc
+          !is-enum?
+          !al-arg?
           !array-type-desc
           !forced-type
           !string-pointer
@@ -101,6 +103,8 @@
   (scope #:accessor !scope)
   (type-tag #:accessor !type-tag #:init-keyword #:type-tag)
   (type-desc #:accessor !type-desc #:init-keyword #:type-desc)
+  (is-enum? #:accessor !is-enum? #:init-keyword #:is-enum?)
+  (al-arg? #:accessor !al-arg? #:init-value #f)
   (array-type-desc #:accessor !array-type-desc)
   (forced-type #:accessor !forced-type #:init-keyword #:forced-type)
   (string-pointer #:accessor !string-pointer)
@@ -160,6 +164,11 @@
                        'scope scope
                        'type-tag type-tag
                        'type-desc type-desc
+                       'is-enum? (and (eq? type-tag 'interface)
+                                      (match type-desc
+                                        ((type name gi-type g-type confirmed?)
+                                         (or (eq? type 'enum)
+                                             (eq? type 'flags)))))
                        'array-type-desc array-type-desc
                        'forced-type forced-type
                        'is-pointer? is-pointer?
diff --git a/g-golf/hl-api/callable.scm b/g-golf/hl-api/callable.scm
index 8d84a6f..d004877 100644
--- a/g-golf/hl-api/callable.scm
+++ b/g-golf/hl-api/callable.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2022 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -81,6 +81,11 @@
                   'caller-owns (g-callable-info-get-caller-owns info)
                   'return-type return-type
                   'type-desc type-desc
+                  'is-enum? (and (eq? return-type 'interface)
+                                      (match type-desc
+                                        ((type name gi-type g-type confirmed?)
+                                         (or (eq? type 'enum)
+                                             (eq? type 'flags)))))
                   'array-type-desc array-type-desc
                   'may-return-null? (g-callable-info-may-return-null info))
       (initialize-callable-arguments self))))
@@ -107,7 +112,7 @@
 
 (define (initialize-callable-arguments callable)
   (let* ((info (!info callable))
-         (override? (!override? callable)) 
+         (override? (!override? callable))
          (is-method? (!is-method? callable))
          (n-arg (g-callable-info-get-n-args info))
          (args (if is-method?
@@ -115,6 +120,7 @@
                    '())))
     (let loop ((i 0)
                (arg-pos (length args))
+               (al-pos '())
                (arguments args)
                (n-gi-arg-in (length args))
                (args-in args)
@@ -122,41 +128,15 @@
                (n-gi-arg-out 0)
                (args-out '()))
       (if (= i n-arg)
-          (let* ((arguments (reverse arguments))
-                 (args-in (reverse args-in))
-                 (args-out (reverse args-out))
-                 (gi-args-in-bv (if (> n-gi-arg-in 0)
-                                    (make-bytevector (* %gi-argument-size
-                                                        n-gi-arg-in)
-                                                     0)
-                                    #f))
-                 (gi-args-in (if gi-args-in-bv
-                                 (bytevector->pointer gi-args-in-bv)
-                                 %null-pointer))
-                 (gi-args-out-bv (if (> n-gi-arg-out 0)
-                                     (make-bytevector (* %gi-argument-size
-                                                         n-gi-arg-out)
-                                                      0)
-                                     #f))
-                 (gi-args-out (if gi-args-out-bv
-                                  (bytevector->pointer gi-args-out-bv)
-                                  %null-pointer)))
-            (when gi-args-in-bv
-              (finalize-callable-arguments args-in gi-args-in-bv !gi-argument-in))
-            (when gi-args-out-bv
-              (finalize-callable-arguments args-out gi-args-out-bv !gi-argument-out))
-            (mslot-set! callable
-                        'n-arg (if is-method? (+ n-arg 1) n-arg)
-                        'arguments arguments
-                        'n-gi-arg-in n-gi-arg-in
-                        'args-in args-in
-                        'gi-args-in gi-args-in
-                        'gi-args-in-bv gi-args-in-bv
-                        'n-gi-arg-out n-gi-arg-out
-                        'args-out args-out
-                        'gi-args-out gi-args-out
-                        'gi-args-out-bv gi-args-out-bv
-                        'gi-arg-result (make-gi-argument)))
+          (initialize-callable-arguments-final-steps callable
+                                                     is-method?
+                                                     n-arg
+                                                     (reverse al-pos)
+                                                     (reverse arguments)
+                                                     (reverse args-in)
+                                                     (reverse args-out)
+                                                     n-gi-arg-in
+                                                     n-gi-arg-out)
           (let* ((arg-info (g-callable-info-get-arg info i))
                  (argument (make <argument> #:info arg-info)))
             (case (!direction argument)
@@ -168,6 +148,7 @@
                            'gi-argument-in-bv-pos n-gi-arg-in)
                (loop (+ i 1)
                      (+ arg-pos 1)
+                     (al-pos-check argument al-pos is-method?)
                      (cons argument arguments)
                      (+ n-gi-arg-in 1)
                      (cons argument args-in)
@@ -183,6 +164,7 @@
                            'gi-argument-out-bv-pos n-gi-arg-out)
                (loop (+ i 1)
                      (+ arg-pos 1)
+                     al-pos
                      (cons argument arguments)
                      (+ n-gi-arg-in 1)
                      (cons argument args-in)
@@ -195,6 +177,7 @@
                            'gi-argument-out-bv-pos n-gi-arg-out)
                (loop (+ i 1)
                      (+ arg-pos 1)
+                     al-pos
                      (cons argument arguments)
                      n-gi-arg-in
                      args-in
@@ -202,6 +185,86 @@
                      (+ n-gi-arg-out 1)
                      (cons argument args-out)))))))))
 
+(define (al-pos-check argument al-pos is-method?)
+  (case (!type-tag argument)
+    ((array)
+     (match (!type-desc argument)
+       ((array fixed-size is-zero-terminated param-n param-tag)
+        (if (= param-n -1)
+            al-pos
+            (let* ((arg-pos (!arg-pos argument))
+                   (param-n (if is-method? (+ param-n 1) param-n))
+                   (u-args-ar-pos (if (< param-n arg-pos) ;; [1]
+                                      (- arg-pos
+                                         (+ (length al-pos) 1))
+                                      (- arg-pos (length al-pos)))))
+              (cons (list u-args-ar-pos
+                          arg-pos ;; 'real' array pos [2]
+                          param-n)
+                    al-pos))))))
+      (else
+       al-pos)))
+
+;; [1]
+
+;; u-arg-ar-pos are 'shifted' to the left - compared to their 'real'
+;; cble-args-ar-pos - by an amount that depens on both previous al args,
+;; and whether the one being processed has its al-pos, param-n,
+;; preceeding or following the array pos itself.
+
+;; [2]
+
+;; the 'real' array pos is the offset of the array arg in the (complete)
+;; cble-args list - we need it to construct the cble-args list
+
+(define (initialize-callable-arguments-final-steps callable
+                                                   is-method?
+                                                   n-arg	;; callable-info-n-args
+                                                   al-pos
+                                                   arguments
+                                                   args-in
+                                                   args-out
+                                                   n-gi-arg-in
+                                                   n-gi-arg-out)
+  (let* ((gi-args-in-bv (if (> n-gi-arg-in 0)
+                            (make-bytevector (* %gi-argument-size
+                                                n-gi-arg-in)
+                                             0)
+                            #f))
+         (gi-args-in (if gi-args-in-bv
+                         (bytevector->pointer gi-args-in-bv)
+                         %null-pointer))
+         (gi-args-out-bv (if (> n-gi-arg-out 0)
+                             (make-bytevector (* %gi-argument-size
+                                                 n-gi-arg-out)
+                                              0)
+                             #f))
+         (gi-args-out (if gi-args-out-bv
+                          (bytevector->pointer gi-args-out-bv)
+                          %null-pointer)))
+    (when gi-args-in-bv
+      (finalize-callable-arguments args-in gi-args-in-bv !gi-argument-in))
+    (when gi-args-out-bv
+      (finalize-callable-arguments args-out gi-args-out-bv !gi-argument-out))
+    (for-each (lambda (item)
+                (match item
+                  ((u-pos c-pos l-pos)
+                   (set! (!al-arg? (list-ref arguments l-pos)) #t))))
+        al-pos)
+    (mslot-set! callable
+                'n-arg (if is-method? (+ n-arg 1) n-arg)
+                'al-pos al-pos
+                'arguments arguments
+                'n-gi-arg-in n-gi-arg-in
+                'args-in args-in
+                'gi-args-in gi-args-in
+                'gi-args-in-bv gi-args-in-bv
+                'n-gi-arg-out n-gi-arg-out
+                'args-out args-out
+                'gi-args-out gi-args-out
+                'gi-args-out-bv gi-args-out-bv
+                'gi-arg-result (make-gi-argument))))
+
 (define (finalize-callable-arguments args gi-args-bv gi-argument-acc)
   (let loop ((args args)
              (i 0))
@@ -215,17 +278,74 @@
              (+ i 1))))))
 
 (define (callable-prepare-gi-arguments callable args)
-  (let ((args-length (length args))
-        (n-arg (!n-arg callable))
-        (n-arg-in (!n-gi-arg-in callable))
-        (override? (!override? callable)))
+  (let* ((args-length (length args))
+         (n-arg (!n-arg callable))
+         (n-arg-in (!n-gi-arg-in callable))
+         (al-pos (!al-pos callable))
+         (effective-n-arg-in (- n-arg-in (length al-pos)))
+         (override? (!override? callable)))
     (if (or (and override?
                  (= args-length n-arg))
-            (= args-length n-arg-in))
-        (begin
+            (= args-length effective-n-arg-in))
+        (let ((args (if (null? al-pos)
+                        args
+                        (u-args->cble-args n-arg-in args al-pos))))
           (callable-prepare-gi-args-in callable args)
           (callable-prepare-gi-args-out callable args args-length n-arg))
-        (error "Wrong number of arguments: " args))))
+        (scm-error 'wrong-arg-nb #f "Wrong number of arguments: ~A ~S"
+                   (list (!name callable) args) #f))))
+
+#!
+
+;; example - to play with
+
+(define cble-args
+  '(e0 3 (ar1-0 ar1-1 ar1-2) e3 (ar2-0) 1 e6 2 (ar3-0 ar3-1)))
+
+(define u-args
+  '(e0 (ar1-0 ar1-1 ar1-2) e3 (ar2-0) e6 (ar3-0 ar3-1)))
+
+(define al-pos
+  '((1 2 1)	;; [1]
+    (3 4 5)
+    (5 8 7)))
+
+;; [1]
+
+;; 0.	u-args ar-pos
+;; 1.	cble-arg ar-pos
+;; 2.	cble-arg al-pos
+
+!#
+
+(define (u-args->cble-args n-arg-in u-args al-pos)
+  (let loop ((i 0)
+             (args u-args)
+             (al-pos al-pos)
+             (cble-args '()))
+    (if (= i n-arg-in)
+        (reverse! cble-args)
+        (if (null? al-pos)
+            (loop (+ i 1)
+                  (cdr args)
+                  '()
+                  (cons (car args) cble-args))
+            (match (car al-pos)
+              ((u-pos c-pos l-pos)
+               (if (= i l-pos)
+                   (let ((ar (list-ref u-args u-pos)))
+                     (loop (+ i 1)
+                           args
+                           (cdr al-pos)
+                           (cons (cond ((list? ar) (length ar))
+                                       ((string? ar) -1)
+                                       (else
+                                        (error "What array is this " ar)))
+                                 cble-args)))
+                   (loop (+ i 1)
+                         (cdr args)
+                         al-pos
+                         (cons (car args) cble-args)))))))))
 
 (define %allow-none-exceptions
   '(child-setup-data-destroy))
@@ -332,11 +452,12 @@
                (error "Invalid array argument: " value))
            (match type-desc
              ((array fixed-size is-zero-terminated param-n param-tag)
-              (let* ((param-n (case param-n
-                                ((-1) param-n)
-                                (else
-                                 (if is-method? (+ param-n 1) param-n))))
-                     (arg-n (list-ref args param-n)))
+              (let* ((param-n (if (= param-n -1)
+                                  -1
+                                  (if is-method? (+ param-n 1) param-n)))
+                     (arg-n (if (= param-n -1)
+                                -1
+                                (list-ref args param-n))))
                 (case param-tag
                   ((utf8
                     filename)
@@ -368,6 +489,20 @@
                           (gi-argument-set! gi-argument 'v-pointer value))
                          (else
                           (error "Invalid (uint8 array) argument: " value))))
+                  ((interface)
+                   (match (!array-type-desc clb/arg)
+                     ((type name gi-type g-type confirmed?)
+                      (case type
+                        ((object)
+                         (let ((ptrs (map !g-inst value)))
+                           (gi-argument-set! gi-argument 'v-pointer
+                                             (if (or is-zero-terminated
+                                                     (= arg-n -1))
+                                                 (scm->gi-pointers ptrs)
+                                                 (scm->gi-n-pointer ptrs arg-n)))))
+                        (else
+                         (warning "Unimplemented (prepare args-in) type - array;"
+                                  (format #f "~S" type-desc)))))))
                   (else
                    (warning "Unimplemented (prepare args-in) type - array;"
                             (format #f "~S" type-desc)))))))))
@@ -792,6 +927,7 @@
         #:direction 'in
         #:type-tag 'interface
         #:type-desc (list type r-name gi-type id confirmed?)
+        #:is-enum? #f
         #:forced-type 'pointer
         #:is-pointer? #t
         #:may-be-null? #f
diff --git a/g-golf/hl-api/callback.scm b/g-golf/hl-api/callback.scm
index 5ecc1d6..214017a 100644
--- a/g-golf/hl-api/callback.scm
+++ b/g-golf/hl-api/callback.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2019 - 2022
+;;;; Copyright (C) 2019 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -27,6 +27,7 @@
 
 
 (define-module (g-golf hl-api callback)
+  #:use-module (system foreign)
   #:use-module (ice-9 threads)
   #:use-module (ice-9 match)
   #:use-module (ice-9 receive)
@@ -109,24 +110,35 @@
     (mslot-set! self
                 'ffi-cif (callback-ffi-cif self))))
 
+(define (ffi-prep-cif-elements callback)
+  (let* ((ffi-cif-bv (make-bytevector (ffi-cif-size) 0))
+         (r-type-info (g-callable-info-get-return-type (!info callback)))
+         (r-type (g-type-info-get-ffi-type r-type-info))
+         (n-arg (!n-arg callback))
+         (a-types-bv (make-bytevector (* n-arg (ffi-type-size)) 0)))
+    (g-base-info-unref r-type-info)
+    (values (bytevector->pointer ffi-cif-bv)
+            n-arg
+            r-type
+            (bytevector->pointer a-types-bv))))
+
 (define (callback-ffi-cif callback)
-  (let ((n-arg (!n-arg callback)))
-    (case n-arg
-      ((0) %null-pointer)
-      (else
-       (let ((ffi-cif
-              (bytevector->pointer
-               (make-bytevector (* n-arg (ffi-type-size)) 0))))
-         (let loop ((arguments (!arguments callback))
-                    (w-ptr ffi-cif))
-           (match arguments
-             (() ffi-cif)
-             ((argument . rest)
-              (bv-ptr-set! w-ptr
-                           (gi-type-tag-get-ffi-type (!type-tag argument)
-                                                     (!is-pointer? argument)))
-              (loop rest
-                    (gi-pointer-inc w-ptr))))))))))
+  (receive (ffi-cif n-arg r-type a-types)
+      (ffi-prep-cif-elements callback)
+    (if (= n-arg 0)
+        %null-pointer
+        (let loop ((arguments (!arguments callback))
+                   (w-ptr a-types))
+          (match arguments
+            (()
+             (ffi-prep-cif ffi-cif n-arg r-type a-types)
+             ffi-cif)
+            ((argument . rest)
+             (bv-ptr-set! w-ptr
+                          (gi-type-tag-get-ffi-type (!type-tag argument)
+                                                    (!is-pointer? argument)))
+             (loop rest
+                   (gi-pointer-inc w-ptr))))))))
 
 (define (g-callable-info-make-closure info
                                       ffi-cif
@@ -181,23 +193,60 @@
                                    #:is-method? (!is-method? callback)
                                    #:forced-type return-type))))))
         ((argument . rests)
-         (let ((type-info (!type-info argument)))
-           (if type-info
-               (gi-type-info-extract-ffi-return-value type-info ffi-arg gi-argument)
-               ;; a 'manually built' instance argument, the first argument of
-               ;; a method.
-               (gi-type-tag-extract-ffi-return-value 'interface
-                                                     'object
-                                                     ffi-arg
-                                                     gi-argument))
+         (let* ((type-tag (!type-tag argument))
+                (type-desc (!type-desc argument))
+                (is-pointer? (!is-pointer? argument))
+                (is-enum? (!is-enum? argument))
+                (gi-argument (or (!gi-argument-in argument)
+                                 (!gi-argument-out argument)))
+                (forced-type (!forced-type argument))
+                (ffi-value (ffi-arg->scm ffi-arg type-tag is-pointer? is-enum?)))
            (loop rests
                  (gi-pointer-inc ffi-arg)
-                 (cons (%gi-argument->scm (!type-tag argument)
-                                          (!type-desc argument)
-                                          gi-argument
-                                          argument
-                                          #:forced-type (!forced-type argument)
-                                          #:is-pointer? (!is-pointer? argument))
+                 (cons (case type-tag
+                         ((boolean
+                           int8
+                           uint8
+                           int16
+                           uint16
+                           int32
+                           uint3
+                           unichar
+                           int64
+                           uint64
+                           float
+                           double
+                           gtype
+                           utf
+                           filename)
+                          ffi-value)
+                         ((array
+                           glist
+                           gslist
+                           ghash
+                           error)
+                          (begin
+                            (gi-argument-set! gi-argument 'v-pointer ffi-value)
+                            (%gi-argument->scm type-tag
+                                               type-desc
+                                               gi-argument
+                                               argument
+                                               #:forced-type forced-type
+                                               #:is-pointer? is-pointer?)))
+                         ((interface)
+                          (if is-enum?
+                              (gi-argument-set! gi-argument 'v-int32 ffi-value)
+                              (gi-argument-set! gi-argument 'v-pointer ffi-value))
+                          (%gi-argument->scm type-tag
+                                             type-desc
+                                             gi-argument
+                                             argument
+                                             #:forced-type forced-type
+                                             #:is-pointer? is-pointer?))
+                         ((void)
+                          (if is-pointer?
+                              ffi-value
+                              (error "unlikely possible"))))
                        args))))))))
 
 (define %g-golf-callback-closure-marshal
diff --git a/g-golf/hl-api/ccc.scm b/g-golf/hl-api/ccc.scm
index 572545a..18b1e62 100644
--- a/g-golf/hl-api/ccc.scm
+++ b/g-golf/hl-api/ccc.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -57,9 +57,11 @@
           !override?
           !is-method?
           !n-arg
+          !al-pos
           !caller-owns
           !return-type
           !type-desc
+          !is-enum?
           !array-type-desc
           !string-pointer
           !bv-cache
@@ -94,9 +96,11 @@
   (override? #:accessor !override? #:init-keyword #:override? #:init-value #f)
   (is-method? #:accessor !is-method?)
   (n-arg #:accessor !n-arg)
+  (al-pos #:accessor !al-pos)
   (caller-owns #:accessor !caller-owns)
   (return-type #:accessor !return-type)
   (type-desc #:accessor !type-desc)
+  (is-enum? #:accessor !is-enum?)
   (array-type-desc #:accessor !array-type-desc)
   (string-pointer #:accessor !string-pointer)
   (bv-cache #:accessor !bv-cache #:init-value #f)
diff --git a/g-golf/hl-api/function.scm b/g-golf/hl-api/function.scm
index cb721a4..cda2f27 100644
--- a/g-golf/hl-api/function.scm
+++ b/g-golf/hl-api/function.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2019 - 2022
+;;;; Copyright (C) 2019 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -218,7 +218,9 @@
                         (case (!direction argument)
                           ((in
                             inout)
-                           argument)
+                           (if (!al-arg? argument)
+                               #f
+                               argument))
                           (else
                            #f)))
               arguments)))))
diff --git a/g-golf/override/gtk.scm b/g-golf/override/gtk.scm
index 37cb905..46437da 100644
--- a/g-golf/override/gtk.scm
+++ b/g-golf/override/gtk.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2020 - 2022
+;;;; Copyright (C) 2020 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -29,7 +29,7 @@
 (define-module (g-golf override gtk)
   #:export (gtk-container-child-get-property-ov
             gtk-container-child-set-property-ov
-            gtk-list-store-new-ov
+            #;gtk-list-store-new-ov
             gtk-list-store-set-value-ov
             gtk-tree-store-set-value-ov
             gtk-tree-model-get-value-ov
@@ -83,7 +83,7 @@
             (error "No child property" container name))))
    '(0 1 2 3)))
 
-(define (gtk-list-store-new-ov proc)
+#;(define (gtk-list-store-new-ov proc)
   (values
    #f
    `(lambda (g-types)
diff --git a/g-golf/override/override.scm b/g-golf/override/override.scm
index 73ee71b..9862280 100644
--- a/g-golf/override/override.scm
+++ b/g-golf/override/override.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2020 - 2022
+;;;; Copyright (C) 2020 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -39,7 +39,7 @@
 
     "gtk_container_child_get_property"
     "gtk_container_child_set_property"
-    "gtk_list_store_newv"
+    #;"gtk_list_store_newv"
     "gtk_list_store_set_value"
     "gtk_tree_store_set_value"
     "gtk_tree_model_get_value"
diff --git a/g-golf/support/ffi.scm b/g-golf/support/ffi.scm
index 63ca479..b51abdf 100644
--- a/g-golf/support/ffi.scm
+++ b/g-golf/support/ffi.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2022
+;;;; Copyright (C) 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -27,13 +27,213 @@
 
 
 (define-module (g-golf support ffi)
+  #:use-module (ice-9 match)
+  #:use-module (system foreign)
+  #:use-module (srfi srfi-4)
   #:use-module (g-golf support libg-golf)
+  #:use-module (g-golf gi utils)
+  #:use-module (g-golf support utils)
 
-  #:export (ffi-type-size))
+  #:export (ffi-args->scm
+            ffi-arg->scm
+            ffi-arg-boolean->scm
+            ffi-arg-int8->scm
+            ffi-arg-uint8->scm
+            ffi-arg-int16->scm
+            ffi-arg-uint16->scm
+            ffi-arg-int16->scm
+            ffi-arg-uint16->scm
+            ffi-arg-int32->scm
+            ffi-arg-uint32->scm
+            ffi-arg-int64->scm
+            ffi-arg-uint64->scm
+            ffi-arg-float->scm
+            ffi-arg-double->scm
+            ffi-arg-gtype->scm
+            ffi-arg-string->scm
+            ffi-arg-pointer->scm
+
+            ffi-cif-size
+            ffi-type-size
+            ffi-prep-cif
+            #;ffi-pack-double))
+
+
+(define (ffi-args->scm ffi-args type-descs)
+  (let loop ((ffi-arg ffi-args)
+             (descs type-descs)
+             (results '()))
+    (match descs
+      (()
+       (reverse! results))
+      ((desc . rest)
+       (loop (gi-pointer-inc ffi-arg)
+             rest
+             (cons (match desc
+                     ((type-tag is-póinter? is-enum?)
+                      (ffi-arg->scm ffi-arg type-tag is-póinter? is-enum?)))
+                   results))))))
+
+(define (ffi-arg->scm ffi-arg type-tag is-pointer? is-enum?)
+  (case type-tag
+    ((boolean)
+     (ffi-arg-boolean->scm ffi-arg))
+    ((int8)
+     (ffi-arg-int8->scm ffi-arg))
+    ((uint8)
+     (ffi-arg-uint8->scm ffi-arg))
+    ((int16)
+     (ffi-arg-int16->scm ffi-arg))
+    ((uint16)
+     (ffi-arg-uint16->scm ffi-arg))
+    ((int32)
+     (ffi-arg-int32->scm ffi-arg))
+    ((uint32
+      unichar)
+     (ffi-arg-uint32->scm ffi-arg))
+    ((int64)
+     (ffi-arg-int64->scm ffi-arg))
+    ((uint64)
+     (ffi-arg-uint64->scm ffi-arg))
+    ((float)
+     (ffi-arg-float->scm ffi-arg))
+    ((double)
+     (ffi-arg-double->scm ffi-arg))
+    ((gtype)
+     (ffi-arg-gtype->scm ffi-arg))
+    ((utf8
+      filename)
+     (ffi-arg-string->scm ffi-arg))
+    ((array
+      glist
+      gslist
+      ghash
+      error)
+     (ffi-arg-pointer->scm ffi-arg))
+    ((interface)
+     ;; Needs to handle enums specially:
+     ;; https://bugzilla.gnome.org/show_bug.cgi?id=665150
+     (if is-enum?
+         (ffi-arg-int32->scm ffi-arg)
+         (ffi-arg-pointer->scm ffi-arg)))
+    ((void)
+     (if is-pointer?
+         (ffi-arg-pointer->scm ffi-arg)
+         'void))
+    (else
+     (scm-error 'failed #f
+                "Unimplemented ffi-arg->scm type-tag: ~A"
+                (list type-tag) #f))))
+
+(define (ffi-arg-boolean->scm ffi-arg)
+  (let* ((size (sizeof unsigned-int))
+         (bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr size)))
+    (gi->scm (case size
+               ((4)
+                (u32vector-ref bv 0))
+               ((8)
+                (u64vector-ref bv 0))
+               (else
+                (error "what machine is this?")))
+             'boolean)))
+
+(define (ffi-arg-int8->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof int8))))
+    (s8vector-ref bv 0)))
+
+(define (ffi-arg-uint8->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof uint8))))
+    (u8vector-ref bv 0)))
+
+(define (ffi-arg-int16->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof int16))))
+    (s16vector-ref bv 0)))
+
+(define (ffi-arg-uint16->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof uint16))))
+    (u16vector-ref bv 0)))
+
+(define (ffi-arg-int32->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof int32))))
+    (s32vector-ref bv 0)))
+
+(define (ffi-arg-uint32->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof uint32))))
+    (u32vector-ref bv 0)))
+
+(define (ffi-arg-int64->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof int64))))
+    (s64vector-ref bv 0)))
+
+(define (ffi-arg-uint64->scm ffi-arg)
+  (let* ((bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr (sizeof uint64))))
+    (u64vector-ref bv 0)))
+
+(define (ffi-arg-float->scm ffi-arg)
+  (let* ((size (sizeof float))
+         (bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr size)))
+    (case size
+      ((4)
+       (f32vector-ref bv 0))
+      ((8)
+       (f64vector-ref bv 0))
+      (else
+       (error "what machine is this?")))))
+
+(define (ffi-arg-double->scm ffi-arg)
+  (let* ((size (sizeof double))
+         (bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr size)))
+    (case size
+      ((4)
+       (f32vector-ref bv 0))
+      ((8)
+       (f64vector-ref bv 0))
+      (else
+       (error "what machine is this?")))))
+
+(define (ffi-arg-gtype->scm ffi-arg)
+  (let* ((size (sizeof size_t))
+         (bv-ptr (dereference-pointer ffi-arg))
+         (bv (pointer->bytevector bv-ptr size)))
+    (case size
+      ((4)
+       (u32vector-ref bv 0))
+      ((8)
+       (u64vector-ref bv 0))
+      (else
+       (error "what machine is this?")))))
+
+(define (ffi-arg-string->scm ffi-arg)
+  (gi->scm (dereference-pointer ffi-arg) 'string))
+
+(define (ffi-arg-pointer->scm ffi-arg)
+  (gi->scm (dereference-pointer ffi-arg) 'pointer))
 
 
 ;;;
 ;;; From libg-golf
 ;;;
 
-(define ffi-type-size ffi_type_size)
+(define ffi-cif-size gg_ffi_cif_size)
+
+(define ffi-type-size gg_ffi_type_size)
+
+(define (ffi-prep-cif cif n-args r-type a-types)
+  (let ((ffi-status (gg_ffi_prep_cif cif n-args r-type a-types)))
+    (unless (= ffi-status 0)
+      (scm-error 'failed #f "ffi_prep_cif failed: ~A"
+                 (list ffi-status) #f))))
+
+#;(define (ffi-pack-double ffi-arg)
+  (gg_ffi_pack_double ffi-arg))
diff --git a/g-golf/support/libg-golf.scm b/g-golf/support/libg-golf.scm
index 539d252..0e395bb 100644
--- a/g-golf/support/libg-golf.scm
+++ b/g-golf/support/libg-golf.scm
@@ -1,7 +1,7 @@
 ;; -*- mode: scheme; coding: utf-8 -*-
 
 ;;;;
-;;;; Copyright (C) 2016 - 2022
+;;;; Copyright (C) 2016 - 2023
 ;;;; Free Software Foundation, Inc.
 
 ;;;; This file is part of GNU G-Golf
@@ -31,7 +31,10 @@
   #:use-module (g-golf init)
   
   #:export (;; FFI
-            ffi_type_size
+            gg_ffi_cif_size
+            gg_ffi_type_size
+            gg_ffi_prep_cif
+            gg_ffi_pack_double
 
             ;; Misc.
             pointer_address_size
@@ -67,12 +70,33 @@
 ;;; FFI
 ;;;
 
-(define ffi_type_size
+(define gg_ffi_cif_size
   (pointer->procedure size_t
-                      (dynamic-func "ffi_type_size"
+                      (dynamic-func "gg_ffi_cif_size"
                                     %libg-golf)
                       (list)))
 
+(define gg_ffi_type_size
+  (pointer->procedure size_t
+                      (dynamic-func "gg_ffi_type_size"
+                                    %libg-golf)
+                      (list)))
+
+(define gg_ffi_prep_cif
+  (pointer->procedure int
+                      (dynamic-func "gg_ffi_prep_cif"
+                                    %libg-golf)
+                      (list '*			;; *cif
+                            unsigned-int	;; n-args
+                            '*			;; *return-type
+                            '*)))		;; **arg-types
+
+(define gg_ffi_pack_double
+  (pointer->procedure double
+                      (dynamic-func "gg_ffi_pack_double"
+                                    %libg-golf)
+                      (list '*)))		;; *ffi-arg
+
 
 ;;;
 ;;; Misc.
diff --git a/libg-golf/gg-ffi.c b/libg-golf/gg-ffi.c
index 148b7bd..15666df 100644
--- a/libg-golf/gg-ffi.c
+++ b/libg-golf/gg-ffi.c
@@ -31,6 +31,7 @@
 #include <math.h>
 
 #include <ffi.h>
+#include <ffitarget.h>
 
 
 /*
@@ -39,9 +40,47 @@
 */
 
 size_t
-ffi_type_size ()
+gg_ffi_cif_size ()
+{
+  size_t n = sizeof(ffi_cif);
+
+  return n;
+}
+
+size_t
+gg_ffi_type_size ()
 {
   size_t n = sizeof(ffi_type *);
 
   return n;
 }
+
+int
+gg_ffi_prep_cif (ffi_cif *cif, \
+                 unsigned n_args, \
+                 ffi_type *r_type, \
+                 ffi_type **a_types)
+{
+  int ffi_status;
+
+  /* printf("return type: %d\n", r_type->type);
+   * for (unsigned i = 0; i < n_args; i++) {
+   *   printf ("  arg %d type: %d\n", i, a_types[i]->type);
+   * }
+  */
+
+  ffi_status = ffi_prep_cif (cif, FFI_DEFAULT_ABI, n_args, r_type, a_types);
+
+  return ffi_status;
+}
+
+double
+gg_ffi_pack_double (void **arg)
+{
+  double dble;
+
+  dble =  *(double *) (*arg);
+  /* printf ("  ffi_arg dble: %f\n", dble); */
+
+  return dble;
+}
diff --git a/libg-golf/gg-ffi.h b/libg-golf/gg-ffi.h
index bba8d13..2865456 100644
--- a/libg-golf/gg-ffi.h
+++ b/libg-golf/gg-ffi.h
@@ -1,7 +1,7 @@
 /*  -*- mode: C; coding: utf-8 -*-
 
 ####
-#### Copyright (C) 2022
+#### Copyright (C) 2023
 #### Free Software Foundation, Inc.
 
 #### This file is part of GNU G-Golf.
@@ -39,4 +39,16 @@
 */
 
 size_t
-ffi_type_size ();
+gg_ffi_cif_size ();
+
+size_t
+gg_ffi_type_size ();
+
+int
+gg_ffi_prep_cif (ffi_cif *cif, \
+                 uint n_args, \
+                 ffi_type *r_type, \
+                 ffi_type **a_types);
+
+double
+gg_ffi_pack_double (void **arg);