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From: dmg@ssc-vax.uucp (David M Geary)
Newsgroups: comp.lang.misc,comp.object
Subject: Re:  Type Systems and Dynamic Binding
Message-ID: <3843@ssc-bee.ssc-vax.UUCP>
Date: 15 Apr 91 18:21:45 GMT
Sender: news@ssc-vax.UUCP
Organization: Boeing Aerospace & Electronics
Lines: 134
Originator: dmg@ssc-vax

]    Dan Bernstein
]]   David Geary

]]   Dan Bernstein claims to be able to implement dynamic typing on top of C:
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

] Although I can implement and have implemented dynamic typing with a
] suitable preprocessor over C, I did not make that claim in the quoted
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
] material. Please read a quote before you paraphrase it.

]The original example in question was *presented* as an example of what
]people do with heterogeneous (dynamically typed) lists. I responded with
                                                         ^^^^^^^^^^^^^^^^
]the above structure to show how you implement the same thing in C, and
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
]here Geary claims that the example was no longer an example of dynamic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
]typing. Sheesh. My response:
 ^^^^^^

  Sheesh yourself.  Either it *was* an example of dynamic typing or it
was *not*.  You cannot have it both ways, Dan.  I did not claim
that your example was *no longer* an example of dynamic typing.  I said
that your example was *never* an example of dynamic typing.
  Here, BTW, since you do not want me to paraphrase, is the original
article written by Bernstein:

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

%  = Darren New
%% = Dan Bernstein

In article <25655:Mar2803:50:2491@kramden.acf.nyu.edu> (Dan Bernstein) writes:
%In article <49087@nigel.ee.udel.edu> new@ee.udel.edu (Darren New) writes:
%% Am I crazy, or isn't (void *) impossible to indirect?  Don't you have
%% to type-cast it first?  Isn't this dynamic typing implemented on top of
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
%% C?
  ^^^

%YES. People are tossing around the term ``dynamic typing'' as if it were
%some truly important feature. ``Yeah, Bob, not only does the language
%have *loops*, but it has *dynamic typing*!'' ``Wow! *Dynamic typing*?
%Really?''

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

  YES is pretty clear to me.  Did you really mean NO?  If so, then I 
misunderstood.


]If you had been keeping up with the discussion in comp.lang.misc, you
]would understand that giving the same name to variables in different
]structures does NOT imply any magical connection between those
]variables. In order to solve your problem as stated, you must make the
]connection explicit, like so (as per my structure as above):

  Exactly what I was trying to say.  Dan Bernstein is *not* implementing
dynamic typing on top of C.

  Since it appeared to me that Bernstein was claiming to be implementing
dynamic typing on top of C, I posted the following challenge for Dan:

]]Developer A implements buttons, menus, and icons which are displayable in a
]]window.  Developer A provides developer B with:

]]  1)  Header files defining structures for buttons, menus and icons.
]]      (menu.h, button.h and icon.h).

]]  2)  Object modules which implement functionality for each.
]]      (menu.o, button.o and icon.o).

]] Menus, buttons, and icons all have a pointer to a redraw function in their
]] structure definition; however, structures for buttons, menus and icons are
]] all different, ie:

]] struct button                        struct menu
]] {                                    { 
]]   int   x,y,w,h;                       int    x,y,w,h;
]]   char* text;                          int    numItems;
                                        char** itemText; 
]]   void  (*redraw)();                    
]] };                                     void   (*redraw)();                   
                                      };
]] struct icon
]] {
]]   int      x,y,w,h;
]]   bitmap*  picture;

]]   void     (*redraw)();
]] };

]] Developer A provides a function that returns a list of things in a window
]](things being buttons, menus, and icons).  Let's call the function
]]getListOfThingsInWindow().

]] Now, developer B, given the header files and object modules defined above,
]]processes the list, and displays all items on the list in a fashion similar
]]to:

]]   drawWindowThings(window)
]]     window_t* window;
]]   {
]]     list_t*  wlist = getListOfThingsInWindow(window);

]]     for(each object in wlist)
]]       redraw the object
]]   }

]]  Dan, since you can implement dynamic typing in C, would you please post
]]the *appropriate macros* so that developer B can get his job done, without
]]*in any way* having to modify (recompile) the object modules that are supplied
]]from developer A.

Dan replies with:

foo->redraw(foo->object); Done.

  No.  Wrong.  Not done.  Dan is using his own structure instead of those
I provided in the example.  In the example above, each object in wlist
must be a void*.  You cannot defererence a void pointer.  You cannot implement
dynamic typing in C without writing an external preprocessor.  Period.

  BTW, this whole series of postings occurred because I thought that Bernstein
claimed to have implemented dynamic typing in C without writing any
*external* preprocessor.  (As did others in this newsgroup).  Since this is 
impossible to do, I posted the above challenge.  Now, Dan seems to be claiming 
that he never stated he could implement dynamic typing on top of C without 
writing any *external* preprocessor.

  If Bernstein's claim today is that he *cannot* implement dynamic typing
on top of C withoug writing an external preprocessor, then we are in 
agreement.