• Mark Evans (4/4) Feb 19 2003 http://nice.sourceforge.net/visitor.html
• Mark Evans (5/5) Mar 02 2003 This is the type system used in both Needle and Nice.
• Walter (4/7) Mar 07 2003 Do all the incarnations of a particular multimethod function all need to...
• Mark Evans (2/4) Mar 07 2003 What does that mean, 'done at once'?
• Walter (4/7) Mar 07 2003 be
• Mark Evans (37/42) Mar 07 2003 Off the top of my head, no. The (first-class) generic function has some...
• Dan Liebgold (5/5) Mar 10 2003 Correct me if I'm wrong, but aren't multimethod dispatch methods always ...
• Bill Cox (3/9) Mar 10 2003 That sounds right to me.
• Walter (5/10) Mar 10 2003 some
• yuqianzhou yahoo.co.uk (10/15) Mar 11 2003 Great! Walter, sounds like you're interested in implementing multimethod...
• Craig Black (14/14) Mar 24 2003 Hey peoples,
• Mike Wynn (3/12) Mar 24 2003 why not compile the binary tree into a set of cmps and jmps ?
• Craig Black (2/3) Mar 31 2003 Hmmm ..... sounds difficult to implement but a good idea!
• Ilya Minkov (3/6) Apr 09 2003 Why not optimise out all of the cmps and jmps altogether then. ;>
• Craig Black (8/14) Apr 10 2003 There is no way to "optimize out" the logic in the binary tree. It must
• Craig Black (2/2) Mar 31 2003 I was just thinking, you could also use a hash table.

Mark Evans <Mark_member pathlink.com> writes:

http://nice.sourceforge.net/visitor.html

Good advice from the Nice language,
http://nice.sourceforge.net/index.html

Mark

Mark Evans <Mark_member pathlink.com> writes:

This is the type system used in both Needle and Nice.

Mark

"On the integration of functional programming, class-based object-oriented
programming, and multi-methods"

http://www.exalead.com/Francois.Bourdoncle/mlsub.html

"Walter" <walter digitalmars.com> writes:

"Mark Evans" <Mark_member pathlink.com> wrote in message
news:b314qm$sns$1 digitaldaemon.com...
 http://nice.sourceforge.net/visitor.html

 Good advice from the Nice language,
 http://nice.sourceforge.net/index.html

Do all the incarnations of a particular multimethod function all need to be
done at once (like methods in a class, or members of a template)?

Mark Evans <Mark_member pathlink.com> writes:

Do all the incarnations of a particular multimethod function all need to be
done at once (like methods in a class, or members of a template)?

What does that mean, 'done at once'?

Mark

"Walter" <walter digitalmars.com> writes:

"Mark Evans" <Mark_member pathlink.com> wrote in message
news:b4b6sq$2fpg$1 digitaldaemon.com...
Do all the incarnations of a particular multimethod function all need to


be
done at once (like methods in a class, or members of a template)?

 What does that mean, 'done at once'?

All be in the same scope, just like overloaded functions must be.

Mark Evans <Mark_member pathlink.com> writes:

Walter says...
Do all the incarnations of a particular multimethod function all need to
be done at once (like methods in a class, or members of a template)?

 What does that mean, 'done at once'?

All be in the same scope, just like overloaded functions must be.

Off the top of my head, no.  The (first-class) generic function has some scope
but the multimethods it 'owns' may live anywhere.  It's just a question of how
the call is dispatched.  That determination is made by the ("multi") argument
specializers and the design of the dispatch rules in the language.  Those rules
could be as wild as your imagination.

Of course a major benefit of multimethods is that they can (should?) live
outside class scope.  This technique solves exactly Bill's problem of how to
'add members to multiple existing classes.'  In terms of scope they might, e.g.,
live in several different modules, even if none of them are class members per
se.

Always subject to correction,
Mark


Possibly helpful links, and a quote:

http://www.openbg.net/sto/newsread.php?grp=comp.lang.clos&msg=msg00246.html
http://www.openbg.net/sto/newsread.php?grp=comp.lang.clos&msg=msg00244.html
http://www.op59.net/cmm/cmm-0.15/users.html
http://www.functionalobjects.com/resources/white-paper.phtml
http://monday.sourceforge.net/wiki/index.php/MultiMethods
http://www.cyberdyne-object-sys.com/oofaq2/body/basics.htm#S1.19
http://www.psg.com/~dlamkins/sl/chapter14.html
http://www.cis.ohio-state.edu/~gb/Brew/Publications/HalfNHalf.pdf
http://www.research.ibm.com/people/d/dgrove/papers/phd-thesis.pdf
http://www.cs.washington.edu/homes/todd/research/ecoop99.ps

'In object-oriented languages with multimethods...the appropriate method to
invoke for a message send can depend on the run-time class of any subset of the
message arguments, rather than a distinguished receiver argument. Multimethods
unify the otherwise distinct concepts of functions, methods, and static
overloading, leading to a potentially simpler language. They also support safe
covariant overriding in the face of subtype polymorphism, providing a natural
solution to the "binary method" problem and a simple implementation of the
"strategy" design pattern.  Finally, multimethods allow clients to add new
operations that dynamically dispatch on existing classes, supporting a form of
what we call "open objects" ... that enables easy programming of the "visitor"
design pattern and is a key element of aspect-oriented programming. Open objects
also relieve the tension observed by others between ease of adding operations to
existing classes and ease of adding subclasses.'

Dan Liebgold <Dan_member pathlink.com> writes:

Correct me if I'm wrong, but aren't multimethod dispatch methods always some
sort of runtime search at the time of the method call?  Even if the search is
optimized by the compiler (to a binary search or somesuch), doesn't this
implementational requirement cross the line in terms of performance?

Dan

Bill Cox <bill viasic.com> writes:

Dan Liebgold wrote:
 Correct me if I'm wrong, but aren't multimethod dispatch methods always some
 sort of runtime search at the time of the method call?  Even if the search is
 optimized by the compiler (to a binary search or somesuch), doesn't this
 implementational requirement cross the line in terms of performance?
 
 Dan

That sounds right to me.

Bill

"Walter" <walter digitalmars.com> writes:

"Dan Liebgold" <Dan_member pathlink.com> wrote in message
news:b4ip35$ao7$1 digitaldaemon.com...
 Correct me if I'm wrong, but aren't multimethod dispatch methods always

some
 sort of runtime search at the time of the method call?

Yes.

 Even if the search is
 optimized by the compiler (to a binary search or somesuch), doesn't this
 implementational requirement cross the line in terms of performance?

It still should work out better than a sequence of if(dynamic_cast<...

yuqianzhou yahoo.co.uk writes:

In article <b4jrb6$cvc$2 digitaldaemon.com>, Walter says...
 Even if the search is
 optimized by the compiler (to a binary search or somesuch), doesn't this
 implementational requirement cross the line in terms of performance?

It still should work out better than a sequence of if(dynamic_cast<...

Great! Walter, sounds like you're interested in implementing multimethods in D?

If you keep your minds open like this, I'm sure D will have a bright future!

BTW, the following is what I wish to see before version 1.0:

-- Object persistence: save/load objects to/from memory/disk/network.

-- covariant (or anchored) type not just on function return type, but also on
parameters: e.g. even without template, we can still write the correct deepCopy
for any object as:

like this deepCopy(like this anObj);

(for anyone who read Eiffel, you know where I come from :-).

"Craig Black" <cblack ara.com> writes:

Hey peoples,

I would like to thank Mark Evans for his numerous contributions to this
mailing list.

Multi-methods are great!!

Implementation can be done in a number of ways.

O(1) complexity can be achieved by indexing types and storing an
N-Dimensional lookup table of function pointers.

If the memory footprint for the N-Dimensional table gets to be too large,
then you could store the function pointers in a binary tree.

If multi-methods are implemented correctly, they will enhance performance,
and save a lot of coding in many instances.  Writing your own
multiple-dispatch is a pain, and usually involves long switch statements
(yuck)!  I know from experience.

Craig

"Mike Wynn" <mike.wynn l8night.co.uk> writes:

"Craig Black" <cblack ara.com> wrote in message
news:b5o0du$iar$1 digitaldaemon.com...
 Hey peoples,

 I would like to thank Mark Evans for his numerous contributions to this
 mailing list.

 Multi-methods are great!!

 Implementation can be done in a number of ways.

 O(1) complexity can be achieved by indexing types and storing an
 N-Dimensional lookup table of function pointers.

 If the memory footprint for the N-Dimensional table gets to be too large,
 then you could store the function pointers in a binary tree.

why not compile the binary tree into a set of cmps and jmps ?

"Craig Black" <cblack ara.com> writes:

 why not compile the binary tree into a set of cmps and jmps ?

Hmmm ..... sounds difficult to implement but a good idea!

Craig

Ilya Minkov <midiclub 8ung.at> writes:

Craig Black wrote:
why not compile the binary tree into a set of cmps and jmps ?

 
 Hmmm ..... sounds difficult to implement but a good idea!

Why not optimise out all of the cmps and jmps altogether then. ;>

-i.

"Craig Black" <cblack ara.com> writes:

There is no way to "optimize out" the logic in the binary tree.  It must
exist in some form.  Somehow, the multi-method dispatcher is going to have
to find the method that corresponds to the identity of the objects it is
dealing with.  This can be done in a number of ways, none of which vaporize
into thin air when you optimize them.

Craig

"Ilya Minkov" <midiclub 8ung.at> wrote in message
news:b726ev$1ea5$1 digitaldaemon.com...
 Craig Black wrote:
why not compile the binary tree into a set of cmps and jmps ?

 Hmmm ..... sounds difficult to implement but a good idea!

 Why not optimise out all of the cmps and jmps altogether then. ;>

 -i.

"Craig Black" <cblack ara.com> writes:

I was just thinking, you could also use a hash table.

Craig