On Feb 7, 2015, at 12:55 PM, Hern��n Morales Durand <hernan.morales@gmail.com> wrote:

Hi Eliot,

2015-02-07 14:48 GMT-03:00 Eliot Miranda <eliot.miranda@gmail.com>:

Hi Hernan,

On Sat, Feb 7, 2015 at 7:41 AM, Hern��n Morales Durand <hernan.morales@gmail.com> wrote:

2015-02-07 5:59 GMT-03:00 kilon alios <kilon.alios@gmail.com>:
Personally I don't like Pragmas, they have not convinced me so far that they fit the style of Smalltalk syntax. I have to confess though I never liked descriptive elements and languages .

Me neither. Actually the pragma idea is not wrong per se, it is the tag syntax to write them which bothers me. Because the world can be described with tags if you start that path.

How exactly is the syntax wrong?

I am not saying syntax is wrong, I just don't like it because:

1) Adds another level of representation inside an already reflective system.

2) It could be done with plain common message sends.

No it can't. Common sends are executable and we don't want pragmas executed when the method is run, we want the pragma executed when the method is added, or analysed. That was what was ugly about the use of plain sends in e.f. VMMaker, that there had to be lots of empty implementations of the messages used for metadata.

So using normal sends

- prevents the metadata from being directly executed because executing them when the method is run is wrong

- confuses meta level and normal level, putting them at the same level, and hence...

- confusing for the programmer because its not obvious what's metadata and what's a normal send

- makes analysis harder for the same reason

3) Should be (to me) "hidden" from method pane, and displayed by a specific tool inside the system browser.

I disagree. I want to see the pragma. It has essential information that shouldn't be hidden. I want to edit it easily. And how can you in the one hand say it can be implemented as a normal message send a d at the same time want it hidden? Be consistent :-)

The <literalMessagePattern> syntax predates pragmas. It was used first for numeric primitives in Smalltalk-76 or Smalltalk-80. Squeak extended it with primitive:module:. I and others extended it to include arbitrary literal message patterns. The syntax of a literal message pattern is the syntax of a send with no receiver and only literal arguments.
The use of this syntax means
a) no new syntax
b) each pragma is potentially executable
c) methods using specific pragmas can be found using "find senders"
d) the execution side of a pragma can be found using "find implementors"

So what's wrong with that? How is it wrong to use a common Smalltalk object, a Message, that is well-supported in the system, for method metadata?

I get that pragmas are messages, but they assume an implicit receiver, which actually depends on context. If I understood right with pragmas always receiver = destination?

Not for pragmas that are just labels. And what's destination? In the menu building example above the destination"is the menu but the receiver is the menu builder. So I think that what the receiver is depends on usage.

If you change things in the communication model (receiver, sender, message, etc.), by removing or adding elements, you have a loss in the message because it gets harder to reconstruct the message send.

I don't understand this. Can you expand?

Consider

<eventRegistration>
| eventRegistration |
{ eventRegistration }.
self eventRegistration.

which of them "it sounds like" you cannot infer their purpose?

I don't get the example, because of the confusion of meta layers.

says "this is metadata"

| eventRegistration |

says "this is a bug in the method because the variable isn't used, and eg Opal will remove it so it won't be there".

{ eventRegistration }.

I guess you mean { #eventRegistration }. If so this is the same. An optimizing compiler will delete it.

self eventRegistration.

says "send myself eventRegustration". Which /isn't/ what's wanted.

So for me only the pragma implies "this method is to be registered with the event system". The middle two say "I am a bug, or syntax error". The last one says "I am a normal send".

To me the first because you need the context MyClass>>methodName
and you need to browse the pragma to get its purpose.

There are other ways to add metadata to methods. Without tagging.

Haven't we discussed that? Putting metadata off to the side introduces a bookkeeping problem. It is a bad idea.

Yes, but I still have a lot of doubts about feedback with pragmas (I hope you view them as constructive criticism).

I'm finding this whole conversation exhausting.

Is like pragmas assume there is always a perfect message transaction.
How can I halt the execution of a specific pragma?

By putting a break point in its implementations.

Can I write <myPragma halt>?

No. But you can out a conditional breakpoint in CompiledMethod>>pragmaAt: or in the pragma's implementation.

How do I know if it will get executed?

By reading the broader system or adding break pints as just described.

Is <shortcut> a functional pragma?
How do I distinguis any pragma from being functional or "documentation"?

Using "implementors" and "senders" you can find out where it may be used. One if the problems of late-bound systems is figuring out what binds to what. Pragmas are more difficult to figure out unless pragmas have clearly commented implementations.

And they don't need to be in the method pane itself.

For some kinds of metadata, for metadata with semantics, not just a documentary function, it is important for the metadata to be obvious.

I think this depends on context. Because your work could be towards low-level machinery details or software reenginering, doesn't mean that we all need to view compiler directives, functional and structural annotations, etc.

That's a mischaracterisation. Most of their uses are for pluggable GUIs. And if this is so onerous why weren't you protesting <primitive: 123>?

And if I can write some prediction... When someone invents automatic annotation (like happens now with genomes) and decides it will be cool to have them in the image (because you will gain performance, more reflective capabilitites, etc) methods could explode with pragmas to the point gets to be annoying to browse any method. Then the tool will have to be built by need.

No one has argued for hiding the primitive specification off-to-the-side. "Need" is a poor criticism here because using turing equivalence lots of things don't "need" to be the way they are. Instead why not ask what are the pros and cons?

Ok, many of us knows the pros. I have been using pragmas for a while.
But if we stop discussing then it will never adapt to new ideas.
So you may want to share your view of cons too :)

The cons are that for years, and at length, one has to defend a good idea ;-). Pragmas were a new idea and here in thus conversation we see how resistant we are to new ideas. I've seen nothing against the need for per-method metadata and a lot on how it can be done with other mechanisms. But the existing mechanisms don't do one of two things

- separate normal from meta levels

- obviously associate metadata with methods.

So what I'm missing in this conversation is addressing the issues:

- how in a componentised loadable system do we decouple component loads where components collide in areas like global menu definitions, inspectors, etc?

- how do we associate metadata with methods so that

- the metadata is of a form that fits well with the host system?

- the metadata is clearly associated with the method it is data of?

- the bookkeeping is managed?

You could add good questions here. But these are the questions I was thinking of when we added pragmas to VW.

It is like having to specify protocol because there is no list pane to create them.

I disagree. When the pragma is specifying type information, specifying that the method is an action on a specific menu, is a pane in an inspector, and many other uses, it is essential that that information be represented, and putting it in a one-off bookkeeping system is a bad idea. We're not talking about simple documentary metadata like author, category etc.

Well, I think documentary metadata is tremendously complex.

We're using pragmas for semantics, semantics of the method that are outside of its execution semantics, semantics about how the method fits in the broader system. And putting that in non-obvious places is a bad idea.

I agree. But obvious could be a place where can be located by a method though not necessarily visible.

Cheers,

Hern��n

Hern��n

About python decorators I disagree that are similar to pragmas. Pragmas are focused on being descriptive , python decorators are descriptive as by product. The main focus of python decorators is to shorten code by introducing syntactic sugar.

Kilon, pragmas are not limited to being descriptive.

I agree though this is a very interesting discussion and I dont understand most of the things stated here so I leave an open door and mind for pragmas. Maybe one day I will "get it".

That would be nice :)

On Sat, Feb 7, 2015 at 10:02 AM, Thierry Goubier <thierry.goubier@gmail.com> wrote:

2015-02-06 22:00 GMT+01:00 stepharo <stepharo@free.fr>:
Really interesting discussion. I like pragmas but this is interesting to see them challenged.

Thanks. It's a pleasure to discuss that way :)

Yes, but there end up being lots of naming conventions and they are non-obvious. Whereas pragmas, because they are in-your-face in the methods in question, don't need conventions. They just need documenting ;-).

Thierry I'm skeptical that multiple protocol will save the problem because you will rely on coding conventions.

Pragma as well: just explain the conventions behind the gtInspector pragmas, for example.

But give me multiple protocols and I'll show you the same conventions rewritten in less lines (and a slightly more efficient code).

And pragma is a clever tagging.

Then maybe we should remove protocols and replace them with pragmas :)

Thierry

Stef

--
best,
Eliot