Re: An IDL for SCXML interpreters

--Apple-Mail=_667083EC-150B-4DAA-A55A-FF964E63F47A
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain;
	charset=utf-8

Sorry, forgot to send to the list.

Le 3 juil. 2015 =C3=A0 16:01, Stefan Radomski =
<[email protected] =
<mailto:[email protected]>> a =C3=A9crit :
>=20
> [explicitly bcc'ing David, Jacob and Zjnue for I know that they =
maintain SCXML implementations] - this post is pertaining to action =
point 1 from my previous mail:
>=20
> 1. An Interface Description Language (IDL) for SCXML interpreters.

You can keep your various FromXXX methods as optional, but please allow =
an overloaded constructor for languages that aren't JAVA :p
So, define the constructor's behavior for DOM, XML string, and URI =
arguments, leaving room for other types (e.g. File in JSSC).


> 1.1 For simple life-cycle and interpretation of state-charts.
> 1.2 A set of hooks for (on-line) visualisation.
> 1.3 A set of hooks for (on-line) modelling / debugging.
>=20
> For now, I'd like to focus on point 1.1, but we ought to keep the =
others in mind and maybe eventually extend our ambitions. At least 1.2 =
is very useful as it would allow or a common visualisation. I hereby =
propose a first sketch for an Interface Description Language (IDL) for =
SCXML (see below). It will only allow to instantiate interpreters, run =
them and deliver events. A typical session would look like this:
>=20
> import namespace scxml;
> try {
> Interpreter session =3D Implementation.fromURI("http://www =
<http://www/>.example.com/foo.scxml <http://example.com/foo.scxml>");
> for(;;) {
> int state =3D session.step();
> if (state =3D=3D FINISHED)
> break;
> if (state =3D=3D AFTER_MACROSTEP && session.configuration.in('foo'))
> session.receive('bar.baz');
> }
> } catch (Exception e) {
> print e;
> }

That may be "typical" but it's impossible in EcmaScript, which has very =
few blocking calls.


> =3D=3D 1. Threads
> I want to avoid any assumptions about the availability of threads in =
the embedding platform. As such, there is e.g. no non-blocking =
interpret(). It would be the responsibility of the target platform to =
emulate something like this by embedding the block above in a thread.

ECMAScript itself does not use threads. However, the APIs and libraries =
it can use tend to use threads internally (e.g. network, filesystem, =
data encoding/decoding=E2=80=A6) and the language deals with it by using =
callbacks, often wrapped in event handlers or Promises.

As a result, a typical ECMAScript session would look more like:

require(SCXML)

session =3D new SCXML("foo.scxml")
session.ready.then(session.start.bind(session))
session.on("step", () =3D> { if(session.configuration.has('foo')) =
session.receive('bar.baz') })

I suggest specifying both a blocking IDL and a Promise one, =
implementations being free to implement either (but not both at once =
because methdos would have the same name), and an Event IDL (which can =
work with both).

E.g in async mode a method like step() returns a Promise that resolves =
when the macrostep is done. In blocking mode it returns when the =
macrostep is done. We can't have both. Don't even think of stepAsync(). =
An implementation that supports both might allow some configuration to =
switch modes, but really, I don't see it being useful. And in either =
case you could have session.on("done").


> =3D=3D 2. Exceptions
> Similarly I want to avoid any assumption about the availability of =
exceptions, therefore step() might return FAULT and set the lastError =
attribute:
>=20
> int state;
> for(;;) {
> state - session.step();
> switch(state) {
> case FAULT:
> print session.lastError;
> break;
> case FINISHED:
> return;
> }
> }

Again, the assumption that blocking is always available is false. As =
before, write a blocking IDL, a Promise IDL (Promises can reject with an =
error), and an event IDL with on("error") conditions.


> =3D=3D 3. Data
> 0. If nothing in a Data object is set, its value is undefined

OK.

> 1. If an atom is given, the respective field is to be interpreted as =
the evaluation of that atom, e.g. "3" is a string, 3 is an integer.

evaluation how? JSON? how about an optional type attribute on <content> =
/ <data> that I've suggested before?

> 2. If a node is given and 1. is not the case, the field is to be =
represented as a DOM Node

How about multiple node children?

> 3. If a key in a compound is set and 1. and 2. are not the case, the =
respective field is a map

Can you give an example for that one?

> 4. If an index is set and none of the above applies, the respective =
field is an array. Setting a an item at an index N will cause the array =
to behave as if it has N fields for the largest N. With all unset fields =
undefined.

What's the difference between indices and keys? In ES, indices are just =
positive integer keys.
I'd say that an array is when you have multiple children with no =
keys/indices at all.

> =3D=3D 6. Naming
> AFTER_MACROSTEP might just as well be called STABLE. I choose the =
former for its more explicit reference to the runtime semantics of =
SCXML, which might play a role if we were to specify a bunch of hooks =
for 1.2 and 1.3 (see debugger paper[1], table 1)

I feel that "stable" should be used only when the queue is empty. =
Otherwise it's not going to remain stable even one moment.


Sorry, I'll have to continue later.


			David


--Apple-Mail=_667083EC-150B-4DAA-A55A-FF964E63F47A
Content-Transfer-Encoding: quoted-printable
Content-Type: text/html;
	charset=utf-8

<html><head><meta http-equiv=3D"Content-Type" content=3D"text/html =
charset=3Dutf-8"></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D"">Sorry, forgot to send to the list.<br class=3D""><div><br =
class=3D""><div class=3D""><div class=3D"">Le 3 juil. 2015 =C3=A0 16:01, =
Stefan Radomski &lt;<a =
href=3D"mailto:[email protected]" =
class=3D"">[email protected]</a>&gt; a =C3=A9crit =
:</div><div class=3D""><div style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D""><div class=3D""><blockquote type=3D"cite" class=3D""><br =
class=3D"Apple-interchange-newline"><div class=3D"">

<meta http-equiv=3D"Content-Type" content=3D"text/html; =
charset=3Dus-ascii" class=3D"">

<div style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; =
-webkit-line-break: after-white-space;" class=3D"">[explicitly bcc'ing =
David, Jacob and Zjnue for I know that they maintain SCXML =
implementations] - this post is pertaining to action point 1 from my =
previous mail:<br class=3D"">
<br class=3D"">
1. An Interface Description Language (IDL) for SCXML interpreters.<br =
class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">You can keep your various FromXXX =
methods as optional, but please allow an overloaded constructor for =
languages that aren't JAVA :p</div><div class=3D"">So, define the =
constructor's behavior for DOM, XML string, and URI arguments, leaving =
room for other types (e.g. File in JSSC).</div><div class=3D""><br =
class=3D""></div><br class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D""><div style=3D"word-wrap: break-word; -webkit-nbsp-mode: =
space; -webkit-line-break: after-white-space;" class=3D"">
1.1 For simple life-cycle and interpretation of state-charts.<br =
class=3D"">
1.2 A set of hooks for (on-line) visualisation.<br class=3D"">
1.3 A set of hooks for (on-line) modelling / debugging.<br class=3D"">
<br class=3D"">
For now, I'd like to focus on point 1.1, but we ought to keep the others =
in mind and maybe eventually extend our ambitions. At least 1.2 is very =
useful as it would allow or a common visualisation. I hereby propose a =
first sketch for an Interface Description
 Language&nbsp;(IDL) for SCXML (see below). It will only allow to =
instantiate interpreters, run them and deliver events. A typical session =
would look like this:<br class=3D"">
<br class=3D"">
import namespace scxml;<br class=3D"">
try {<br class=3D"">
<span class=3D"Apple-tab-span" =
style=3D"white-space:pre"></span>Interpreter session =3D =
Implementation.fromURI("<a href=3D"http://www/" =
class=3D"">http://www</a>.<a href=3D"http://example.com/foo.scxml" =
class=3D"">example.com/foo.scxml</a>");<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>for(;;) =
{<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>int =
state =3D session.step();<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>if =
(state =3D=3D FINISHED)<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>break;<br =
class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>if =
(state =3D=3D AFTER_MACROSTEP &amp;&amp; =
session.configuration.in('foo'))<br class=3D"">
<span class=3D"Apple-tab-span" =
style=3D"white-space:pre"></span>session.receive('bar.baz');<br =
class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>}<br =
class=3D"">
} catch (Exception e) {<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>print =
e;<br class=3D"">
}<br class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">That may be "typical" but it's =
impossible in EcmaScript, which has very few blocking calls.</div><div =
class=3D""><br class=3D""></div><br class=3D""><blockquote type=3D"cite" =
class=3D""><div class=3D""><div style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D"">=3D=3D 1. Threads<br class=3D"">
I want to avoid any assumptions about the availability of threads in the =
embedding platform. As such, there is e.g. no non-blocking interpret(). =
It would be the responsibility of the target platform to emulate =
something like this by embedding the block above&nbsp;in
 a thread.<br class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">ECMAScript itself does not use threads. =
However, the APIs and libraries it can use tend to use threads =
internally (e.g. network, filesystem, data encoding/decoding=E2=80=A6) =
and the language deals with it by using callbacks, often wrapped in =
event handlers or Promises.</div><div class=3D""><br class=3D""></div><div=
 class=3D"">As a result, a typical ECMAScript session would look more =
like:</div><div class=3D""><br class=3D""></div><div =
class=3D"">require(SCXML)</div><div class=3D""><br class=3D""></div><div =
class=3D"">session =3D new SCXML("foo.scxml")<span =
id=3D"x-apple-selection:end" class=3D""></span></div><div =
class=3D"">session.ready.then(session.start.bind(session))</div><div =
class=3D"">session.on("step", () =3D&gt; { =
if(session.configuration.has('foo')) session.receive('bar.baz') =
})</div><div class=3D""><br class=3D""></div><div class=3D"">I suggest =
specifying both a blocking IDL and a Promise one, implementations being =
free to implement either (but not both at once because methdos would =
have the same name), and an Event IDL (which can work with =
both).</div><div class=3D""><br class=3D""></div><div class=3D"">E.g in =
async mode a method like step() returns a Promise that resolves when the =
macrostep is done. In blocking mode it returns when the macrostep is =
done. We can't have both. Don't even think of stepAsync(). An =
implementation that supports both might allow some configuration to =
switch modes, but really, I don't see it being useful. And in either =
case you could have session.on("done").</div><div class=3D""><br =
class=3D""></div><div class=3D""><br class=3D""></div><blockquote =
type=3D"cite" class=3D""><div class=3D""><div style=3D"word-wrap: =
break-word; -webkit-nbsp-mode: space; -webkit-line-break: =
after-white-space;" class=3D"">=3D=3D 2. Exceptions<br class=3D"">
Similarly I want to avoid any assumption about the availability of =
exceptions, therefore step() might return FAULT and set the lastError =
attribute:<br class=3D"">
<br class=3D"">
int state;<br class=3D"">
for(;;) {<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>state - =
session.step();<br class=3D"">
<span class=3D"Apple-tab-span" =
style=3D"white-space:pre"></span>switch(state) {<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>case =
FAULT:<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>print =
session.lastError;<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>break;<br =
class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>case =
FINISHED:<br class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>return;<br=
 class=3D"">
<span class=3D"Apple-tab-span" style=3D"white-space:pre"></span>}<br =
class=3D"">
}<br class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">Again, the assumption that blocking is =
always available is false. As before, write a blocking IDL, a Promise =
IDL (Promises can reject with an error), and an event IDL with =
on("error") conditions.</div><div class=3D""><br class=3D""></div><div =
class=3D""><br class=3D""></div><blockquote type=3D"cite" class=3D""><div =
class=3D""><div style=3D"word-wrap: break-word; -webkit-nbsp-mode: =
space; -webkit-line-break: after-white-space;" class=3D"">

=3D=3D 3. Data<br class=3D"">
0. If nothing in a Data object is set, its value is =
undefined</div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">OK.</div><br class=3D""><blockquote =
type=3D"cite" class=3D""><div class=3D""><div style=3D"word-wrap: =
break-word; -webkit-nbsp-mode: space; -webkit-line-break: =
after-white-space;" class=3D"">
1. If an atom is given, the respective field is to be interpreted as the =
evaluation of that atom, e.g. "3" is a string, 3 is an integer.<br =
class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">evaluation how? JSON? how about an =
optional type attribute on &lt;content&gt; / &lt;data&gt; that I've =
suggested before?</div><br class=3D""><blockquote type=3D"cite" =
class=3D""><div class=3D""><div style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D"">
2. If a node is given and 1. is not the case, the field is to be =
represented as a DOM Node</div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">How about multiple node =
children?</div><br class=3D""><blockquote type=3D"cite" class=3D""><div =
class=3D""><div style=3D"word-wrap: break-word; -webkit-nbsp-mode: =
space; -webkit-line-break: after-white-space;" class=3D"">
3. If a key in a compound is set and 1. and 2. are not the case, the =
respective field is a map<br class=3D""></div></div></blockquote><div =
class=3D""><br class=3D""></div><div class=3D"">Can you give an example =
for that one?</div><br class=3D""><blockquote type=3D"cite" =
class=3D""><div class=3D""><div style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" =
class=3D"">
4. If an index is set and none of the above applies, the respective =
field is an array. Setting a an item at an index N will cause the array =
to behave as if it has N fields for the largest N. With all unset fields =
undefined.<br class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">What's the difference between indices =
and keys? In ES, indices are just positive integer keys.</div><div =
class=3D"">I'd say that an array is when you have multiple children with =
no keys/indices at all.</div><div class=3D""><br =
class=3D""></div><blockquote type=3D"cite" class=3D""><div class=3D""><div=
 style=3D"word-wrap: break-word; -webkit-nbsp-mode: space; =
-webkit-line-break: after-white-space;" class=3D"">=3D=3D 6. Naming<br =
class=3D"">
AFTER_MACROSTEP might just as well be called STABLE. I choose the former =
for its more explicit reference to the runtime semantics of SCXML, which =
might play a role if we were to specify a bunch of hooks for 1.2 and 1.3 =
(see debugger paper[1], table&nbsp;1)<br =
class=3D""></div></div></blockquote><div class=3D""><br =
class=3D""></div><div class=3D"">I feel that "stable" should be used =
only when the queue is empty. Otherwise it's not going to remain stable =
even one moment.</div><div class=3D""><br class=3D""></div><br =
class=3D""></div><div class=3D"">Sorry, I'll have to continue =
later.</div><div class=3D""><br class=3D""></div><br class=3D""><div =
class=3D""><span class=3D"Apple-tab-span" style=3D"white-space:pre">		=
	</span>David</div></div></div></div></div><br =
class=3D""></body></html>=

--Apple-Mail=_667083EC-150B-4DAA-A55A-FF964E63F47A--