Two actors-related questions

[Peter Reiner Fels]

Hi.

I read the "Actors That Unify Threads and Events" paper and got two questions:

1) The paper says, that pattern matching expressions are partial functions.
When I look at the definition of PartialFunction, there should be an isDefinedAt(x : a)
and an apply(x : a) method. Two me a pattern matching expression does not look
like a PartialFunction. Does the Scala compiler know, that the first can be converted
to the second?

2) The papers also contains this code block:

loop { receive {
  case 'next => receive {
    case x: Option[_] => reply(x)
  }
}}

Does the 'next message have any special meaning? What does it mean when a message
starts with the ' character?

Regards,
  Peter

[bearfeeder]

Peter,

On 1/7/08, Peter Reiner Fels <prfels@...> wrote:

Hi.

I read the "Actors That Unify Threads and Events" paper and got two questions:

1) The paper says, that pattern matching expressions are partial functions.
When I look at the definition of PartialFunction, there should be an isDefinedAt(x : a)
and an apply(x : a) method. Two me a pattern matching expression does not look
like a PartialFunction. Does the Scala compiler know, that the first can be converted
to the second?

All {case ... => ...
      case ... => ...} are converted to partial functions by the compiler.
 

2) The papers also contains this code block:

loop { receive {
  case 'next => receive {
    case x: Option[_] => reply(x)
  }
}}

Does the 'next message have any special meaning? What does it mean when a message
starts with the ' character?

'next is a Symbol (an interned string)

Thanks,

David
 

Regards,
  Peter

--
lift, the secure, simple, powerful web framework http://liftweb.net
Collaborative Task Management http://much4.us

[Erik Engbrecht]

Peter,

Consider the following:

symbol match {

  case 'start => startDoingSomething()

  case 'stop => stopDoingSomething()

}

 

The above match statement is defined for the symbols 'start and 'stop, but not for any other objects.

 

As for the symbols, thy are just that - symbols.

 

http://www.scala-lang.org/docu/files/api/index.html

 

Symbols are pretty common in Lisp, (I think) Ruby, and probably other languages that use functional concepts.

 

-Erik
 

On 1/7/08, Peter Reiner Fels <prfels@...> wrote:

Hi.

I read the "Actors That Unify Threads and Events" paper and got two questions:

1) The paper says, that pattern matching expressions are partial functions.
When I look at the definition of PartialFunction, there should be an isDefinedAt(x : a)
and an apply(x : a) method. Two me a pattern matching expression does not look
like a PartialFunction. Does the Scala compiler know, that the first can be converted
to the second?

2) The papers also contains this code block:

loop { receive {
  case 'next => receive {
    case x: Option[_] => reply(x)
  }
}}

Does the 'next message have any special meaning? What does it mean when a message
starts with the ' character?

Regards,
  Peter

--
http://erikengbrecht.blogspot.com/

[Patrick Wright]

> > Does the 'next message have any special meaning? What does it mean when a
> message
> > starts with the ' character?
>
>
> 'next is a Symbol (an interned string)

Does anyone know where I can find documentation about how to use
symbols in Scala? I can't find any reference to it in the PinS book,
but have come across it in some code samples and have been wondering.


Thanks
Patrick

[steve.bendiola]

it is in section 1.3.7 of the Language spec
http://www.scala-lang.org/docu/files/ScalaReference.pdf
also in the scaladoc http://www.scala-lang.org/docu/files/api/scala/Symbol.html

I was surprised it wasn't in PINS

On Jan 7, 2008 2:26 PM, Patrick Wright <pdoubleya@...> wrote:

> > > Does the 'next message have any special meaning? What does it mean when a
> > message
> > > starts with the ' character?
> >
> >
> > 'next is a Symbol (an interned string)
>
> Does anyone know where I can find documentation about how to use
> symbols in Scala? I can't find any reference to it in the PinS book,
> but have come across it in some code samples and have been wondering.
>
>
> Thanks
> Patrick
>

[Fred Janon]

First time I hear about "Symbol"s as well.

What would be the use of "Symbol"s then? Use then like string constants without having to create a class and declare static fields for them?

Thanks

Fred

On Jan 8, 2008 5:49 AM, Steve Bendiola <steve.bendiola@...> wrote:

it is in section 1.3.7 of the Language spec
http://www.scala-lang.org/docu/files/ScalaReference.pdf
also in the scaladoc http://www.scala-lang.org/docu/files/api/scala/Symbol.html

I was surprised it wasn't in PINS

On Jan 7, 2008 2:26 PM, Patrick Wright <pdoubleya@...> wrote:
> > > Does the 'next message have any special meaning? What does it mean when a
> > message
> > > starts with the ' character?
> >
> >
> > 'next is a Symbol (an interned string)
>
> Does anyone know where I can find documentation about how to use
> symbols in Scala? I can't find any reference to it in the PinS book,
> but have come across it in some code samples and have been wondering.
>
>
> Thanks
> Patrick
>

[Viktor Klang]

Some parts of this message have been removed. Learn more about Nabble's security policy.

On 1/8/08, Fred Janon <fjanon@...> wrote:

First time I hear about "Symbol"s as well.

What would be the use of "Symbol"s then? Use then like string constants without having to create a class and declare static fields for them?

 

Signals for Actors is the first thing that strikes me...

 

santa !? 'Hohoho

Cheers,

-V

 

 

Thanks

Fred

On Jan 8, 2008 5:49 AM, Steve Bendiola <steve.bendiola@...> wrote:

it is in section 1.3.7 of the Language spec
http://www.scala-lang.org/docu/files/ScalaReference.pdf
also in the scaladoc http://www.scala-lang.org/docu/files/api/scala/Symbol.html

I was surprised it wasn't in PINS

On Jan 7, 2008 2:26 PM, Patrick Wright <pdoubleya@...> wrote:

> > > Does the 'next message have any special meaning? What does it mean when a
> > message
> > > starts with the ' character?
> >
> >
> > 'next is a Symbol (an interned string)
>
> Does anyone know where I can find documentation about how to use
> symbols in Scala? I can't find any reference to it in the PinS book,
> but have come across it in some code samples and have been wondering.
>
>
> Thanks
> Patrick
>

 

--
_____________________________________
/                                                                 \
        /lift/ committer ( www.liftweb.net)
      SGS member (Scala Group Sweden)
  SEJUG member (Swedish Java User Group)
\_____________________________________/