a simple introduction to scala's continuation support, not thorough enough.

1. continuations in
fujohnwang
@Twitter
@weibo
Saturday, July 9, 2011

2. what’s continuation?
Continuation capture the state of a
computation(maybe to be invoked later).
Simple concept, but hard to get.
first-class support in schema language
Saturday, July 9, 2011

3. know CPS first
normal control flow structure
control flow structure after cps
PS.
code
sample
borrowed
from
http://www.slideshare.net/openbala/continuations
Saturday, July 9, 2011

4. WHat’s the big deal?
Saturday, July 9, 2011

5. usage scenarios
programming design pattern
coroutine
exception handling
web frameworks
backtracking
Saturday, July 9, 2011

6. observer pattern with
continuation
Saturday, July 9, 2011

7. Coroutine?
see the blog of jim mcbeatch
Saturday, July 9, 2011

8. Exception handling
No sample code yet
Saturday, July 9, 2011

9. Web Framework
with continuation support
seaside / smalltalk
cocoon / Java
http://cocoon.apache.org/2.1/userdocs/flow/continuations.html
weblocks / common lisp
wee / ruby
ocsigen / ocaml
more...
Saturday, July 9, 2011

10. Saturday, July 9, 2011

11. code pieces
function calculator()
{
var a, b, operator;
cocoon.sendPageAndWait("getA.html");
a = cocoon.request.get("a");
cocoon.sendPageAndWait("getB.html");
b = cocoon.request.get("b");
cocoon.sendPageAndWait("getOperator.html");
operator = cocoon.request.get("op");
try {
if (operator == "plus")
cocoon.sendPage("result.html", {result: a + b});
else if (operator == "minus")
cocoon.sendPage("result.html", {result: a - b});
else if (operator == "multiply")
cocoon.sendPage("result.html", {result: a * b});
else if (operator == "divide")
cocoon.sendPage("result.html", {result: a / b});
else
cocoon.sendPage("invalidOperator.html", {operator: operator});
}
catch (exception) {
cocoon.sendPage("error.html", {message: "Operation failed: " + exception.toString
()});
}
Saturday,} 9, 2011
July

12. Continuation types
full continuation(aka. first-class cont.)
delimited continuation (aka. partial, composable cont.)
write async code as sequence one
mix cps code and normal code seamlessly
Saturday, July 9, 2011

13. What DC looks like?
reset
{
reset
{
println(1)
println(1)
shift
{
cont
=>
shift
{
cont
=>
}
println(2)
println(2)
}
}
println(3)
//prints:
1
}
//prints:
1
2
reset
{
println(1)
def
is123(n:Int):Boolean
=
{
shift
{
cont
=>
reset
{
cont()
shift
{
k
:
(Int=>String)
=>
println(2)
(k(n)
==
"123")
}
}.toString
println(3)
} }
} //prints:
1
3
2
Saturday, July 9, 2011

14. first glance with dc
reset and shift
reset sets up the boundary of dc(‘s cps)
shift captures the continuation
Result types
yield
return
Saturday, July 9, 2011

15. puzzle about
yield and return
Saturday, July 9, 2011

16. scala cont features
compiler plugin + Library
compiler plugin does cps transformation
library supports control structures and directives
serializable (can be saved, distribute sys...)
see swarm?!
Others?
Saturday, July 9, 2011

17. available softwares
swarm
scalaflow
Akka’s DataFlow Concurrency library
nio actor implementation for akka
nioserver
Saturday, July 9, 2011

18. What I want to do with it
coroutine
combine with java nio
resource-efficient minimally-threaded
networking layer framework
reduce hw cost finally
Saturday, July 9, 2011

19. Questions?
Saturday, July 9, 2011

20. References
http://www.scala-lang.org/node/2096
http://okmij.org/ftp/continuations/Continuations.html
http://jim-mcbeath.blogspot.com/2010/08/delimited-continuations.html
http://lamp.epfl.ch/~rompf/continuations-icfp09.pdf
http://okmij.org/ftp/continuations/index.html
http://suereth.blogspot.com/2010/03/how-you-should-think-about-delimited.html
http://dcsobral.blogspot.com/2009/07/delimited-continuations-explained-in.html
http://blog.richdougherty.com/2009/02/delimited-continuations-in-scala_24.html
http://en.wikipedia.org/wiki/Seaside_(software)
http://en.wikipedia.org/wiki/Call-with-current-continuation
http://community.schemewiki.org/?call-with-current-continuation-for-C-programmers
http://community.schemewiki.org/?call-with-current-continuation
http://en.wikipedia.org/wiki/Coroutine
http://cocoon.apache.org/2.1/userdocs/flow/continuations.html
https://github.com/rschildmeijer/loft
Saturday, July 9, 2011

21. Thanks
Saturday, July 9, 2011