Continuations in scala （incomplete version）

continuations in

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Saturday, July 9, 2011

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


know CPS first

normal control flow structure

control flow structure after cps

PS. code sample borrowed from http://www.slideshare.net/openbala/continuations


http://www.slideshare.net/openbala/continuations

http://www.slideshare.net/openbala/continuations

WHat’s the big deal?


usage scenarios

programming design pattern

coroutine

exception handling

web frameworks

backtracking？


observer pattern with continuation


Coroutine?

see the blog of jim mcbeatch


Exception handling

No sample code yet


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



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, July 9, 2011

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


What DC looks like?

def is123(n:Int):Boolean = { reset { shift { k : (Int=>String) => (k(n) == "123") }.toString } }

reset { println(1) shift { cont => } println(2)}//prints: 1

reset { println(1) shift { cont => println(2) } println(3)}//prints: 1 2

reset { println(1) shift { cont => cont() println(2) } println(3)}//prints: 1 3 2


first glance with dcreset and shift

reset sets up the boundary of dc(‘s cps)

shift captures the continuation

Result types

yield

return


puzzle about yield and return


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?


available softwares

swarm

scalaflow

Akka’s DataFlow Concurrency library

nio actor implementation for akka

nioserver


What I want to do with it

coroutine

combine with java nio

resource-efficient minimally-threaded networking layer framework

reduce hw cost finally


Questions?


Referenceshttp://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


https://github.com/rschildmeijer/loft


http://www.scala-lang.org/node/2096

http://www.scala-lang.org/node/2096















http://en.wikipedia.org/wiki/Seaside_(software

http://en.wikipedia.org/wiki/Seaside_(software













Thanks


Continuations in scala （incomplete version）

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