Hello Ben!
the following:
val square = (x:Int) => x * x
"val square" is the equivalent of a "final" reference in Java.
(x : Int) => x * x
This constructs a Function instance that takes an Int and returns that Int
squared.
The equivalent Java code would be something like:
interface Function<R,P> //We're ignoring variance here, as to not confuse
{
public R call(P p);
}
final Function<Integer,Integer> square = new Function<Integer,Integer>() {
public Integer call(Integer i)
{
return i * i;
}
}
And then you can do:
square.call(2) // 4
So, back to Scala:
val square = (x : Int) => x * x
square(2) // 4
On Thu, Jul 30, 2009 at 9:37 PM, ben <b...@primrose.org.uk> wrote:
>
> Hi,
>
> I feel I must apologise for this post ... I've only been doing scala
> for a week, and lift for 3 days, but I'm stuck.
> I'm coming from an experienced java background, just struggling with
> some scala constructs.
>
> I feel I understand the basics of lambda and function literals - but
> I'm blown away by some of the syntax in the lift "Getting Started"
> tutorial.
> For example, given :
>
> val mylist = Array(1,2,3)
> mylist..foreach(v => println(v)
>
> Here I understand where "v" comes from - its each int in the list.
>
> In the tutorial (http://liftweb.net/docs/getting_started/
> mod_master.html<http://liftweb.net/docs/getting_started/%0Amod_master.html>
> )
> there is a function "desc" (Listing 15) :
>
> private def desc(td: ToDo, reDraw: () => JsCmd) =
> swappable(<span>{td.desc}</span>,
> <span>{ajaxText(td.desc,
> v => {td.desc(v).save; reDraw()})}
> </span>)
>
> For my own brain to try and "break it down", I have :
>
> private def desc(td: ToDo, reDraw: () => JsCmd) = {
> val myFunctionLiteral = (xxx: String) => {td.desc(xxx).save;
> println("!!!!!!!!!Desc function :" + xxx); reDraw()}
>
> swappable(<span>{td.desc}</span>,
> <span>{ajaxText(td.desc, myFunctionLiteral)}</span>)
> }
>
> This is called from the "doList" method :
>
> private def doList(reDraw: () => JsCmd)(html: NodeSeq): NodeSeq =
> toShow.
> flatMap(td =>
> bind("todo", html,
> "desc" -> desc(td, reDraw)
> ))
>
> I understand where the "ToDo" object "td" is coming from, and how the
> "reDraw" thing works, and how they are passed to the "desc" function,
> but what I don't understand at all is where the val "xxx" in
> "myFunctionLiteral" comes from ?
> How is it passed into the function ? Is it currying ?
>
> I'm sorry for such a vague question, I'm totally at sea here.
>
> Thankyou for reading this, and for any help you may provide !
>
> Ben
>
> >
>
--
Viktor Klang
Rogue Scala-head
Blog: klangism.blogspot.com
Twttr: viktorklang
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