Yes, you can lift your collection to a function `Int =&gt; Option[A]`:

    scala&gt; List(1,2,3).lift
    res0: Int =&gt; Option[Int] = &lt;function1&gt;

    scala&gt; List(1,2,3).lift(9)
    res1: Option[Int] = None

If I have a block of HTML with many tags, how do insert it in JavaScript?

    var div = document.createElement(&#39;div&#39;);
    div.setAttribute(&#39;class&#39;, &#39;post block bc2&#39;);
    div.innerHTML = &#39;HERE TOO MUCH HTML that is much more than one line of code&#39;;
    document.getElementById(&#39;posts&#39;).appendChild(div);

How do I do it right?

How to insert a large block of HTML in JavaScript?

I am using Twitter Bootstrap to create collapsible sections of text. The sections are expanded when a `+` button  is pressed. My html code as follows:

    &lt;div class=&quot;row-fluid summary&quot;&gt;
	    &lt;div class=&quot;span11&quot;&gt;
	        &lt;h2&gt;MyHeading&lt;/h2&gt;	
	    &lt;/div&gt;
	    &lt;div class=&quot;span1&quot;&gt;
	        &lt;button type=&quot;button&quot; class=&quot;btn btn-success&quot; data-toggle=&quot;collapse&quot; data-target=&quot;#intro&quot;&gt;+&lt;/button&gt;
	    &lt;/div&gt;
    &lt;/div&gt;
    &lt;div class=&quot;row-fluid summary&quot;&gt;
    	&lt;div id=&quot;intro&quot; class=&quot;collapse&quot;&gt; 
	        Here comes the text...
    	&lt;/div&gt;
    &lt;/div&gt;

Is there a way to change the button to display `-` instead of `+` after the section is expanded (and change back to `+` when it is collapsed again)?

**Additional information**: I hoped there would be a simple twitter-bootstrap/css/html-based solution to my problem. All responses so far make use of JavaScript or PHP. Because of this I want to add some more information about my development environment: I want to use this solution inside a SilverStripe-based (version 3.0.5) website which has some implications for the use of both PHP as well as JavaScript.

Twitter bootstrap collapse: change display of toggle button

Is there a way, only using the Scala collection API, to get an Option in a List when trying to get an element by its index?


I&#39;m looking for the equivalent of this function, does it exist?

   

    def optionalValue[T](l: List[T], index: Int) = {
      if (l.size &lt; (index+1)) None 
      else Some(l(index))
    }

Thanks

How to get an Option from index in Collection in Scala?

Is there a way, only using the Scala collection API, to get an Option in a List when trying to get an element by its index?
I'm looking for the equivalent of this function, does it exist?
<pre><code class="hljs language-scss">def optionalValue[T](l: List[T], index: Int) = {
 if (l.size &#x3C; (index+1)) None 
 else Some(l(index))
}
</code></pre>
Thanks

Suppose I have several futures and need to wait until _either_ any of them fails _or_ all of them succeed. 

For example: Let there are 3 futures: `f1`, `f2`, `f3`. 

* If `f1` succeeds and `f2` fails I do not wait for `f3` (and return _failure_ to the client). 

* If `f2` fails while `f1` and `f3` are still running I do not wait for them (and return _failure_) 

* If `f1` succeeds and then `f2` succeeds I continue waiting for `f3`.

How would you implement it?

How to wait for several Futures?

I wanted to memoize this:

    def fib(n: Int) = if(n &lt;= 1) 1 else fib(n-1) + fib(n-2)
    println(fib(100)) // times out

So I wrote this and this surprisingly compiles and works (I am surprised because `fib` references itself in its declaration):

    case class Memo[A,B](f: A =&gt; B) extends (A =&gt; B) {
      private val cache = mutable.Map.empty[A, B]
      def apply(x: A) = cache getOrElseUpdate (x, f(x))
    }
    
    val fib: Memo[Int, BigInt] = Memo {
      case 0 =&gt; 0
      case 1 =&gt; 1
      case n =&gt; fib(n-1) + fib(n-2) 
    }

    println(fib(100))     // prints 100th fibonacci number instantly

But when I try to declare fib inside of a `def`, I get a compiler error:

    def foo(n: Int) = {
      val fib: Memo[Int, BigInt] = Memo {
        case 0 =&gt; 0
        case 1 =&gt; 1
        case n =&gt; fib(n-1) + fib(n-2) 
      }
      fib(n)
    } 

Above fails to compile `error: forward reference extends over definition of value fib
case n =&gt; fib(n-1) + fib(n-2)`

Why does declaring the `val fib` inside a def fails but outside in the class/object scope works?

To clarify, why I might want to declare the recursive memoized function in the def scope - here is my solution to the subset sum problem:

  

    /**
       * Subset sum algorithm - can we achieve sum t using elements from s?
       *
       * @param s set of integers
       * @param t target
       * @return true iff there exists a subset of s that sums to t
       */
      def subsetSum(s: Seq[Int], t: Int): Boolean = {
        val max = s.scanLeft(0)((sum, i) =&gt; (sum + i) max sum)  //max(i) =  largest sum achievable from first i elements
        val min = s.scanLeft(0)((sum, i) =&gt; (sum + i) min sum)  //min(i) = smallest sum achievable from first i elements
    
        val dp: Memo[(Int, Int), Boolean] = Memo {         // dp(i,x) = can we achieve x using the first i elements?
          case (_, 0) =&gt; true        // 0 can always be achieved using empty set
          case (0, _) =&gt; false       // if empty set, non-zero cannot be achieved
          case (i, x) if min(i) &lt;= x &amp;&amp; x &lt;= max(i) =&gt; dp(i-1, x - s(i-1)) || dp(i-1, x)  // try with/without s(i-1)
          case _ =&gt; false            // outside range otherwise
        }
    
        dp(s.length, t)
      }

Is there a generic way to memoize in Scala?

Given an Option, what is the idiomatic way to get its value or throw an exception trying?

    def foo() : String = {
      val x : Option[String] = ...
      x.getOrException()
    }

Get Option value or throw an exception

there is an aspect of futures that I do not exactly understand from the official tutorial ref. [http://docs.scala-lang.org/overviews/core/futures.html][1]

Do futures in scala have a built in time-out mechanism of some kind? Let&#39;s say the example below was a 5 gigabyte text file... does the implied scope of &quot;Implicits.global&quot; eventually cause onFailure to fire in a non-blocking way or can that be defined? And without a default time-out of some kind, wouldn&#39;t that imply it&#39;s possible neither success nor failure would ever fire? 


    import scala.concurrent._
    import ExecutionContext.Implicits.global
    
    val firstOccurence: Future[Int] = future {
      val source = scala.io.Source.fromFile(&quot;myText.txt&quot;)
      source.toSeq.indexOfSlice(&quot;myKeyword&quot;)
    }
    firstOccurence onSuccess {
      case idx =&gt; println(&quot;The keyword first appears at position: &quot; + idx)
    }
    firstOccurence onFailure {
      case t =&gt; println(&quot;Could not process file: &quot; + t.getMessage)
    }


  [1]: http://docs.scala-lang.org/overviews/core/futures.html

Scala Futures - built in timeout?

I am new to Scala started learning the language for fun and I am still trying to get my head around it. My understanding of Scala traits is that they are like java interfaces except that some methods can have an implementation.

Java 8 is adding interfaces that can have default methods where an implementation can be provided. 

What are the similarities and differences between Java 8 interfaces and Scala traits?

Content Type	Original Author	Original Content on Stackoverflow
Question	Loic	View Question on Stackoverflow
Solution 1 - Scala	drexin	View Answer on Stackoverflow

How to get an Option from index in Collection in Scala?

Scala Problem Overview

Scala Solutions

Solution 1 - Scala

Twitter bootstrap collapse: change display of toggle button

How to insert a large block of HTML in JavaScript?

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