I'm using Scala 2.9.2, and would like to construct a list based on some conditions.

Consider the following, where cond is some function taking a predicate p and a value of type T (in this case t3):

t1 :: t2 :: cond( p, t3 ) :: t4

The behaviour I want is as follows. If p is true, this should give:

List[T]( t1, t2, t3, t4 )

If p evaluates to false, this should give:

List[T]( t1, t2, t4 )

I'm probably thinking about this completely the wrong way, but I'm struggling to come up with an elegant solution. I could involve Options everywhere and then filter, but that's makes the code rather harder to read:

def cond[T]( p : => Boolean, v : T ) : Option[T] =
{
    p match
    {
        case true => Some( v )
        case false => None
    }
}

This allows the following:

scala> ( Some( 1 ) :: Some( 2 ) :: cond( true, 3 ) :: Some( 4 ) :: Nil ).flatten
res4: List[Int] = List(1, 2, 3, 4)

scala> ( Some( 1 ) :: Some( 2 ) :: cond( false, 3 ) :: Some( 4 ) :: Nil ).flatten
res5: List[Int] = List(1, 2, 4)

However, it's not the most elegant solution, as it requires the user to wrap all of the their non-conditional elements in Some( ) and also to remember to do the flatten at the end. Can anyone think of a more elegant solution?

scala collections
Edit
Report