What type of exception is thrown when a precondition is violated?

In scala what is precondition?

What would you change in this code to make it execute in parallel?

What is a free variable?

What's the best way to execute code in the background in a separate thread?

What value does this code return? x= List(1,2,4); x(1)?

`Nil` is generally the same as:

Does Scala support tail-call recursion?

A valid description of a covariant type parameter would be:

Describe class AnyRef

In the expression: List(1,2,3).foldLeft(x){case (a,b) => a+b} `x` is: