Evaluation Strategies and Termination

Call-By-Value termination always implies Call-By-Name termination. However, the converse is not true. For example, given a function {def foo(x: Int, y: Int) = x} and we call foo(1,loop) where loop does not terminate,

1. In CBV, we need to evaluate loop which does not terminate so this does not terminate
2. In CBN, we only need the first argument which it will readily return

Scala normally uses Call-By-Value because it is usually exponentially faster to compute. However, you can make a function use CBN by adding a => such as: {def constOne(x: Int, y: => Int) = 1}

If we call const(1+2, loop) we get const(3,loop) which evaluates to 1 since the parameter loop is CBN. On the other hand, if we call const(loop, 1+2), we will get an infinite cycle!