When you use Enum.take_while/2 , it processes the entire enumerable immediately and produces a result. (greedy)
Stream.take_while/2 by itself doesn’t actually compute anything. If it is the final step in a chain of transformations, the enumerable still needs to be explicitly evaluated to get the actual list. Stream functions are lazy in that they only occurs when you force the stream to be evaluated using Stream.run/1 or an Enum functions.
The thing that really helped me understand this a lot better is looking at the difference in how a List implement the Enumberable protocol’s ‘reduce/3’ function. vs. how Stream does.
