Whileloop : Defining Iteration Conditions

Whileloop allows a loop to go on while a condition is fulfilled .

It has only one default input : "expression", which defines a condition. This condition is expressed by a predicate¹ that is connected to the input of whileloop.

We have added a list that contains numbers and letters. We want to stop the enumeration of the list if we get something else than a number.

1. The list is enumerated by listloop. Each item returned by listloop is sent to the predicate numberp.

2. Numberp tests if the item is a number, and returns "t" or "nil" .

3. The result of the predicate is returned to whileloop. As long as whileloop gets "t", the loop goes on.

   When numberp returns "nil", whileloop stops the loop, and finally returns "done".

4. At each step of the loop, the results returned by listloop and numberp are gathered in a list, and EachTime prints the list.