May 2018
Beginner
252 pages
6h 19m
English
The data word from the previous section is not only a name for the series—it is also a pointer to where we are in the series at a particular moment. You could call that position the current index, which is given by the index? function. Right after the series is created, we have index? data ;== 1 . Here is a diagram so you can quickly see what is going on:

When the current index is 1, we are also at the head of the series:
;-- see Chapter05/navigating-and-looping.red:head? data ;== true
The head data ...