Row

Row has no village-craft family origin — concrete objects don't have biographies — so Loop introduces it by demonstration, not story. He fills the rack: box 0 gets "apple", box 1 gets "bread", box 2 gets "milk". Then he points to box 2. "Here's the one thing that trips everyone at first: the numbering starts at zero. So the third box is index 2. It looks off by one until you see why — the index is really 'how far from the start,' and the first box is zero steps from the start." He reaches in by index and pulls milk straight out of box 2, then bread out of box 1. "No searching the whole rack, no walking past the others. You name the position, you get that value — instantly. That's the power an array buys you: direct access by index."

Loop demonstrates Row's moves with Bit, the little robot the learner programs. "Bit needs a shopping list, so we give Bit a Row." He loads the list and shows the operations, one at a time — reach by index (list[0] gets the first value, counting from 0); append (a new box appears at the next number); update (swap what's inside a box without moving the box); length (count the boxes to know how many there are); iterate (hand the boxes to a loop, one by one, in order). "An array doesn't decide anything," Loop says. "It doesn't think. It holds many values in order and lets you reach any of them by number. Reach by index, append, update, ask its length, or walk it. That is the entire job — and it's exactly enough."

Loop hands Row to Trek, the loop, so the kid can watch an array and a loop work together — the heart of most real programs. "Bit, walk the list." Trek takes box 0, then 1, then 2, handing each value to Bit; Bit reads apple, then bread, then milk, checking each off; when the boxes run out, the walk ends on its own — because the loop runs for each index up to the length, and the length is exactly where it stops. The kid programs Bit to append eggs to the end, then walk the whole list again. Bit reads all four, finishes the last one, and stops. Every item handled, in order, none missed, none read twice. "Array plus loop," Loop says. "That pairing is most of the programs you'll ever write."