Parsing, on a projected table

Adding Machine Table

A row of number cards hides a list of lists: 0 ends a group and 0 0 ends the input. The parser page draws that structure onto the cards. The summer page adds each group. Move the cards and the projection updates.

Drag cards, or focus one and use the arrow keys. Click a page to lift it off the table.

table · projector on

group separator 0 stop (0 0) needs a 0

Things to try

Drag a 0 between the 3 and the 4. The group splits in two, with a sum for each half.
Drag a separator 0 out of the row. The groups on either side merge.
Pull one card of the 0 0 pair away. The stop disappears and 7 8 waits for a closing 0.
Lift the summer page. The boxes stay and the sums go: the structure came from the parser.
Lift the parser page too. What's left is paper with numbers on it.