## Programming the chess board in Logo

Two approaches to the same problem of making a chess board pattern in Logo. Breaking down a problem into smaller, easier-to-solve problems is a key skill of the computer programmer. When presented with the chess board task, a programmer wouldn’t think about how to solve the whole problem but she would immediately identify small parts of the solution that would be useful to have solved first. For instance, it would be useful to have a procedure that makes a square so she would code that first. Once this procedure is written, it’s easy to create a procedure that makes a whole row of squares. And once the row procedure is created, making a whole chess board is really quite trivial.

Here is an elegant solution:

to board :size repeat 8 [row :size fd :size] end

to row :size repeat 8 [square :size rt 90 fd :size lt 90] lt 90 fd 8*:size rt 90 end

to square :size repeat 4 [fd :size rt 90] end

Conversely, it is possible to see the task of making the chess board as a linear sequence of loads and loads of instruction. That approach results in disgusting code like this:

to disaster fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 fd 20 rt 90 rt 90 fd 20 lt 90 lt 90 fd 160 rt 90 fd 20 end