“Once the word “square” has been defined, it becomes part of the computer’s vocabulary and can then be used to define other words. For example, TO WINDOW SQUARE SQUARE SQUARE SQUARE END Each square will be drawn in a different place, because the procedure for drawing the square leaves the turtle rotated 90 degrees. In computer terms, SQUARE is a subroutine of the program WINDOW, which calls it. The subroutine SQUARE, in turn, is defined using the primitives FORWARD and RIGHT. User-defined words in Logo can take parameters, too. For instance, a child can specify various sizes of square by specifying what parameter determines the length of each side.”