A program is merely a set of one or more Vision requests. All the programs you have seen so far have asked Vision to perform a single request. There are situations where you would like to perform a set of operations, one after another. Vision provides a simple mechanism for accomplishing this. Each expression is executed in sequence.
Vision automatically sends the print message to the result of the last expression.
If you terminate the last expression with a semi-colon, the automatic printing is suppressed. A block is a special form of program that represents a deferred sequence of steps. Blocks always return the value of the last statement executed. Blocks are often used as parameters to other messages. Otherwise, the program supplied by the second block is executed.