For our simple game, we’ve defined global variables and functions. However, in most cases you’ll want to limit your definitions to a single function or a block of code. These are called local variables and functions.

To define a local variable, use the command let. A let command has the following structure:

 (let (variable declarations)
   ...body...)

The first thing inside the let command is a list of variable declarations . This is where we can declare one or more local variables. Then, in the body of the command (and only within this body), we can use these variables . Here is an example of the let command:

 > (let ((a 5)
         (b 6))
     (+ a b))
  11

In this example, we’ve declared the values 5 and 6 for the variables a and b , respectively. These are our variable declarations. Then, in the body of the let command, we added them together , resulting in the displayed value of 11.

When using a let expression, you must surround the entire list of declared variables with parentheses. Also, you must surround each pair of variable names and initial variables with another set of parentheses.