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3.1 The Read-Eval-Print Loop

When you first start up Scheme from the command line, you will be typing at a program called the Read-Eval-Print Loop (abbreviated REPL). It displays a prompt at the left hand side of the screen whenever it is waiting for input. You then type an expression (terminating it with <RET>). Scheme evaluates the expression, prints the result, and gives you another prompt.