This program consists of three directives:
$use StdIO; // Import i/o functions from the module StdIO
$func Main = e; // Declare the format of the main function:
// empty as input, anything as output.
Main // Define the main function
= <PrintLn "Hello!">; // Print a line
The first directive
$use StdIO;
states that the program is going
to use library input/output functions, which are to be imported from the module
StdIO. The second directive declares the format of the function Main: what
is what it can accept as input, and what it will produce as output. The third directive is the
definition of the function Main, and, by convention, the execution of a
Refal Plus program always begins by evaluating the call to the function
Main.
The argument of the function Main must be empty. In the above program, the
function Main calls the library function PrintLn with
the argument "Hello!", thereby causing the character string
Hello!
followed by the character "new line", to be sent to the
standard output device. Then the execution of the program terminates.