Basic Genie Samples

Hello World

A very simple Hello World program:

init
    print ("hello, world\n")

Compile and Run

$ valac hello.gs
$ ./hello

If the binary should have a different name:

$ valac hello.gs -o greeting
$ ./greeting

Reading User Input

init
        stdout.printf ("Please enter your name: ")
        name : string = stdin.read_line ()
        if name is not null
                stdout.printf ("Hello, %s!\n", name)

Genie provides the objects stdin (standard input), stdout (standard output) and stderr (standard error) for the three standard streams. The printf method takes a format string and a variable number of arguments as parameters.

Mathematics

Math functions are inside the Math namespace.

init

        stdout.printf ("Please enter the radius of a circle: ")
        radius : double = double.parse (stdin.read_line ())
        stdout.printf ("Circumference: %g\n", 2 * Math.PI * radius)

        stdout.printf ("sin(pi/2) = %g\n", Math.sin (Math.PI / 2))

        // Random numbers

        stdout.printf ("Today's lottery results:")

        for var i = 0 to 6 
                stdout.printf (" %d", Random.int_range (1, 49))

        stdout.printf ("\n")
        stdout.printf ("Random number between 0 and 1: %g\n", Random.next_double ())

Command-Line Arguments and Exit Code

init

        // Output the number of arguments
        stdout.printf ("%d command line argument(s):\n", args.length)

        // Enumerate all command line arguments
        for s in args 
                stdout.printf ("%s\n", s)

The first command line argument (args[0]) is always the invocation of the program itself.

Reading and Writing Text File Content

This is very basic text file handling. For advanced I/O you should use GIO's powerful stream classes.

init
        try
                filename : string = "data.txt"

                // Writing
                content : string = "hello, world"
                FileUtils.set_contents (filename, content)

                // Reading
                read : string
                FileUtils.get_contents (filename, out read)

                stdout.printf ("The content of file '%s' is:\n%s\n", filename, read)
        except e : FileError
                stderr.printf ("%s\n", e.message);

Spawning Processes

init
        try 
                // Non-blocking
                Process.spawn_command_line_async ("ls")

                // Blocking (waits for the process to finish)
                Process.spawn_command_line_sync ("ls")

                // Blocking with output
                standard_output : string
                standard_error : string
                exit_status : int
                Process.spawn_command_line_sync (
                        "ls", out standard_output, out standard_error, out exit_status)
        except e : SpawnError 
                stderr.printf ("%s\n", e.message)

First Class

/* class derived from GObject */
class BasicSample : Object 

        /* public instance method */
        def run () 
                stdout.printf ("Hello World\n")

/* application entry point */
init
        // instantiate this class, assigning the instance to
        // a type-inferred variable
        var sample = new BasicSample ()
        // call the run method
        sample.run ()
        // return from this main method

The entry point may as well be inside the class, if you prefer it this way:

class BasicSample : Object 

        def run () 
                stdout.printf ("Hello World\n")

        def static main () 
                var sample = new BasicSample ();
                sample.run ();

In this case main must be declared static.

More Genie Examples