Hello World
-----------
The first example program, hello.swift, outputs a hello world message
into a file called hello.txt.

.hello.swift
************
 
----
include::../../examples/tutorial/hello.swift[]
----
************

To run hello.swift, change directories to the location of the script
and run the swift command as follows.

TIP: Make sure the bin directory of your swift installation is in your PATH.
----
$ cd examples/tutorial
$ swift hello.swift
Swift svn swift-r3334 (swift modified locally) cog-r2752

RunID: 20100526-1925-8zjupq1b
Progress:
Final status:  Finished successfully:1
$ cat hello.txt
Hello, world!
----

The basic structure of this program is a type definition, an
application procedure definition, a variable definition and then a
call to the procedure.
 
First we define a new type, called messagefile. In this example, we will
use this messagefile type for our output message.

----
sys::[sed -n '1p' ../../examples/tutorial/hello.swift]
----

All data in SwiftScript must be typed, whether it is stored in memory or
on disk. This example defines a very simple type. Later on we will see
more complex type examples.
 
----
sys::[sed -n '3,5p' ../../examples/tutorial/hello.swift]
----

Next we define a procedure called greeting. This procedure will write
out the "hello world" message to a file. To achieve this, it executes 
the unix utility 'echo' with a parameter "Hello, world!" and directs 
the standard output into the output file.

The actual file to use is specified by the return parameter, t.
-----
sys::[sed -n '7p' ../../examples/tutorial/hello.swift]
-----
Here we define a variable called outfile. The type of this variable is
messagefile, and we specify that the contents of this variable will be
stored on disk in a file called hello.txt

-----
sys::[sed -n '3,5p' ../../examples/tutorial/hello.swift]
-----
Now we call the greeting procedure, with its output going to the outfile
variable and therefore to hello.txt on disk.

Over the following exercises, we'll extend this simple hello world
program to demonstrate various features of Swift.