TOM is an object oriented programming language. The following example shows the famous `hello world' program, this time written in TOM.
1 implementation class HelloWorld: stdio
2
3 int
4 main Array arguments
5 {
6 [[out print "Hello, world!"] nl];
7
8 = 0;
9 }
10
11 end;
12
13 implementation instance HelloWorld end;
In line 1, a class is defined with the name HelloWorld. It
inherits from stdio, implying that anything defined by the
stdio class is directly available.
Line 2 is empty. That's ok, as empty lines have no significance.
From line 3 to 9, a method is defined. This method is named
main; it accepts one argument, named arguments, the type
of which is Array; it returns an int.
The main method, when implemented by a class, is special as it is
the method invoked when the program is started. The arguments
argument is an array of strings holding the command line arguments to
the program. main returns an int which will be the exit
value of the program.
In line 6, two methods are invoked. Invoking a method is the same as
sending a message. The first invocation send a message print to
the object known as out. out is a variable inherited
from stdio; it is the `standard output' stream of the program,
known as stdout in C. The print message has one argument,
a string containing `Hello, world!'.
By convention, every print method implemented by a stream returns
the receiver, so that the invocation itself can be used as the receiver
of another message to the stream. In this case, the argument-less
message nl is sent. This causes a new line to be output to the
standard output stream, and that stream to be flushed to make sure any
buffered contents will be displayed on the user's terminal. nl
also returns the receiver, but that value is ignored.
In line 8, the assignment of 0 with an empty left-hand-side sets
the value to be returned from this method. It returns 0, a value
which indicates success. Note that this form of the return value
assignment does not actually cause an immediate return from this method
(it would if the = were replaced by return).
By the end in line 11, the definition of the HelloWorld
class is finished. In line 13, the instances of the HelloWorld
class are defined. Since we never allocate HelloWorld instances,
this definition is rather empty.
So much for an easy introduction. The rest of this document will be more of a reference manual, with not that many elaborate examples.
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