Introduction to XMF

int fib(int x) {
   return x <= 1 ? 1 : fib(x - 1) + fib(x - 2);
}
 
(define (fib x)
  (if (<= 1)
    x
    (+ (fib (- x 1)) (fib (- x 2))))
 
function fib(int x) : int
begin
  if x <= 1 then
  begin
    result := 1;
  end
  else
  begin
    result := fib(x - 1) + fib(x - 2);
  end
end
 
define fib(x) {
  x 1 <= [1] [x 1 - fib x 2 - fib +] if
}

@Model Quiz
  // The Quiz model describes an interactive application
  // for a TV quiz. Viewers are presented with a sequence
  // of questions and get a final score...
  score : Integer;
  // Screen definitions
 
  screen START()
    vertical
      text Welcome to the Quiz. Click the button to Start end
      button Start
        go Question1()
      end
    end
  end
 
  screen Question1()
    vertical
      text What is the capital of England? end
      options Choice
        option London; 
        option Paris;
        option Madrid;
      end
 
    horizontal
      button Next
        // Next action continues...
      end
      button Quit
       go Quit()
      end
    end
  end
end

if self.timeForC()
then
 // Let's drop into C...
 @C
     // some C stuff....
	
     int x; 
     x = 10; 
     while(x > 0) { 
       @x.println(); x = x - 1;
     }
 
 end
 // Back out to XCore	
else 
  self.noCforMe()
end

if self.timeForC()
then
 // Let's drop into C...
 @C
     // some C stuff....
	
     int x; 
     x = 10;
 
     // Back out to XCore
 
     @For e in x
     do
       format(stdout,"~S~%",Seq{x})
     end
 end
 // Back out to XCore	
else 
  self.noCforMe()
end

  @Class DataBaseClass extends Class

    // This is a meta-class that implements a MOP
    // for connecting to a database. The instances
    // of a DataBaseClass are effectively rows in the
    // table...
 
    // Any database class has a reference to the external
    // database table...
    
    @Attribute table : DataBaseTable end
 
    // The class knows about the primary key that is used
    // to reference the individual objects in the table...
 
    @Attribute primaryKey : String end

    @Operation getInstanceSlot(object:Object,name:String)
 
      // This operation implements '.' for an instance of
      // a database class. The object proxies the row in the
      // table via the primary key value...
 
      table.selectRow(object,primaryKey,name)
    end

    @Operation new(Seq{key})
 
      // When an instance of a database class is created
      // this operation creates a new row...
 
      table.createRow(self,key)
    end

    // More MOP for the := operator etc...

  end
 

  // Create a database table...
 
  @Class Personnel metaclass DataBaseClass end
 
  // Set the table and primary key..
 
  Personnel.table := DataBaseTable("jdbc:mysql://localhost/Personnel");

  // Creating an instance of the Personnel class will create a row...
 
  o := Personnel("Fred Brown");

  // Referencing a slot will use the getInstanceSlot operation...
 
  o.name

[1] XMF> Date := xmf.javaClass("java.util.Date");

<Root>

[1] XMF> Date();

Tue Dec 11 12:29:31 GMT 2007

[1] XMF>

  @Class Personnel metaclass JavaClass

    // This is an XMF class that 'wraps' behaviour around the
    // Java class. Instances of this class can be created in
    // XMF (in which case an instance of the Java class is
    // created) or can be passed from a Java application...

    JavaDescriptor("mypackage.Personnel")

    @Operation reset()

     // This is a new behaviour added to the Java class
     // that is defined in terms of the methods provided by 
     // the Java class. When the Java methods are called, XMF
     // deals with translating the XMF values to Java and 
     // vice versa...

     self.setName("");
     self.setAge(0);
     self.setAddress("")
    end
  end

  @Operation addUp(t:Tree):Integer
    @Case t of
      Branch(tree1,tree2) do
        addUp(tree1) + addUp(tree2)
      end
      Leaf(n) do
        n
      end
    end
  end

let v = Vector(1)
in
  format(stdout,"v before update : ~S~%",Seq{v});
  @Undoable v.put(0,"Frank") end;
  format(stdout,"v after update  : ~S~%",Seq{v});
  xmf.undoEngine().undo();
  format(stdout,"v after undo    : ~S~%",Seq{v});
  xmf.undoEngine().redo();
  format(stdout,"v after redo    : ~S~%",Seq{v})
end;

v before update : Vector{null}
v after update  : Vector{Frank}
v after undo    : Vector{null}
v after redo    : Vector{Frank}
0:0:0:16  ms ]
true
[1] XMF>