A++ with few extensions

In order to be able to display computational results to the screen it is necessary to introduce a few primitives into A++. It will also be very helpful to introduce symbolic constants and strings into A++. These extension are briefly described below:

• vmzero a reference to the number ``0'' in the machine.
  
  
• vmtrue a reference to the boolean value 'true' in the interpreter.
  
  
• vmfalse a reference to the boolean value 'false' in the interpreter.
  
  
• double-quoted-string This abstraction introduces strings into A++. They are needed in the context of the ``load'' primitive allowing to load A++ - code from a file.
  
  
• single-quoted-string This abstraction introduces symbolic constants into A++. They are convenient in the context of object oriented programming, when sending messages to objects..
  
  
• incr This primitive is used to increment a number in the virtual machine by one.
  
  
• print This primitive displays a number or a boolean value on the screen.
  
  
• load Primitive allowing to load A++ - code from a file.
  
  
• equalx Primitive allowing to compare data items other than Church Numerals (numbers directly derived from ARS).
  
  
• quit Function to terminate execution of program.
  
  

These primitive abstractions are used in the following

A++ - lambda abstractions:

• ndisp! displays a numerical value,
  
  
• bdisp! displays a boolean value,
  
  
• ldisp! displays a list.
  
  

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