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Chapter 1: Introduction
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1.3 Using Lpp
Using the Lpp library is easy. First you need to include in your C++ file
#include <Lpp.hh>
In some fussy cases you may want to include LppPure.hh here instead of Lpp.h, but
Lpp.hh is always safe to use, See Section 1.5 [Pure Lisp Include File], page 10.
Second, you need to link the library libLpp.a with the compile of your C++ program.
libLpp.a gets installed on your system when Lpp is installed, See Section 1.2 [Installing
Lpp], page 4. For example on Linux if you had installed Lpp under /usr/local and then
wrote a C++ program that used Lpp called main.cc then the following would first compile
a program main.cc and then make an executable called pgm
c++ -I/usr/local/include -c main.cc
c++ -o pgm main.o /usr/local/lib/lpp/libLpp.a
Then after that, if you are familiar with Common Lisp, you will find that writing programs using Lpp is similar to writing programs in Common Lisp. A big advantage is that
you can mix quite freely the static style of C++ with the dynamic style of Lisp without having to think about it too much. In the next section we give a simple example to illustrate
this.
1.4 A Simple Data Base Example
In this example we create a class that implements a simple data base. We then create an
instance of the data base and populate it with some entities, namely some people. And
finally we generate a report on the people of a family that we used to populate the data
base to show the relational aspect of the data base.
Lpp is useful here since we want entities to be any kind of object and hence dynamically
bound objects will index the data base. In the example we use Lpp symbols to designate
entities. We set relations in the data base with a typical entity attribute value tuple. So
the data base access member functions are as follows
• getSize() = Returns the total number of entities in the data base
• addEntity(entity) = Add entity (any Lpp object) to the data base
• setValue(entity, attribute, value) = Add a relation for entity
• getValue(entity, attribute) = Returns the attribute value for entity
Here is the implementation of the data base class