Constructing Data Structures

  $\mbox{$\bullet$}$

Functors can be thought of as representing non-interpreted functions

  $\mbox{$\bullet$}$

This function is applied (but not interpreted) to its arguments

  $\mbox{$\bullet$}$

The main application of functors is as data structure constructors

  $\mbox{$\bullet$}$

Sample program, step by step

  $\mbox{$\bullet$}$

We have a small database of people who are friends:

friends(peter, mark).
friends(anna, marcia).
friends(anna, luca).

?- friends(anna, X).
X = marcia ;
X = luca

?- friends(X, anna).
no

  $\mbox{$\bullet$}$

No friends?