====== If then ======
{{tag>statements}}
===== Description =====
If-then-else statement

**Source**:  The Art of Prolog
===== Download =====
Program source code: {{if_then.pl}}
===== Listing =====
<code prolog>
/*
   if_then_else(P,Q,R) :- Either P and Q, or not P and R.
*/
     if_then_else(P,Q,R) :- P, !, Q.
     if_then_else(P,Q,R) :- R.

%   Program 11.10    If-then-else statement
</code>
===== Comments =====