;/2

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The predicate ;/2 is defined as an infix operator. It is used to express disjunctive subgoals. For example member/2 can be rewritten as:



member(X
[HT]):-



(



X=H



;



member(X
T)



).

The semantics of ;/2 are roughly equivalent to logical or. Best to avoid its use.

The predicate definition



a:- b ; c.

is better written as:

a:- b. a:- c.

If you do use this construct then avoid nesting it deeply as this makes code very hard to read and understand.

Paul Brna
Mon May 24 20:14:48 BST 1999