PPT Slide

Clause provides another way of selecting Horn clauses.

Clause( X, Y ) succeeds if it can match X and Y to the head and body of an existing clause in the database.

X must be instantiated enough so that the main predicate is known. Only works for dynamically asserted clauses!!

Example

list1( X ) :- clause( X, Y ), output_clause( X, Y ), write( ' · ' ), nl, fail.

list1( X ).

output_clause( X, true ) :- !, write( X ).

output_clause( X, Y ) :- write( ( X :- Y ) ).

Note that for facts, the tail is true.

Ex. assert( q ( a, b ) ).

list1( q ( V1, V2 ) ) .