support fpr conj etc

library/clauses.yap

@@ -0,0 +1,71 @@
+
+:- module(clauses,
+          [list2conj/2,
+           conj2list/2,
+	   clauselength/2]).
+
+%%! @{
+
+/**
+  @file clauses.yap
+  @defgroup clauses Clause Manipulation
+  @ingroup library
+
+  This library supports a number of useful utilities that come up over and
+  over again when manipulating Prolog programs. This will include
+  operations and conversion to other structures.
+
+  @author Vitor Santos Costa
+*/
+
+/** conj2list( +Conj, -List) is det
+  Generate a list from a conjunction of literals.
+
+  It is often easier to apply operations on lists than on clauses
+*/
+conj2list( Conj, List ) :-
+	conj2list( Conj, List, [] ).
+
+
+conj2list( C ) -->
+	{ var(C) },
+	!,
+	[C].
+conj2list( true )  --> !.
+conj2list( (C1, C2) ) -->
+	!,
+	conj2list( C1 ),
+	conj2list( C2 ).
+conj2list( C ) -->
+        [C].
+
+/** conj2list( +List, -Conj) is det
+  Generate a conjunction from a list of literals.
+
+  Notice that this relies on indexing within the list to avoid creating
+  choice-points.
+*/
+list2conj([], true).
+list2conj([Last], Last).
+list2conj([Head,Next|Tail], (Head,Goals)) :-
+	list2conj([Next|Tail], Goals).
+
+/** clauselength( +Clause, -Length) is det
+  Count the number of literals in a clause (head counts as one).
+
+  Notice that this is 1+length(conj2list), as we ignore  disjunctions.
+*/
+clauselength( (_Head :- Conj), Length ) :-
+	clauselength( Conj, Length, 1 ).
+
+
+clauselength( C, I1, I ) :-
+	{ var(C) },
+	!,
+	I1 is I+1.
+clauselength( (C1, C2), I2, I ) :- !,
+	clauselength( C1, I1, I ),
+	clauselength( C2, I2, I1 ).
+clauselength( _C, I1, I ) :-
+        I1 is I+1.
+