Introduce MeetLink as non Set-using version of GetLink

This partly resolves issues opencog#2530 and opencog#1502

opencog/atoms/atom_types/atom_types.script

@@ -402,7 +402,8 @@ SATISFYING_LINK <- PATTERN_LINK
 // Both return SetLinks holding the results.
 // QueryLink is identical to BindLink, except it returns a LinkValue
 // holding the result, instead of a SetLink. (Less atomspace pollution).
-GET_LINK <- SATISFYING_LINK        // Finds all groundings, returns them
+MEET_LINK <- SATISFYING_LINK       // Finds all groundings, returns them
+GET_LINK <- MEET_LINK              // Finds all groundings, returns them
 QUERY_LINK <- SATISFYING_LINK      // Finds all groundings, substitutes.
 BIND_LINK <- QUERY_LINK            // Finds all groundings, substitutes.
 

opencog/atoms/pattern/CMakeLists.txt

@@ -6,6 +6,7 @@ ADD_LIBRARY (lambda
 	BindLink.cc
 	DualLink.cc
 	GetLink.cc
+	MeetLink.cc
 	PatternLink.cc
 	PatternTerm.cc
 	PatternUtils.cc
@@ -32,6 +33,7 @@ INSTALL (FILES
 	BindLink.h
 	DualLink.h
 	GetLink.h
+	MeetLink.h
 	PatternLink.h
 	Pattern.h
 	PatternTerm.h

opencog/atoms/pattern/GetLink.cc

@@ -40,26 +40,16 @@ void GetLink::init(void)
 }
 
 GetLink::GetLink(const HandleSeq&& hseq, Type t)
-	: PatternLink(std::move(hseq), t)
+	: MeetLink(std::move(hseq), t)
 {
 	init();
 }
 
 /* ================================================================= */
 
-QueueValuePtr GetLink::do_execute(AtomSpace* as, bool silent)
-{
-	if (nullptr == as) as = _atom_space;
-
-	SatisfyingSet sater(as);
-	this->satisfy(sater);
-
-	return sater.get_result_queue();
-}
-
 ValuePtr GetLink::execute(AtomSpace* as, bool silent)
 {
-	QueueValuePtr qv(do_execute(as, silent));
+	QueueValuePtr qv(MeetLink::do_execute(as, silent));
 	OC_ASSERT(qv->is_closed(), "Unexpected queue state!");
 	HandleSeq hs(qv->to_handle_seq());
 

opencog/atoms/pattern/GetLink.h

@@ -22,26 +22,24 @@
 #ifndef _OPENCOG_GET_LINK_H
 #define _OPENCOG_GET_LINK_H
 
-#include <opencog/atoms/pattern/PatternLink.h>
+#include <opencog/atoms/pattern/MeetLink.h>
 
 namespace opencog
 {
 /** \addtogroup grp_atomspace
  *  @{
  */
-class GetLink : public PatternLink
+class GetLink : public MeetLink
 {
 protected:
 	void init(void);
-	virtual QueueValuePtr do_execute(AtomSpace*, bool silent);
 
 public:
 	GetLink(const HandleSeq&&, Type=GET_LINK);
 
 	GetLink(const GetLink&) = delete;
 	GetLink operator=(const GetLink&) = delete;
 
-	virtual bool is_executable() const { return true; }
 	virtual ValuePtr execute(AtomSpace*, bool silent=false);
 
 	static Handle factory(const Handle&);

opencog/atoms/pattern/MeetLink.cc

@@ -0,0 +1,67 @@
+/*
+ * MeetLink.cc
+ *
+ * Copyright (C) 2019 Linas Vepstas
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License v3 as
+ * published by the Free Software Foundation and including the
+ * exceptions at http://opencog.org/wiki/Licenses
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License along with this program; if not, write to:
+ * Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <opencog/util/oc_assert.h>
+#include <opencog/atoms/atom_types/NameServer.h>
+#include <opencog/atoms/core/UnorderedLink.h>
+#include <opencog/query/Satisfier.h>
+
+#include "MeetLink.h"
+
+using namespace opencog;
+
+void MeetLink::init(void)
+{
+	Type t = get_type();
+	if (not nameserver().isA(t, MEET_LINK))
+	{
+		const std::string& tname = nameserver().getTypeName(t);
+		throw InvalidParamException(TRACE_INFO,
+			"Expecting a MeetLink, got %s", tname.c_str());
+	}
+}
+
+MeetLink::MeetLink(const HandleSeq&& hseq, Type t)
+	: PatternLink(std::move(hseq), t)
+{
+	init();
+}
+
+/* ================================================================= */
+
+QueueValuePtr MeetLink::do_execute(AtomSpace* as, bool silent)
+{
+	if (nullptr == as) as = _atom_space;
+
+	SatisfyingSet sater(as);
+	this->satisfy(sater);
+
+	return sater.get_result_queue();
+}
+
+ValuePtr MeetLink::execute(AtomSpace* as, bool silent)
+{
+	return do_execute(as, silent);
+}
+
+DEFINE_LINK_FACTORY(MeetLink, MEET_LINK)
+
+/* ===================== END OF FILE ===================== */

opencog/atoms/pattern/MeetLink.h

@@ -0,0 +1,61 @@
+/*
+ * opencog/atoms/pattern/MeetLink.h
+ *
+ * Copyright (C) 2019 Linas Vepstas
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License v3 as
+ * published by the Free Software Foundation and including the exceptions
+ * at http://opencog.org/wiki/Licenses
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program; if not, write to:
+ * Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+#ifndef _OPENCOG_MEET_LINK_H
+#define _OPENCOG_MEET_LINK_H
+
+#include <opencog/atoms/pattern/PatternLink.h>
+
+namespace opencog
+{
+/** \addtogroup grp_atomspace
+ *  @{
+ */
+class MeetLink : public PatternLink
+{
+protected:
+	void init(void);
+	virtual QueueValuePtr do_execute(AtomSpace*, bool silent);
+
+public:
+	MeetLink(const HandleSeq&&, Type=MEET_LINK);
+
+	MeetLink(const MeetLink&) = delete;
+	MeetLink operator=(const MeetLink&) = delete;
+
+	virtual bool is_executable() const { return true; }
+	virtual ValuePtr execute(AtomSpace*, bool silent=false);
+
+	static Handle factory(const Handle&);
+};
+
+typedef std::shared_ptr<MeetLink> MeetLinkPtr;
+static inline MeetLinkPtr MeetLinkCast(const Handle& h)
+	{ AtomPtr a(h); return std::dynamic_pointer_cast<MeetLink>(a); }
+static inline MeetLinkPtr MeetLinkCast(AtomPtr a)
+	{ return std::dynamic_pointer_cast<MeetLink>(a); }
+
+#define createMeetLink std::make_shared<MeetLink>
+
+/** @}*/
+}
+
+#endif // _OPENCOG_MEET_LINK_H