Generic comparison based lattice node

Author: mikera

convex-core/src/main/java/convex/core/data/prim/AInteger.java

@@ -89,6 +89,7 @@ public static AInteger parse(Object o) {
 	 * @return Number of bytes
 	 */
 	public abstract int byteLength();
+	
 
 	@Override
 	public ANumeric add(ANumeric b) {

convex-core/src/main/java/convex/core/lattice/CompareNode.java

@@ -0,0 +1,43 @@
+package convex.core.lattice;
+
+import java.util.Comparator;
+
+import convex.core.data.ACell;
+
+/**
+ * Lattice node implementing a comparison function.
+ * 
+ * Suitable for lattice values where "greater" values replace previous ones, 
+ * e.g. taking a value with a more recent timestamp 
+ * 
+ * @param <V> Type of lattice values
+ */
+public class CompareNode<V extends ACell> extends ALattice<V> {
+
+	private Comparator<V> comparator;
+
+	private CompareNode(Comparator<V> comparator) {
+		this.comparator = comparator;
+	}
+	
+	public static <V extends ACell> CompareNode<V> create(Comparator<V> comparator) {
+		return new CompareNode<>(comparator);
+	}
+	
+	@Override
+	public V merge(V ownValue, V otherValue) {
+		if (otherValue==null) return ownValue;
+		if (ownValue==null) return otherValue;
+		
+		// retain own value if other value is lesser or equal
+		if (comparator.compare(ownValue, otherValue)>=0) return ownValue;
+		
+		return otherValue;
+	}
+
+	@Override
+	public V zero() {
+		return null;
+	}
+
+}

convex-core/src/main/java/convex/core/lattice/KeyedNode.java

@@ -57,6 +57,8 @@ public static KeyedNode create(Object... keysAndValues) {
 			ALattice<ACell> lattice=(ALattice<ACell>) lattices.get(i);
 			Keyword key=keys.get(i);
 
+			if (!otherValue.containsKey(key)) continue;
+			
 			ACell a=ownValue.get(key);
 			ACell b=otherValue.get(key);
 

convex-core/src/main/java/convex/core/lattice/MapNode.java

@@ -26,6 +26,7 @@ public static <K extends ACell,V extends ACell> MapNode<K,V> create(ALattice<V>
 	@Override
 	public AHashMap<K,V> merge(AHashMap<K, V> ownValue, AHashMap<K, V> otherValue) {
 		if (otherValue==null) return ownValue;
+		if (ownValue==null) return otherValue;
 		return ownValue.mergeDifferences(otherValue, mergeFunction);
 	}
 

convex-core/src/test/java/convex/core/lattice/LatticeTest.java

@@ -44,6 +44,7 @@ public class LatticeTest {
 
 		doLatticeTest(KeyedNode.create("foo",MaxNode.create(),"bar",SetNode.create()),Maps.of(Keywords.FOO,CVMLong.ONE), Maps.of(Keywords.BAR,Sets.of(1,2)));
 
+		doLatticeTest(CompareNode.create((AInteger a,AInteger b)->a.compareTo(b)),CVMLong.ONE, CVMLong.MAX_VALUE);
 	}
 
 
@@ -59,6 +60,11 @@ private <V extends ACell> void doLatticeTest(ALattice<V> lattice, V value, V val
 		// Merges with zero
 		assertEquals(value,lattice.merge(zero,value));
 		assertEquals(value,lattice.merge(value,zero));
+
+		// Null merge
+		assertEquals(value,lattice.merge(value,null));
+		assertEquals(value,lattice.merge(null,value));
+
 
 		assertEquals(value2,lattice.merge(zero,value2));
 		assertEquals(value2,lattice.merge(value2,zero));