(refs #7250) Refactoring CHR implementation

[simantics/platform.git] / bundles / org.simantics.scl.runtime / src / org / simantics / scl / runtime / chr / CHRPriority.java

diff --git a/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/chr/CHRPriority.java b/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/chr/CHRPriority.java
new file mode 100644 (file)
index 0000000..008830b
--- /dev/null
+++ b/bundles/org.simantics.scl.runtime/src/org/simantics/scl/runtime/chr/CHRPriority.java
@@ -0,0 +1,78 @@
+package org.simantics.scl.runtime.chr;
+
+/**
+ * This class implements a pairing heap of CHR priorities.
+ */
+public abstract class CHRPriority implements Comparable<CHRPriority> {
+    
+    public final int priority;
+    
+    // Pairing heap
+    private CHRPriority sibling;
+    private CHRPriority child;
+    
+    boolean inContext;
+    
+    public CHRPriority(int priority) {
+        this.priority = priority;
+    }
+    
+    /**
+     * This method assume that a and b are roots and their sibling field
+     * can be overridden. 
+     */
+    public static CHRPriority merge(CHRPriority a, CHRPriority b) {
+        if(a.priority <= b.priority) {
+            a.sibling = null;
+            b.sibling = a.child;
+            a.child = b;
+            return a;
+        }
+        else {
+            a.sibling = b.child;
+            b.sibling = null;
+            b.child = a;
+            return b;
+        }
+    }
+    
+    protected void ensureInContext(CHRContext context) {
+        if(!inContext) {
+            CHRPriority topPriority = context.topPriority;
+            if(topPriority == null)
+                context.topPriority = this;
+            else
+                context.topPriority = merge(topPriority, this);
+            inContext = true;
+        }
+    }
+    
+    private CHRPriority mergeSiblings() {
+        if(sibling == null)
+            return this;
+        CHRPriority nextSibling = sibling.sibling;
+        CHRPriority merged = merge(this, sibling);
+        if(nextSibling == null)
+            return merged;
+        else
+            return merge(merged, nextSibling.mergeSiblings());
+    }
+    
+    public CHRPriority nextPriority() {
+        if(child == null)
+            return null;
+        else {
+            CHRPriority result = child.mergeSiblings();
+            child = null;
+            return result;
+        }
+    }
+    
+    @Override
+    public int compareTo(CHRPriority o) {
+        return Double.compare(priority, o.priority);
+    }
+    
+    public abstract void activate(CHRContext context);
+    //public abstract CHRRuntimeRuleset getParent();
+}