From c7a398170fe3bc8b0a9c0014d8e8183e392eda83 Mon Sep 17 00:00:00 2001
From: Ben Culkin <scorpress@gmail.com>
Date: Mon, 14 Dec 2020 18:24:47 -0500
Subject: Implement NestList

NestList is a recursive list structure, inspired by the way lists work
in Rakudo (formerly Perl 6).
---
 src/main/java/bjc/esodata/FlatNestIterator.java | 103 ++++++++++++++++++++++++
 1 file changed, 103 insertions(+)
 create mode 100644 src/main/java/bjc/esodata/FlatNestIterator.java

(limited to 'src/main/java/bjc/esodata/FlatNestIterator.java')

diff --git a/src/main/java/bjc/esodata/FlatNestIterator.java b/src/main/java/bjc/esodata/FlatNestIterator.java
new file mode 100644
index 0000000..42981f5
--- /dev/null
+++ b/src/main/java/bjc/esodata/FlatNestIterator.java
@@ -0,0 +1,103 @@
+package bjc.esodata;
+
+import java.util.*;
+
+import bjc.data.*;
+
+final class FlatNestIterator<Element> implements ListIterator<Element>
+{
+	private Deque<ListIterator<Either<Element, NestList<Element>>>> iterators;
+	
+	public FlatNestIterator(ListIterator<Either<Element, NestList<Element>>> iterator)
+	{
+		this.iterators = new ArrayDeque<>();
+		this.iterators.add(iterator);
+	}
+
+	@Override
+	public boolean hasNext() {
+		boolean result = false;
+		do {
+			result = iterators.peek().hasNext();
+			
+			if (result == false) iterators.pop();
+		} while (result == false && iterators.isEmpty() == false);
+		
+		return result;
+	}
+
+	@Override
+	public Element next() {
+		Holder<Element> element = Holder.of(null);
+		do {
+			element = iterators.peek().next().extract((ele) -> {
+				return Holder.of(ele);
+			}, (lst) -> {
+				// Ignore empty sublists.
+				if (lst.size() != 0) iterators.push(lst.listIterator());
+				
+				return null;
+			});
+		} while (element == null && hasNext());
+
+		if (element == null) throw new NoSuchElementException();
+		
+		return element.getValue();
+	}
+
+	@Override
+	public boolean hasPrevious() {
+		boolean result = false;
+		do {
+			result = iterators.peek().hasPrevious();
+			
+			if (result == false) iterators.pop();
+		} while (result == false && iterators.isEmpty() == false);
+		
+		return result;
+	}
+
+	@Override
+	public Element previous() {
+		Holder<Element> element = Holder.of(null);
+		do {
+			element = iterators.peek().previous().extract((ele) -> {
+				return Holder.of(ele);
+			}, (lst) -> {
+				// Ignore empty sublists.
+				if (lst.size() != 0) iterators.push(lst.listIterator());
+				
+				return null;
+			});
+		} while (element == null && hasPrevious());
+
+		if (element == null) throw new NoSuchElementException();
+		
+		return element.getValue();
+	}
+
+	@Override
+	public int nextIndex() {
+		return iterators.peek().nextIndex();
+	}
+
+	@Override
+	public int previousIndex() {
+		return iterators.peek().previousIndex();
+	}
+
+	@Override
+	public void remove() {
+		iterators.peek().remove();
+	}
+
+	@Override
+	public void set(Element e) {
+		iterators.peek().set(Either.left(e));
+	}
+
+	@Override
+	public void add(Element e) {
+		iterators.peek().add(Either.left(e));
+	}
+}
\ No newline at end of file
-- 
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