X-Git-Url: http://nitlanguage.org

diff --git a/lib/standard/ropes.nit b/lib/standard/ropes.nit
index b5697bd..b493de9 100644
--- a/lib/standard/ropes.nit
+++ b/lib/standard/ropes.nit
@@ -17,6 +17,29 @@ module ropes
 
 intrude import string
 
+# Used when searching for a particular node
+# Returns the path to the node from the root of the rope
+# Also, the node and the offset for seeked position in the rope
+private class Path
+	# Leaf found
+	var leaf: Leaf
+	# Offset in leaf
+	var offset: Int
+	# Stack of the nodes traversed, and the path used
+	var stack: List[PathElement]
+end
+
+# An element for a Path, has the concat node and whether or not
+# left or right child was visited.
+private class PathElement
+	# Visited node
+	var node: Concat
+	# Was the left child visited ?
+	var left = false
+	# Was the right child visited ?
+	var right = false
+end
+
 # A node for a Rope
 private abstract class RopeNode
 	# Length of the node
@@ -64,3 +87,95 @@ private class Leaf
 
 end
 
+# Basic structure, binary tree with a root node.
+#
+# Also shared services by subsequent implementations.
+abstract class Rope
+	super Text
+
+	# Root node, entry point of a Rope.
+	private var root: RopeNode
+
+	# Empty Rope
+	init do from("")
+
+	# Creates a new Rope with `s` as root
+	init from(s: String) do
+		if s isa RopeString then root = s.root else root = new Leaf(s.as(FlatString))
+	end
+
+	private init from_root(r: RopeNode)
+	do
+		root = r
+	end
+
+	redef fun length do return root.length
+
+	# Path to the Leaf for `position`
+	private fun node_at(position: Int): Path
+	do
+		assert position >= 0 and position < length
+		return get_node_from(root.as(not null), 0, position, new List[PathElement])
+	end
+
+	# Builds the path to Leaf at position `seek_pos`
+	private fun get_node_from(node: RopeNode, curr_pos: Int, seek_pos: Int, stack: List[PathElement]): Path
+	do
+		assert curr_pos >= 0
+		if node isa Leaf then return new Path(node, seek_pos - curr_pos, stack)
+		node = node.as(Concat)
+
+		if node.left != null then
+			var next_pos = curr_pos + node.left.length
+			stack.add(new PathElement(node))
+			if next_pos > seek_pos then
+				stack.last.left = true
+				return get_node_from(node.left.as(not null), curr_pos, seek_pos, stack)
+			end
+			stack.last.right = true
+			return get_node_from(node.right.as(not null), next_pos, seek_pos, stack)
+		else
+			var vis = new PathElement(node)
+			vis.right = true
+			stack.add(vis)
+			return get_node_from(node.right.as(not null), curr_pos, seek_pos, stack)
+		end
+	end
+
+end
+
+# Rope that cannot be modified
+class RopeString
+	super Rope
+	super String
+
+	redef fun to_s do return self
+
+	# Adds `s` at the end of self
+	fun append(s: String): String
+	do
+		if self.is_empty then return s
+		return new RopeString.from_root(append_to_path(root,s))
+	end
+
+	# Builds a new path from root to the rightmost node with s appended
+	private fun append_to_path(node: RopeNode, s: String): RopeNode
+	do
+		var cct = new Concat
+		if node isa Leaf then
+			cct.left = node
+			if s isa FlatString then cct.right = new Leaf(s) else cct.right = s.as(RopeString).root
+		else if node isa Concat then
+			var right = node.right
+			if node.left != null then cct.left = node.left.as(not null)
+			if right == null then
+				if s isa FlatString then cct.right = new Leaf(s) else cct.right = s.as(RopeString).root
+			else
+				cct.right = append_to_path(right, s)
+			end
+		end
+		return cct
+	end
+
+end
+