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

diff --git a/lib/pipeline.nit b/lib/pipeline.nit
index 0ca08b2..54be22b 100644
--- a/lib/pipeline.nit
+++ b/lib/pipeline.nit
@@ -35,7 +35,7 @@ redef interface Iterator[E]
 	# Filter: sort with a given `comparator`.
 	# Important: require O(n) memory.
 	#
-	#    assert ["a", "c", "b"].iterator.sort_with(alpha_comparator).to_a  == ["a", "b", "c"]
+	#     assert ["a", "c", "b"].iterator.sort_with(alpha_comparator).to_a  == ["a", "b", "c"]
 	fun sort_with(comparator: Comparator): Iterator[E]
 	do
 		var a = self.to_a
@@ -73,6 +73,8 @@ redef interface Iterator[E]
 	# When the first iterator is terminated, the second is started.
 	#
 	#     assert ([1..20[.iterator + [20..40[.iterator).to_a	     ==  ([1..40[).to_a
+	#
+	# SEE: `Iterator2`
 	fun +(other: Iterator[E]): Iterator[E]
 	do
 		return new PipeJoin[E](self, other)
@@ -80,7 +82,7 @@ redef interface Iterator[E]
 
 	# Alternate each item with `e`.
 	#
-	#    assert [1,2,3].iterator.alternate(0).to_a		     ==  [1,0,2,0,3]
+	#     assert [1,2,3].iterator.alternate(0).to_a		     ==  [1,0,2,0,3]
 	fun alternate(e: E): Iterator[E]
 	do
 		return new PipeAlternate[E](self, e)
@@ -88,7 +90,7 @@ redef interface Iterator[E]
 
 	# Filter: reject a given `item`.
 	#
-	#    assert [1,1,2,1,3].iterator.skip(1).to_a		     ==  [2,3]
+	#     assert [1,1,2,1,3].iterator.skip(1).to_a		     ==  [2,3]
 	fun skip(item: E): Iterator[E]
 	do
 		return new PipeSkip[E](self, item)
@@ -159,6 +161,95 @@ redef interface Iterator[E]
 	end
 end
 
+# Concatenates a sequence of iterators.
+#
+# Wraps an iterator of sub-iterators and iterates over the elements of the
+# sub-iterators.
+#
+# ~~~nit
+# var i: Iterator[Int]
+# var empty = new Array[Int]
+#
+# i = new Iterator2[Int]([
+# 	[1, 2, 3].iterator,
+# 	empty.iterator,
+# 	[4, 5].iterator
+# ].iterator)
+# assert i.to_a == [1, 2, 3, 4, 5]
+#
+# i = new Iterator2[Int]([
+# 	empty.iterator,
+# 	[42].iterator,
+# 	empty.iterator
+# ].iterator)
+# assert i.to_a == [42]
+# ~~~
+#
+# SEE: `Iterator::+`
+class Iterator2[E]
+	super Iterator[E]
+
+	# The inner iterator over sub-iterators.
+	var inner: Iterator[Iterator[E]]
+
+	redef fun finish
+	do
+		var i = current_iterator
+		if i != null then i.finish
+	end
+
+	redef fun is_ok
+	do
+		var i = current_iterator
+		if i == null then return false
+		return i.is_ok
+	end
+
+	redef fun item
+	do
+		var i = current_iterator
+		assert i != null
+		return i.item
+	end
+
+	redef fun next
+	do
+		var i = current_iterator
+		assert i != null
+		i.next
+	end
+
+	redef fun start
+	do
+		var i = current_iterator
+		if i != null then i.start
+	end
+
+	private var previous_iterator: nullable Iterator[E] = null
+
+	private fun current_iterator: nullable Iterator[E]
+	do
+		if previous_iterator == null then
+			# Get the first sub-iterator.
+			if inner.is_ok then
+				previous_iterator = inner.item
+				previous_iterator.start
+				inner.next
+			else
+				return null
+			end
+		end
+		# Get the first sub-iterator that has a current item.
+		while inner.is_ok and not previous_iterator.is_ok do
+			previous_iterator.finish
+			previous_iterator = inner.item
+			previous_iterator.start
+			inner.next
+		end
+		return previous_iterator
+	end
+end
+
 # Wraps an iterator to skip nulls.
 #
 # ~~~nit