diff --git a/Array.js b/Array.js
index 5d868dc..364258c 100644
--- a/Array.js
+++ b/Array.js
@@ -482,6 +482,35 @@ object.Mixin('ArrayProtoMixin', 'soft', {
 			this.constructor.zip(this, func, ...arrays)
 			: this.constructor.zip(func, this, ...arrays) },
 
+	// Insert new values between elements of an array
+	//
+	//	.between(value)
+	//		-> array
+	//
+	//	.between(func)
+	//		-> array
+	//
+	//	func([a, b], from_index, to_index, array)
+	//		-> elem
+	//
+	between: function(func){
+		var res = []
+		// NOTE: we skip the last element...
+		for(var i=0; i < this.length; i+=1){
+			var pair = new Array(2)
+			i in this ?
+				res.push(pair[0] = this[i])
+				: (res.length += 1)
+			if(i+1 >= this.length){
+				break }
+			i+1 in this
+				&& (pair[1] = this[i+1])
+			res.push(
+				typeof(func) == 'function' ?
+					func.call(this, pair, i, res.length, this)
+					: func) }
+		return res },
+
 	// get iterator over array...
 	//
 	//	Array.iter()
diff --git a/Promise.js b/Promise.js
index 9d2e7ab..6346de7 100644
--- a/Promise.js
+++ b/Promise.js
@@ -294,6 +294,11 @@ object.Constructor('IterablePromise', Promise, {
 			.then(function(){ 
 				return res }) },
 
+	// XXX BETWEEN...
+	between: function(func){
+		// XXX
+	},
+
 	// XXX .chain(..) -- see generator.chain(..)
 
 	flat: function(depth=1){
diff --git a/generator.js b/generator.js
index d9593ca..169c28e 100644
--- a/generator.js
+++ b/generator.js
@@ -223,6 +223,8 @@ object.Mixin('GeneratorMixin', 'soft', {
 	reduce: makeGenerator('reduce'),
 	reduceRight: makeGenerator('reduceRight'),
 
+	between: makeGenerator('between'),
+
 	// XXX add .toString(..) ???
 	forEach: function(func){
 		var that = this
@@ -403,6 +405,19 @@ object.Mixin('GeneratorProtoMixin', 'soft', {
 	greduce: function*(func, res){
 		yield this.reduce(...arguments) },
 
+	between: stoppable(function*(func){
+		var i = 0
+		var j = 0
+		var prev
+		for(var e of this){
+			if(i > 0){
+				yield typeof(func) == 'function' ?
+					func.call(this, [prev, e], i-1, i + j++, this)
+					: func }
+			prev = e
+			yield e
+			i++ } }),
+
 	// NOTE: this is a special case in that it will unwind the generator...
 	// NOTE: this is different from <array>.forEach(..) in that this will
 	// 		return the resulting array.
@@ -502,6 +517,9 @@ object.Mixin('AsyncGeneratorMixin', 'soft', {
 	map: makeGenerator('async', 'map'),
 	filter: makeGenerator('async', 'filter'),
 	reduce: makeGenerator('async', 'reduce'),
+
+	// XXX TEST...
+	between: makeGenerator('async', 'between'),
 })
 
 var AsyncGeneratorProtoMixin =
@@ -559,6 +577,11 @@ object.Mixin('AsyncGeneratorProtoMixin', 'soft', {
 			return [] })
 		return state },
 
+	// XXX BETWEEN...
+	between: async function(func){
+		// XXX
+	},
+
 	// XXX TEST...
 	chain: async function*(...next){
 		yield* next
diff --git a/package.json b/package.json
index 2df51fc..2fc09a2 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ig-types",
-  "version": "6.16.4",
+  "version": "6.17.0",
   "description": "Generic JavaScript types and type extensions...",
   "main": "main.js",
   "scripts": {