just checking in

src/main/scala/com/htmlism/ShiftExtractor.scala

@@ -0,0 +1,39 @@
+package com.htmlism
+
+trait BitExtractor[A] {
+  self =>
+
+  def length: Int
+
+  def unapply(n: Int): Option[A]
+
+  def >>[B](that: BitExtractor[B]): BitExtractor[(A, B)] =
+    new BitExtractor[(A, B)] {
+      def length: Int = self.length + that.length
+
+      def unapply(n: Int): Option[(A, B)] =
+        for {
+          b <- that.unapply(n)
+          shifted = n >> that.length
+          a <- self.unapply(shifted)
+        } yield (a, b)
+    }
+}
+
+object AtomExtractor {
+  def pow(ex: Int, acc: Int = 1): Int =
+    if (ex == 0)
+      acc
+    else
+      pow(ex - 1, acc * 2)
+}
+
+abstract class PrimitiveBitExtractor(val length: Int) extends BitExtractor[Int] {
+  private lazy val mask = AtomExtractor.pow(length) - 1
+
+  def unapply(n: Int): Option[Int] = Some(n & mask)
+}
+
+object OneBit extends PrimitiveBitExtractor(1)
+object TwoBits extends PrimitiveBitExtractor(2)
+object ThreeBits extends PrimitiveBitExtractor(3)