diff --git a/prototype/Doubt/Cofree.swift b/prototype/Doubt/Cofree.swift
index 7e3378463..864ac8bd5 100644
--- a/prototype/Doubt/Cofree.swift
+++ b/prototype/Doubt/Cofree.swift
@@ -3,3 +3,15 @@
 public enum Cofree<B> {
 	case Unroll(B)
 }
+
+
+// MARK: - Comonad
+
+extension Cofree {
+	var extract: B {
+		switch self {
+		case let .Unroll(b):
+			return b
+		}
+	}
+}