first cut of the collection methods in the standard library in http://confluence.jetbrains.net/display/JET/Standard+Library along with a little testlib to test them. Still a few TODO things and tidy up (and am sure a few more methods could be very handy too) but its getting Kool :)

testlib/test/CollectionApiCheck.kt

@@ -0,0 +1,34 @@
+namespace test.apicheck
+
+import java.util.*
+
+trait Traversable<T> {
+
+  /** Returns true if any elements in the collection match the given predicate */
+  fun any(predicate: fun(T): Boolean) : Boolean
+
+  /** Returns true if all elements in the collection match the given predicate */
+  fun all(predicate: fun(T): Boolean) : Boolean
+
+  /** Returns the first item in the collection which matches the given predicate or null if none matched */
+  fun find(predicate: fun(T): Boolean) : T?
+
+  /** Returns a new collection containing all elements in this collection which match the given predicate */
+  // TODO using: Collection<T> for the return type - I wonder if this exact type could be
+  // deduced somewhat from the This.Type; e.g. returning Set on a Set, Array on Array etc
+  fun filter(predicate: fun(T): Boolean) : Collection<T>
+
+  /** Performs the given operation on each element inside the collection */
+  fun foreach(operation: fun(element: T) : Unit)
+
+  /** Returns a new collection containing the results of applying the given function to each element in this collection */
+  fun <T, R> java.lang.Iterable<T>.map(transform : fun(T) : R) : Collection<R>
+}
+
+/**
+TODO try use delegation here to make sure we implement all the methods in the Traversable API
+
+class ListImpl<T>(coll: ArrayList<out T>) : Traversable<T> by coll {
+}
+
+*/