drop, fixes #53

core.js

@@ -821,3 +821,18 @@ export function cycle(coll) {
     while (true) yield* coll;
   });
 }
+
+// private
+function iterator(x) {
+  return x[Symbol.iterator]();
+}
+
+export function drop(n, xs) {
+  return new LazyIterable(function* () {
+    let iter = iterator(xs);
+    for (let x = 0; x < n; x++) {
+      iter.next();
+    }
+    yield* iter;
+  });
+}

resources/clava/core.edn

@@ -26,6 +26,7 @@
   disj_BANG_
   dissoc
   dissoc_BANG_
+  drop
   empty
   es6_iterator
   even_QMARK_

test/clava/compiler_test.cljs

@@ -1019,5 +1019,11 @@
   (is (= 1 (jsv! '(nth [1 2 3] 0))))
   (is (eq :default (jsv! '(nth [1 2 3] 5 :default)))))
 
+(deftest drop-test
+  (let [dropped (jsv! '(drop 3 (range 6)))]
+    (is (eq [3 4 5] (vec dropped)))
+    ;; iterating over dropped second time, still works:
+    (is (eq [3 4 5] (vec dropped)))))
+
 (defn init []
   (cljs.test/run-tests 'clava.compiler-test 'clava.jsx-test))