CLJS-1531: realized? for lazy-seq

- Add support for IPending to LazySeq.
- Change param from d to x in places (no longer just delay)
- Unit test via lazy-seq built with cons cells

Author: mfikes

src/main/cljs/cljs/core.cljs

@@ -650,9 +650,9 @@
 
 (defprotocol IPending
   "Protocol for types which can have a deferred realization. Currently only
-  implemented by Delay."
-  (^boolean -realized? [d]
-    "Returns true if a value for d has been produced, false otherwise."))
+  implemented by Delay and LazySeq."
+  (^boolean -realized? [x]
+    "Returns true if a value for x has been produced, false otherwise."))
 
 (defprotocol IWatchable
   "Protocol for types that can be watched. Currently only implemented by Atom."
@@ -3014,6 +3014,10 @@ reduces them without incurring seq initialization"
         (set! fn nil)
         s)))
 
+  IPending
+  (-realized? [x]
+    (not fn))
+
   IWithMeta
   (-with-meta [coll meta] (LazySeq. meta fn s __hash))
 
@@ -9195,7 +9199,7 @@ reduces them without incurring seq initialization"
     value)
 
   IPending
-  (-realized? [d]
+  (-realized? [x]
     (not f)))
 
 (defn ^boolean delay?
@@ -9211,8 +9215,8 @@ reduces them without incurring seq initialization"
 
 (defn ^boolean realized?
   "Returns true if a value has been produced for a delay or lazy sequence."
-  [d]
-  (-realized? d))
+  [x]
+  (-realized? x))
 
 (defn- preserving-reduced
   [rf]

src/test/cljs/cljs/core_test.cljs

@@ -1639,6 +1639,19 @@
     (is (= '(2 3) (next (range 1 4))))
     ))
 
+(deftest test-lazy-seq-realized?
+  (testing "Testing LazySeq IPending"
+    (let [xs (lazy-seq
+               (cons 1
+                 (lazy-seq
+                   (cons 2
+                     (lazy-seq (cons 3 nil))))))]
+      (is (not (realized? xs)))
+      (is (not (realized? (rest xs))))
+      (is (realized? xs))
+      (is (not (realized? (nthrest xs 2))))
+      (is (realized? (rest xs))))))
+
 (deftest test-chunked
   (let [r (range 64)
         v (into [] r)]