make dynaload more ClojureScript friendly

Author: swannodette

src/main/cljs/cljs/spec/impl/gen.cljc

@@ -8,13 +8,26 @@
 
 (ns cljs.spec.impl.gen
   (:refer-clojure :exclude [delay])
-  (:require [cljs.core :as c]))
+  (:require [cljs.core :as c]
+            [clojure.string :as string]))
 
 (defmacro dynaload [[quote s]]
-  `(if (c/exists? ~s)
-     ~(vary-meta s assoc :cljs.analyzer/no-resolve true)
-     (fn [& ~'args]
-       (throw (js/Error. (str "Var " '~s " is not on the classpath"))))))
+  (let [xs     (string/split (namespace s) #"\.")
+        cnt    (count xs)
+        checks (map
+                 (fn [n xs]
+                   `(c/exists? ~(symbol (string/join "." (take n xs)))))
+                 (range 2 cnt)
+                 (repeat xs))]
+    `(cljs.spec.impl.gen/LazyVar.
+       (fn []
+         (if (and ~@checks (c/exists? ~s))
+           ~(vary-meta s assoc :cljs.analyzer/no-resolve true)
+           (throw
+             (js/Error.
+               (str "Var " '~s " does not exist, "
+                    (namespace '~s) " never required")))))
+       nil)))
 
 (defmacro delay
   "given body that returns a generator, returns a
@@ -28,7 +41,7 @@
   [s]
   (let [fqn (symbol "clojure.test.check.generators" (name s))
         doc (str "Lazy loaded version of " fqn)]
-    `(let [g# (c/delay (dynaload '~fqn))]
+    `(let [g# (dynaload '~fqn)]
        (defn ~s
          ~doc
          [& ~'args]
@@ -47,7 +60,7 @@
   [s]
   (let [fqn (symbol "clojure.test.check.generators" (name s))
         doc (str "Fn returning " fqn)]
-    `(let [g# (c/delay (dynaload '~fqn))]
+    `(let [g# (dynaload '~fqn)]
        (defn ~s
          ~doc
          [& ~'args]

src/main/cljs/cljs/spec/impl/gen.cljs

@@ -13,24 +13,34 @@
                    [cljs.spec.impl.gen :as gen :refer [dynaload lazy-combinators lazy-prims]])
   (:require [cljs.core :as c]))
 
+(deftype LazyVar [f ^:mutable cached]
+  IDeref
+  (-deref [this]
+    (if-not (nil? cached)
+      cached
+      (let [x (f)]
+        (when-not (nil? x)
+          (set! cached x))
+        x))))
+
 (def ^:private quick-check-ref
-  (c/delay (dynaload 'clojure.test.check/quick-check)))
+  (dynaload 'clojure.test.check/quick-check))
 
 (defn quick-check
   [& args]
   (apply @quick-check-ref args))
 
 (def ^:private for-all*-ref
-  (c/delay (dynaload 'clojure.test.check.properties/for-all*)))
+  (dynaload 'clojure.test.check.properties/for-all*))
 
 (defn for-all*
   "Dynamically loaded clojure.test.check.properties/for-all*."
   [& args]
   (apply @for-all*-ref args))
 
-(let [g? (c/delay (dynaload 'clojure.test.check.generators/generator?))
-      g (c/delay (dynaload 'clojure.test.check.generators/generate))
-      mkg (c/delay (dynaload 'clojure.test.check.generators/->Generator))]
+(let [g? (dynaload 'clojure.test.check.generators/generator?)
+      g (dynaload 'clojure.test.check.generators/generate)
+      mkg (dynaload 'clojure.test.check.generators/->Generator)]
   (defn- generator?
     [x]
     (@g? x))