migrate async.manifold to Engine protocol

src/nodely/api/v0.clj

@@ -3,6 +3,7 @@
   (:require
    [nodely.data]
    [nodely.engine.applicative :as applicative]
+   [nodely.engine.async.manifold-engine :as engine.async.manifold-engine]
    [nodely.engine.async.virtual-futures-engine :as engine.async.virtual-futures-engine]
    [nodely.engine.core :as engine-core]
    [nodely.engine.core-async.iterative-scheduling-engine :as engine.core-async.iterative-scheduling-engine]
@@ -57,15 +58,6 @@
                                     nodely.engine.core-async.lazy-scheduling]
            :cause                 e}))))
 
-(def manifold-failure
-  (delay
-   (try (require 'nodely.engine.manifold)
-        (catch Exception e
-          {:msg                   "Could not locate manifold on classpath."
-           ::error                :missing-ns
-           ::requested-namespaces '[nodely.engine.manifold]
-           :cause                 e}))))
-
 (def promesa-failure
   (delay
    (try (require 'nodely.engine.applicative.promesa)
@@ -81,9 +73,8 @@
                                      ::eval-key-channel     true}
    :core-async.iterative-scheduling {::protocol-engine?     true
                                      ::instance-constructor engine.core-async.iterative-scheduling-engine/->CoreAsyncIterativeSchedulingEngine}
-   :async.manifold                  {::ns-name              'nodely.engine.manifold
-                                     ::opts-fn              (constantly nil)
-                                     ::enable-deref         manifold-failure}
+   :async.manifold                  {::protocol-engine?     true
+                                     ::instance-constructor engine.async.manifold-engine/->AsyncManifoldEngine}
    :applicative.promesa             {::ns-name              'nodely.engine.applicative
                                      ::opts-fn              #(assoc % ::applicative/context
                                                                     (var-get (resolve 'nodely.engine.applicative.promesa/context)))

src/nodely/engine/async/manifold_engine.clj

@@ -0,0 +1,44 @@
+(ns nodely.engine.async.manifold-engine
+  (:require
+   [nodely.engine.protocols :as engine.protocols]))
+
+(def ^:private impl-ns 'nodely.engine.manifold)
+
+(def enable-deref
+  "A delay yielding nil when the manifold implementation can be loaded, or a
+  failure map describing the missing dependency otherwise."
+  (delay
+   (try
+     (require impl-ns)
+     nil
+     (catch Exception e
+       {:msg                   "Could not locate manifold on classpath."
+        ::error                :missing-ns
+        ::requested-namespaces [impl-ns]
+        :cause                 e}))))
+
+(defn- impl
+  "Lazily loads the implementation namespace and resolves `fn-name` within it."
+  [fn-name]
+  (requiring-resolve (symbol (name impl-ns) (name fn-name))))
+
+(deftype AsyncManifoldEngine []
+  engine.protocols/Engine
+  (-eval [_engine env k _opts]
+    ((impl 'eval) env k))
+
+  (-eval-key [_engine env k _opts]
+    ((impl 'eval-key) env k))
+
+  (-eval-key-channel [_engine _env _k _opts]
+    (throw (UnsupportedOperationException.
+            "Engine :async.manifold does not support eval-key-channel.")))
+
+  (-eval-key-channel-supported? [_engine]
+    false)
+
+  (-enable-deref [_engine]
+    enable-deref)
+
+  (-prepare-opts [_engine _opts]
+    nil))

test/nodely/api_test.clj

@@ -128,7 +128,7 @@
           5
           (api/eval-key env :z {::api/engine :async.manifold})))))
     (testing-require-delay
-     nodely.engine.manifold nodely.api.v0/manifold-failure
+     nodely.engine.manifold nodely.engine.async.manifold-engine/enable-deref
      "Kaboom! We don't have manifold for pretend" :test-manifold-failure
      (t/testing "without manifold on the classpath"
        (t/testing "attempting to use manifold"