Could clojure.walk/walk be less lazy?

Question

I noticed that clojure.walk/walk is perhaps lazier internally than it necessarily needs to be. It uses several lazy (map) calls whose output then gets fully consumed.

Would it be considered to change these calls to either (mapv) or the transducer arity of (map) for performance considerations?

Here is a quick diff of a rough suggestion of changes:

diff --git a/src/clj/clojure/walk.clj b/src/clj/clojure/walk.clj
index 0f027e7a..96b089f6 100644
--- a/src/clj/clojure/walk.clj
+++ b/src/clj/clojure/walk.clj
@@ -41,13 +41,13 @@ the sorting function."}
   {:added "1.1"}
   [inner outer form]
   (cond
-   (list? form) (outer (with-meta (apply list (map inner form)) (meta form)))
+   (list? form) (outer (with-meta (apply list (mapv inner form)) (meta form)))
    (instance? clojure.lang.IMapEntry form)
    (outer (clojure.lang.MapEntry/create (inner (key form)) (inner (val form))))
-   (seq? form) (outer (with-meta (doall (map inner form)) (meta form)))
+   (seq? form) (outer (with-meta (seq (mapv inner form)) (meta form)))
    (instance? clojure.lang.IRecord form)
      (outer (reduce (fn [r x] (conj r (inner x))) form form))
-   (coll? form) (outer (into (empty form) (map inner form)))
+   (coll? form) (outer (into (empty form) (map inner) form))
    :else (outer form)))

 (defn postwalk
@@ -97,7 +97,7 @@ the sorting function."}
   [m]
   (let [f (fn [[k v]] (if (string? k) [(keyword k) v] [k v]))]
     ;; only apply to maps
-    (postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))
+    (postwalk (fn [x] (if (map? x) (into {} (map f) x) x)) m)))

 (defn stringify-keys
   "Recursively transforms all map keys from keywords to strings."
@@ -105,7 +105,7 @@ the sorting function."}
   [m]
   (let [f (fn [[k v]] (if (keyword? k) [(name k) v] [k v]))]
     ;; only apply to maps
-    (postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))
+    (postwalk (fn [x] (if (map? x) (into {} (map f) x) x)) m)))

Edit: this is somewhat related to some of the changes proposed in 0003-CLJ-1239-protocol-dispatch-for-clojure.walk.patch on CLJ-1239

Answer 1

Please move comments to the original walk performance ask question at

https://ask.clojure.org/index.php/2376/faster-more-flexible-dispatch-for-clojure-walk

Comments

For sure I can, however I understood that that other one is more about the _dispatch_ where this one is about the transformation.

---

it's all going to be part of the same work, no reason to split it up

---

Fair enough, answered there. Thanks for the directions!