Merge pull request #16 from kaaninho/plain-lens-functions

Make plain lenses into variadic functions by removing the Lens protocol

Author: kaaninho

src/active/clojure/lens.cljc

@@ -1,51 +1,37 @@
 (ns active.clojure.lens)
 
-(defprotocol Lens
-  "Protocol for types that can be used as a lens, defined by a
-   function to yank some value out of a given data value, and a function
-   to shove an updated value back in."
-  (-yank [lens data])
-  (-shove [lens data v]))
-
 ;; TODO document lens laws
 
 (defn yank
   "Yank a value from the given data value, as defined by the given
    lens."
   [data lens]
-  (-yank lens data))
+  (lens data))
 
 (defn shove
   "Shove a new value v into the given data value, as defined by the
    given lens, and return the updated data structure."
   [data lens v]
-  (-shove lens data v))
-
-;; Keywords are lenses over a map (or object), focusing on the value associated with that keyword.
-(extend-type #?(:clj clojure.lang.Keyword) #?(:cljs cljs.core.Keyword)
-  Lens
-  (-yank [kw data] (kw data))
-  (-shove [kw data v] (assoc data kw v)))
+  (if (keyword? lens)
+    (assoc data lens v)
+    (lens data v)))
 
 (defrecord ExplicitLens
     ^{:private true}
   [yanker shover args]
-  Lens
-  (-yank [lens data] (apply yanker data args))
-  (-shove [lens data v] (apply shover data v args))
   #?@(:clj [clojure.lang.IFn
-            (invoke [this data] (-yank this data))
-            (invoke [this data v] (-shove this data v))
+            (invoke [this data] (apply yanker data args))
+            (invoke [this data v] (apply shover data v args))
             (applyTo [this args]
                      (let [args (object-array args)]
                        (case (count args)
-                         1 (-yank this (aget args 0))
-                         2 (-shove this (aget args 0) (aget args 1))
+                         1 (yanker (aget args 0))
+                         2 (shover (aget args 0) (aget args 1))
                          (throw #?(:clj (java.lang.IllegalArgumentException. (str "invalid number of arguments (" (count args) ") to lens")))
                                 #?(:cljs (str "invalid number of arguments (" (count args) ") to lens"))))))]
       :cljs [IFn
-             (-invoke [this data] (-yank this data))
-             (-invoke [this data v] (-shove this data v))]))
+             (-invoke [this data] (apply yanker data args))
+             (-invoke [this data v] (apply shover data v args))]))
 
 (defn lens
   "Returns a new lens defined by the given yanker function, which
@@ -95,7 +81,6 @@
    value of the last one, in a data structure that the first one is put
    over."
   [l1 & lmore]
-  (assert (not-any? #(not (satisfies? Lens %)) (cons l1 lmore)))
   (loop [res l1
          lmore lmore]
     (if (empty? lmore)

test/active/clojure/lens_test.cljc

@@ -248,10 +248,21 @@
          (lens/shove 'baz lens/id 'bar))))
 
 
-(deftest fct
-  (is (= 1
-         (lens/nel-head [1 2 3 4])))
-  (is (= [5 2 3 4]
-         (lens/nel-head [1 2 3 4] 5)))
-  (is (= [5 2 3 4]
-         (apply lens/nel-head [1 2 3 4] [5]))))
+(deftest explicit-lens-invocation
+  (testing "can use explicit lens like a function, for yank"
+    (is (= 1
+           (lens/nel-head [1 2 3 4])))
+    (is (= 4
+           ((lens/pos 3) [1 2 3 4]))))
+  (testing "can use explicit lens like a function, for shove"
+    (is (= [5 2 3 4]
+           (lens/nel-head [1 2 3 4] 5)))
+    (is (= [1 2 3 5]
+           ((lens/pos 3) [1 2 3 4] 5))))
+  (testing "can apply explicit lens"
+    (is (= [5 2 3 4]
+           (apply lens/nel-head [1 2 3 4] [5])))))
+
+(deftest lens-composition-equality
+  (is (= (lens/>> (lens/pos 3) lens/nel-head)
+         (lens/>> (lens/pos 3) lens/nel-head))))