Correct reduction without an init value.

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project will be documented in this file. This change
 log follows the conventions of [keepachangelog.com](http://keepachangelog.com/).
 
 ## [Unreleased]
+### Fixed
+- Correctly implement reduce semantics for reductions without an init value.
 
 ## [0.1.1] - 2016-08-18
 ### Fixed

src/pjstadig/reducible_stream.clj

@@ -36,7 +36,21 @@
     (reify
       clojure.lang.IReduce
       (reduce [this f]
-        (.reduce this f (f)))
+        (io!
+         (with-open [stream (io/input-stream stream)]
+           (let [stream (cond-> stream
+                          open (open))]
+             (try
+               (let [decoded (->> (repeatedly #(decoder stream ::eof))
+                                  (take-while (complement #{::eof})))]
+                 (if (seq decoded)
+                   (reduce f (first decoded) (rest decoded))
+                   (f)))
+               (finally
+                 (if close
+                   (close stream)
+                   (if (instance? Closeable stream)
+                     (.close ^Closeable stream)))))))))
       clojure.lang.IReduceInit
       (reduce [this f init]
         (io!

test/pjstadig/reducible_stream_test.clj

@@ -20,18 +20,27 @@
                   (lines-decoder stream eof))
         close (fn [stream]
                 (swap! calls conj :close))
-        result (->> (lines-stream "UTF-8" "blah" "blah" "blah")
+        result (->> (lines-stream "UTF-8" "first" "second" "third")
                     (decode! decoder {:open open :close close})
                     (into [] (take 1)))]
     (is (= 1 (count result))
         "should return only one item")
     (is (= [:open :decoder :close] @calls)
         "should consume only one item"))
-  (is (= "blahblahblah"
-         (reduce str
-                 (->> (lines-stream "UTF-8" "blah" "blah" "blah")
+  (is (= "firstsecondthird"
+         (reduce (fn
+                   ([] "no-arg")
+                   ([a b] (str a b)))
+                 (->> (lines-stream "UTF-8" "first" "second" "third")
                       (decode! lines-decoder {:open lines-open}))))
-      "should work when init is not provided"))
+      "should take first item when init is not provided")
+  (is (= "no-arg"
+         (reduce (fn
+                   ([] "no-arg")
+                   ([a b] (str a b)))
+                 (->> (lines-stream "UTF-8")
+                      (decode! lines-decoder {:open lines-open}))))
+      "should call no-arg reducer when collection is empty"))
 
 (deftest t-decode!-as-seq
   (let [calls (atom [])
@@ -43,7 +52,7 @@
                   (lines-decoder stream eof))
         close (fn [stream]
                 (swap! calls conj :close))
-        result (->> (lines-stream "UTF-8" "blah" "blah" "blah")
+        result (->> (lines-stream "UTF-8" "first" "second" "third")
                     (decode! decoder {:open open :close close})
                     (take 1))]
     (is (= 1 (count result))