Fix MapKeySeq reduce operations (#125) (#136)

Implements IReduce and IReduceInit interfaces for MapKeySeq to fix
"No method in multimethod 'coll-reduce' for dispatch value: *lang.MapKeySeq"
error when using mapv on map keys.

Changes:
- Add Reduce and ReduceInit methods to MapKeySeq in pkg/lang/persistentarraymap.go
- Add interface assertions for IReduce and IReduceInit compliance
- Add comprehensive test cases in test/glojure/test_glojure/basic.glj

Fixes issue where operations like (mapv identity (keys some-map)) would fail
due to missing reduce implementation.

Author: jfhamlin

pkg/lang/persistentarraymap.go

@@ -51,7 +51,9 @@ var (
 	_ IReduceInit = (*MapSeq)(nil)
 	_ IDrop       = (*MapSeq)(nil)
 
-	_ ASeq = (*MapKeySeq)(nil)
+	_ ASeq        = (*MapKeySeq)(nil)
+	_ IReduce     = (*MapKeySeq)(nil)
+	_ IReduceInit = (*MapKeySeq)(nil)
 
 	_ ASeq        = (*MapValSeq)(nil)
 	_ IReduce     = (*MapValSeq)(nil)
@@ -563,6 +565,39 @@ func (s *MapKeySeq) HashEq() uint32 {
 	return aseqHashEq(&s.hasheq, s)
 }
 
+func (s *MapKeySeq) Reduce(f IFn) any {
+	count := 0
+	var res any
+	first := true
+	for seq := Seq(s); seq != nil; seq = seq.Next() {
+		count++
+		if first {
+			res = seq.First()
+			first = false
+			continue
+		}
+		res = f.Invoke(res, seq.First())
+		if IsReduced(res) {
+			return res.(IDeref).Deref()
+		}
+	}
+	if count == 0 {
+		return f.Invoke()
+	}
+	return res
+}
+
+func (s *MapKeySeq) ReduceInit(f IFn, init any) any {
+	res := init
+	for seq := Seq(s); seq != nil; seq = seq.Next() {
+		res = f.Invoke(res, seq.First())
+		if IsReduced(res) {
+			return res.(IDeref).Deref()
+		}
+	}
+	return res
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 
 func NewMapValSeq(s ISeq) ISeq {

test/glojure/test_glojure/basic.glj

@@ -108,4 +108,24 @@
   (is (:foo (meta ^:foo #{})))
   (is (:foo (meta ^:foo {}))))
 
+(deftest map-key-seq-reduce
+  (test-that "MapKeySeq implements reduce operations correctly"
+    (let [test-map {:a 1 :b 2 :c 3 :d 4 :e 5}]
+      ;; Test mapv on keys (this was the original failing case)
+      (is (= 5 (count (mapv identity (keys test-map)))))
+      (is (vector? (mapv identity (keys test-map))))
+      
+      ;; Test reduce on keys
+      (is (= 5 (reduce (fn [acc _] (inc acc)) 0 (keys test-map))))
+      
+      ;; Test mapv with transformation on keys
+      (is (= 5 (count (mapv str (keys test-map)))))
+      
+      ;; Test that vals still work correctly
+      (is (= 5 (count (mapv identity (vals test-map)))))
+      (is (= 15 (reduce + (vals test-map))))
+      
+      ;; Test with namespace map keys (the original bug report case)
+      (is (number? (count (mapv str (keys (ns-map *ns*)))))))))
+
 (run-tests)