From d28b40a26fbdc8649accac91043b05333ec26cf1 Mon Sep 17 00:00:00 2001
From: James Hamlin <jfhamlin@gmail.com>
Date: Mon, 13 Oct 2025 13:57:20 -0700
Subject: [PATCH] Fix MapKeySeq reduce operations (#125)

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.
---
 pkg/lang/persistentarraymap.go      | 37 ++++++++++++++++++++++++++++-
 test/glojure/test_glojure/basic.glj | 20 ++++++++++++++++
 2 files changed, 56 insertions(+), 1 deletion(-)

diff --git a/pkg/lang/persistentarraymap.go b/pkg/lang/persistentarraymap.go
index bf1cad4..d47d6f0 100644
--- a/pkg/lang/persistentarraymap.go
+++ b/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 {
diff --git a/test/glojure/test_glojure/basic.glj b/test/glojure/test_glojure/basic.glj
index 2c5ca22..8f2328b 100644
--- a/test/glojure/test_glojure/basic.glj
+++ b/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)