erlang: lists keylist BIFs (keyfind/keymember/keydelete/keyreplace/keystore/keytake/keysort) (809/809)

Adds the tuple-keyed list family to lib/erlang/lists-ext.sx: act on
first match, key compare via == (er-equal?), non-tuples/short tuples
pass through. keysort/2 reuses the stable merge sort + full term
order. keytake/3 returns {value, Tuple, Rest} | false. All seven
registered through the er-register-builtin-bifs! wrapper so they
survive mid-run registry resets. lists_ext suite 17 -> 38.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/erlang/lists-ext.sx

@@ -141,6 +141,114 @@
         (er-ext-dedup
           (er-ext-msort (er-cons->sxlist lst) er-ext-term-le))))))
 
+;; ── keylists (lists of tuples keyed on element N, 1-indexed) ──────
+;; keyfind/keymember/keydelete/keyreplace/keystore/keytake/keysort.
+;; Key comparison is == (er-equal?), matching the standard lib. Only
+;; the FIRST matching tuple is acted on. Non-tuples / tuples shorter
+;; than N never match and are passed through unchanged.
+(define
+  er-ext-tup-elem
+  (fn (tup n)
+    (if (er-tuple? tup)
+      (let ((es (get tup :elements)))
+        (if (and (>= n 1) (<= n (len es))) (nth es (- n 1)) nil))
+      nil)))
+
+(define
+  er-ext-key-match?
+  (fn (key n tup)
+    (and
+      (er-tuple? tup)
+      (>= n 1)
+      (<= n (len (get tup :elements)))
+      (er-equal? key (nth (get tup :elements) (- n 1))))))
+
+(define
+  er-ext-keyfind
+  (fn (key n lst)
+    (cond
+      (er-nil? lst) (er-mk-atom "false")
+      (er-cons? lst)
+        (if (er-ext-key-match? key n (get lst :head))
+          (get lst :head)
+          (er-ext-keyfind key n (get lst :tail)))
+      :else (er-mk-atom "false"))))
+
+(define
+  er-ext-keydelete
+  (fn (key n lst)
+    (cond
+      (er-nil? lst) (er-mk-nil)
+      (er-cons? lst)
+        (if (er-ext-key-match? key n (get lst :head))
+          (get lst :tail)
+          (er-mk-cons (get lst :head) (er-ext-keydelete key n (get lst :tail))))
+      :else lst)))
+
+(define
+  er-ext-keyreplace
+  (fn (key n lst new)
+    (cond
+      (er-nil? lst) (er-mk-nil)
+      (er-cons? lst)
+        (if (er-ext-key-match? key n (get lst :head))
+          (er-mk-cons new (get lst :tail))
+          (er-mk-cons (get lst :head) (er-ext-keyreplace key n (get lst :tail) new)))
+      :else lst)))
+
+(define
+  er-ext-keystore
+  (fn (key n lst new)
+    (cond
+      (er-nil? lst) (er-mk-cons new (er-mk-nil))
+      (er-cons? lst)
+        (if (er-ext-key-match? key n (get lst :head))
+          (er-mk-cons new (get lst :tail))
+          (er-mk-cons (get lst :head) (er-ext-keystore key n (get lst :tail) new)))
+      :else lst)))
+
+(define
+  er-bif-lists-keyfind
+  (fn (vs) (er-ext-keyfind (nth vs 0) (nth vs 1) (nth vs 2))))
+
+(define
+  er-bif-lists-keymember
+  (fn (vs)
+    (er-bool (not (er-atom? (er-ext-keyfind (nth vs 0) (nth vs 1) (nth vs 2)))))))
+
+(define
+  er-bif-lists-keydelete
+  (fn (vs) (er-ext-keydelete (nth vs 0) (nth vs 1) (nth vs 2))))
+
+(define
+  er-bif-lists-keyreplace
+  (fn (vs) (er-ext-keyreplace (nth vs 0) (nth vs 1) (nth vs 2) (nth vs 3))))
+
+(define
+  er-bif-lists-keystore
+  (fn (vs) (er-ext-keystore (nth vs 0) (nth vs 1) (nth vs 2) (nth vs 3))))
+
+(define
+  er-bif-lists-keytake
+  (fn (vs)
+    (let ((key (nth vs 0)) (n (nth vs 1)) (lst (nth vs 2)))
+      (let ((hit (er-ext-keyfind key n lst)))
+        (if (er-atom? hit)
+          (er-mk-atom "false")
+          (er-mk-tuple
+            (list (er-mk-atom "value") hit (er-ext-keydelete key n lst))))))))
+
+(define
+  er-bif-lists-keysort
+  (fn (vs)
+    (let ((n (nth vs 0)) (lst (nth vs 1)))
+      (er-sxlist->cons
+        (er-ext-msort
+          (er-cons->sxlist lst)
+          (fn (a b)
+            (er-bool
+              (not (er-ext-lt? (er-ext-tup-elem b n) (er-ext-tup-elem a n))))))))))
+
 ;; ── register ──────────────────────────────────────────────────────
 ;; Hook into er-register-builtin-bifs! rather than registering once:
 ;; the registry can be reset + rebuilt mid-run (tests/runtime.sx does
@@ -150,7 +258,14 @@
   (fn ()
     (er-register-pure-bif! "lists" "sort" 1 er-bif-lists-sort)
     (er-register-pure-bif! "lists" "sort" 2 er-bif-lists-sort)
-    (er-register-pure-bif! "lists" "usort" 1 er-bif-lists-usort)))
+    (er-register-pure-bif! "lists" "usort" 1 er-bif-lists-usort)
+    (er-register-pure-bif! "lists" "keyfind" 3 er-bif-lists-keyfind)
+    (er-register-pure-bif! "lists" "keymember" 3 er-bif-lists-keymember)
+    (er-register-pure-bif! "lists" "keydelete" 3 er-bif-lists-keydelete)
+    (er-register-pure-bif! "lists" "keyreplace" 4 er-bif-lists-keyreplace)
+    (er-register-pure-bif! "lists" "keystore" 4 er-bif-lists-keystore)
+    (er-register-pure-bif! "lists" "keytake" 3 er-bif-lists-keytake)
+    (er-register-pure-bif! "lists" "keysort" 2 er-bif-lists-keysort)))
 
 (define er-ext-prev-register-builtins er-register-builtin-bifs!)
 (define er-register-builtin-bifs!