spec: mutable hash tables (make-hash-table/ref/set!/delete!/etc)

Phase 10 — 11 primitives: make-hash-table, hash-table?, hash-table-set!,
hash-table-ref, hash-table-delete!, hash-table-size, hash-table-keys,
hash-table-values, hash-table->alist, hash-table-for-each, hash-table-merge!.
OCaml HashTable variant; JS Map-based. 28 tests, both hosts green.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/ocaml/lib/sx_primitives.ml

@@ -2052,4 +2052,64 @@ let () =
         n := !n lsr 1
       done;
       Integer !bits
-    | _ -> raise (Eval_error "integer-length: expected (integer)"))
+    | _ -> raise (Eval_error "integer-length: expected (integer)"));
+
+  (* Phase 10: mutable hash tables *)
+  register "make-hash-table" (fun _ -> HashTable (Hashtbl.create 16));
+  register "hash-table?" (fun args ->
+    match args with
+    | [HashTable _] -> Bool true
+    | [_] -> Bool false
+    | _ -> Bool false);
+  register "hash-table-set!" (fun args ->
+    match args with
+    | [HashTable ht; k; v] ->
+      (try Hashtbl.replace ht k v
+       with _ ->
+         (* fallback: scan for physically equal key *)
+         let found = ref false in
+         Hashtbl.iter (fun ek _ -> if ek == k then (Hashtbl.replace ht ek v; found := true)) ht;
+         if not !found then Hashtbl.replace ht k v);
+      Nil
+    | _ -> raise (Eval_error "hash-table-set!: expected (ht key val)"));
+  register "hash-table-ref" (fun args ->
+    match args with
+    | [HashTable ht; k] ->
+      (try Hashtbl.find ht k
+       with Not_found -> raise (Eval_error ("hash-table-ref: key not found")))
+    | [HashTable ht; k; default] ->
+      (try Hashtbl.find ht k with Not_found -> default)
+    | _ -> raise (Eval_error "hash-table-ref: expected (ht key) or (ht key default)"));
+  register "hash-table-delete!" (fun args ->
+    match args with
+    | [HashTable ht; k] -> Hashtbl.remove ht k; Nil
+    | _ -> raise (Eval_error "hash-table-delete!: expected (ht key)"));
+  register "hash-table-size" (fun args ->
+    match args with
+    | [HashTable ht] -> Integer (Hashtbl.length ht)
+    | _ -> raise (Eval_error "hash-table-size: expected (ht)"));
+  register "hash-table-keys" (fun args ->
+    match args with
+    | [HashTable ht] -> List (Hashtbl.fold (fun k _ acc -> k :: acc) ht [])
+    | _ -> raise (Eval_error "hash-table-keys: expected (ht)"));
+  register "hash-table-values" (fun args ->
+    match args with
+    | [HashTable ht] -> List (Hashtbl.fold (fun _ v acc -> v :: acc) ht [])
+    | _ -> raise (Eval_error "hash-table-values: expected (ht)"));
+  register "hash-table->alist" (fun args ->
+    match args with
+    | [HashTable ht] ->
+      List (Hashtbl.fold (fun k v acc -> List [k; v] :: acc) ht [])
+    | _ -> raise (Eval_error "hash-table->alist: expected (ht)"));
+  register "hash-table-for-each" (fun args ->
+    match args with
+    | [HashTable ht; fn] ->
+      Hashtbl.iter (fun k v -> ignore (!Sx_types._cek_call_ref fn (List [k; v]))) ht;
+      Nil
+    | _ -> raise (Eval_error "hash-table-for-each: expected (ht fn)"));
+  register "hash-table-merge!" (fun args ->
+    match args with
+    | [HashTable dst; HashTable src] ->
+      Hashtbl.iter (fun k v -> Hashtbl.replace dst k v) src;
+      Nil
+    | _ -> raise (Eval_error "hash-table-merge!: expected (dst src)"))

hosts/ocaml/lib/sx_types.ml

@@ -74,6 +74,7 @@ and value =
   | Parameter of parameter  (** R7RS parameter — dynamic binding via kont-stack provide frames. *)
   | Vector of value array  (** R7RS vector — mutable fixed-size array. *)
   | StringBuffer of Buffer.t  (** Mutable string buffer — O(1) amortized append. *)
+  | HashTable of (value, value) Hashtbl.t  (** Mutable hash table with arbitrary keys. *)
 
 (** CEK machine state — record instead of Dict for performance.
     5 fields × 55K steps/sec = 275K Hashtbl allocations/sec eliminated. *)
@@ -493,6 +494,7 @@ let type_of = function
   | Parameter _    -> "parameter"
   | Vector _       -> "vector"
   | StringBuffer _ -> "string-buffer"
+  | HashTable _    -> "hash-table"
 
 let is_nil = function Nil -> true | _ -> false
 let is_lambda = function Lambda _ -> true | _ -> false
@@ -839,3 +841,4 @@ let rec inspect = function
   | VmFrame f -> Printf.sprintf "<vm-frame:ip=%d base=%d>" f.vf_ip f.vf_base
   | VmMachine m -> Printf.sprintf "<vm-machine:sp=%d frames=%d>" m.vm_sp (List.length m.vm_frames)
   | StringBuffer buf -> Printf.sprintf "<string-buffer:%d>" (Buffer.length buf)
+  | HashTable ht -> Printf.sprintf "<hash-table:%d>" (Hashtbl.length ht)