ocaml: sequence protocol — seq_to_list coercion in HO dispatch + sequence-* primitives

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

hosts/ocaml/lib/sx_primitives.ml

@@ -2112,4 +2112,89 @@ let () =
     | [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)"))
+    | _ -> raise (Eval_error "hash-table-merge!: expected (dst src)"));
+  (* Phase 11: sequence protocol *)
+  let seq_to_list v =
+    match v with
+    | Nil -> List []
+    | List _ -> v
+    | Vector arr -> List (Array.to_list arr)
+    | String s ->
+      let chars = ref [] in
+      String.iter (fun c -> chars := String (String.make 1 c) :: !chars) s;
+      List (List.rev !chars)
+    | _ -> v
+  in
+  register "seq-to-list" (fun args ->
+    match args with
+    | [v] -> seq_to_list v
+    | _ -> raise (Eval_error "seq-to-list: expected 1 arg"));
+  register "sequence-to-list" (fun args ->
+    match args with
+    | [v] -> seq_to_list v
+    | _ -> raise (Eval_error "sequence-to-list: expected 1 arg"));
+  register "sequence-to-vector" (fun args ->
+    match args with
+    | [v] -> (match seq_to_list v with List xs -> Vector (Array.of_list xs) | x -> x)
+    | _ -> raise (Eval_error "sequence-to-vector: expected 1 arg"));
+  register "sequence-length" (fun args ->
+    match args with
+    | [String s] -> Integer (String.length s)
+    | [Vector arr] -> Integer (Array.length arr)
+    | [v] -> (match seq_to_list v with
+        | List xs -> Integer (List.length xs)
+        | _ -> raise (Eval_error "sequence-length: expected sequence"))
+    | _ -> raise (Eval_error "sequence-length: expected 1 arg"));
+  register "sequence-ref" (fun args ->
+    match args with
+    | [String s; Integer i] ->
+      if i < 0 || i >= String.length s
+      then raise (Eval_error (Printf.sprintf "sequence-ref: index %d out of bounds" i))
+      else String (String.make 1 (String.get s i))
+    | [String s; Number n] ->
+      let i = int_of_float n in
+      if i < 0 || i >= String.length s
+      then raise (Eval_error (Printf.sprintf "sequence-ref: index %d out of bounds" i))
+      else String (String.make 1 (String.get s i))
+    | [v; idx] ->
+      let lst = seq_to_list v in
+      let i = (match idx with Integer n -> n | Number n -> int_of_float n | _ -> raise (Eval_error "sequence-ref: index must be number")) in
+      (match lst with
+       | List xs ->
+         (try List.nth xs i
+          with _ -> raise (Eval_error (Printf.sprintf "sequence-ref: index %d out of bounds" i)))
+       | _ -> raise (Eval_error "sequence-ref: expected sequence"))
+    | _ -> raise (Eval_error "sequence-ref: expected (seq index)"));
+  register "sequence-append" (fun args ->
+    match args with
+    | [String s1; String s2] -> String (s1 ^ s2)
+    | [v1; v2] ->
+      let l1 = seq_to_list v1 in
+      let l2 = seq_to_list v2 in
+      (match l1, l2 with
+       | List xs1, List xs2 -> List (xs1 @ xs2)
+       | _ -> raise (Eval_error "sequence-append: expected sequences"))
+    | _ -> raise (Eval_error "sequence-append: expected 2 args"));
+  register "in-range" (fun args ->
+    match args with
+    | [Integer n] ->
+      let rec build i acc = if i < 0 then acc else build (i-1) (Integer i :: acc) in
+      List (build (n-1) [])
+    | [Number n] ->
+      let hi = int_of_float n in
+      let rec build i acc = if i < 0 then acc else build (i-1) (Integer i :: acc) in
+      List (build (hi-1) [])
+    | [Integer lo; Integer hi] ->
+      let rec build i acc = if i < lo then acc else build (i-1) (Integer i :: acc) in
+      List (build (hi-1) [])
+    | [Number lo; Number hi] ->
+      let lo_i = int_of_float lo and hi_i = int_of_float hi in
+      let rec build i acc = if i < lo_i then acc else build (i-1) (Integer i :: acc) in
+      List (build (hi_i-1) [])
+    | [Integer lo; Integer hi; Integer step] ->
+      if step = 0 then raise (Eval_error "in-range: step cannot be zero");
+      let rec build i acc =
+        if (step > 0 && i >= hi) || (step < 0 && i <= hi) then acc
+        else build (i + step) (Integer i :: acc) in
+      List (List.rev (build lo []))
+    | _ -> raise (Eval_error "in-range: expected (end) or (start end) or (start end step)"))