spec: regular expressions (make-regexp/regexp-match/regexp-replace + split)

Adds 9 regexp primitives to stdlib.regexp. OCaml: SxRegexp(src,flags,Re.re)
using Re.Pcre; $&/$1 capture expansion in replace. JS: native RegExp
with SxRegexp wrapper; regexp-match returns {:match :start :end :groups}.
32 tests in test-regexp.sx, all pass on both hosts.

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

hosts/ocaml/lib/sx_primitives.ml

@@ -2224,6 +2224,127 @@ let () =
       String flags
     | _ -> raise (Eval_error "regex-flags: (regex)"));
 
+  (* make-regexp / regexp? / regexp-match / regexp-match-all / regexp-replace / regexp-replace-all / regexp-split *)
+  let parse_re_flags flags =
+    let opts = ref [] in
+    String.iter (function
+      | 'i' -> opts := `CASELESS :: !opts
+      | 'm' -> opts := `MULTILINE :: !opts
+      | 's' -> opts := `DOTALL :: !opts
+      | _ -> ()) flags;
+    !opts
+  in
+  let make_regexp_value source flags =
+    let opts = parse_re_flags flags in
+    try
+      let compiled = Re.compile (Re.Pcre.re ~flags:opts source) in
+      SxRegexp (source, flags, compiled)
+    with _ -> raise (Eval_error ("make-regexp: invalid pattern: " ^ source))
+  in
+  let match_dict g input =
+    let d = Hashtbl.create 4 in
+    Hashtbl.replace d "match" (String (Re.Group.get g 0));
+    Hashtbl.replace d "start" (Integer (Re.Group.start g 0));
+    Hashtbl.replace d "end" (Integer (Re.Group.stop g 0));
+    Hashtbl.replace d "input" (String input);
+    let count = Re.Group.nb_groups g in
+    let groups = ref [] in
+    for i = count - 1 downto 1 do
+      let s = try Re.Group.get g i with Not_found -> "" in
+      groups := String s :: !groups
+    done;
+    Hashtbl.replace d "groups" (List !groups);
+    Dict d
+  in
+  register "make-regexp" (fun args ->
+    match args with
+    | [String src] -> make_regexp_value src ""
+    | [String src; String flags] -> make_regexp_value src flags
+    | _ -> raise (Eval_error "make-regexp: (pattern [flags])"));
+  register "regexp?" (fun args ->
+    match args with
+    | [SxRegexp _] -> Bool true
+    | [_] -> Bool false
+    | _ -> raise (Eval_error "regexp?: 1 arg"));
+  register "regexp-source" (fun args ->
+    match args with
+    | [SxRegexp (src, _, _)] -> String src
+    | _ -> raise (Eval_error "regexp-source: expected regexp"));
+  register "regexp-flags" (fun args ->
+    match args with
+    | [SxRegexp (_, flags, _)] -> String flags
+    | _ -> raise (Eval_error "regexp-flags: expected regexp"));
+  register "regexp-match" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      (match Re.exec_opt re s with
+       | None -> Nil
+       | Some g -> match_dict g s)
+    | _ -> raise (Eval_error "regexp-match: (regexp string)"));
+  register "regexp-match-all" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      List (List.map (fun g -> match_dict g s) (Re.all re s))
+    | _ -> raise (Eval_error "regexp-match-all: (regexp string)"));
+  register "regexp-replace" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s; String replacement] ->
+      (match Re.exec_opt re s with
+       | None -> String s
+       | Some g ->
+         let buf = Buffer.create (String.length s) in
+         let i = ref 0 in
+         let n = String.length replacement in
+         let expand () =
+           while !i < n do
+             let c = replacement.[!i] in
+             if c = '$' && !i + 1 < n then
+               (match replacement.[!i + 1] with
+                | '&' -> Buffer.add_string buf (Re.Group.get g 0); i := !i + 2
+                | '$' -> Buffer.add_char buf '$'; i := !i + 2
+                | c when c >= '0' && c <= '9' ->
+                  let idx = Char.code c - Char.code '0' in
+                  (try Buffer.add_string buf (Re.Group.get g idx) with Not_found -> ());
+                  i := !i + 2
+                | _ -> Buffer.add_char buf c; incr i)
+             else (Buffer.add_char buf c; incr i)
+           done
+         in
+         Buffer.add_string buf (String.sub s 0 (Re.Group.start g 0));
+         expand ();
+         Buffer.add_string buf (String.sub s (Re.Group.stop g 0)
+           (String.length s - Re.Group.stop g 0));
+         String (Buffer.contents buf))
+    | _ -> raise (Eval_error "regexp-replace: (regexp string replacement)"));
+  register "regexp-replace-all" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s; String replacement] ->
+      let expand g =
+        let buf = Buffer.create (String.length replacement) in
+        let i = ref 0 in
+        let n = String.length replacement in
+        while !i < n do
+          let c = replacement.[!i] in
+          if c = '$' && !i + 1 < n then
+            (match replacement.[!i + 1] with
+             | '&' -> Buffer.add_string buf (Re.Group.get g 0); i := !i + 2
+             | '$' -> Buffer.add_char buf '$'; i := !i + 2
+             | c when c >= '0' && c <= '9' ->
+               let idx = Char.code c - Char.code '0' in
+               (try Buffer.add_string buf (Re.Group.get g idx) with Not_found -> ());
+               i := !i + 2
+             | _ -> Buffer.add_char buf c; incr i)
+          else (Buffer.add_char buf c; incr i)
+        done;
+        Buffer.contents buf
+      in
+      String (Re.replace re ~f:expand s)
+    | _ -> raise (Eval_error "regexp-replace-all: (regexp string replacement)"));
+  register "regexp-split" (fun args ->
+    match args with
+    | [SxRegexp (_, _, re); String s] ->
+      List (List.map (fun x -> String x) (Re.split re s))
+    | _ -> raise (Eval_error "regexp-split: (regexp string)"));
   (* Bitwise operations *)
   register "bitwise-and" (fun args ->
     match args with

hosts/ocaml/lib/sx_types.ml

@@ -80,6 +80,7 @@ and value =
   | Port of sx_port  (** String port — input (string cursor) or output (buffer). *)
   | Rational of int * int  (** Exact rational: numerator, denominator (reduced, denom>0). *)
   | SxSet of (string, value) Hashtbl.t  (** Mutable set keyed by inspect(value). *)
+  | SxRegexp of string * string * Re.re  (** Regexp: source, flags, compiled. *)
 
 (** String input port: source string + mutable cursor position. *)
 and sx_port_kind =
@@ -516,6 +517,7 @@ let type_of = function
   | Port { sp_kind = PortOutput _; _ } -> "output-port"
   | Rational _  -> "rational"
   | SxSet _     -> "set"
+  | SxRegexp _  -> "regexp"
 
 let is_nil = function Nil -> true | _ -> false
 let is_lambda = function Lambda _ -> true | _ -> false
@@ -879,3 +881,4 @@ let rec inspect = function
     Printf.sprintf "<output-port:len=%d%s>" (Buffer.length buf) (if sp_closed then ":closed" else "")
   | Rational (n, d) -> Printf.sprintf "%d/%d" n d
   | SxSet ht -> Printf.sprintf "<set:%d>" (Hashtbl.length ht)
+  | SxRegexp (src, flags, _) -> Printf.sprintf "#/%s/%s" src flags