Compatibility with OCaml < 5

Use a fake implementation of mutexes and domains in this case to avoid a
dependency on the threads library

Author: vouillon

lib/dune

@@ -3,3 +3,8 @@
  (synopsis "Pure OCaml regular expression library")
  (libraries seq)
  (public_name re))
+
+(copy_files#
+ (enabled_if
+  (< %{ocaml_version} 5))
+ (files fake/*))

lib/fake/domain.ml

@@ -0,0 +1,5 @@
+module DLS = struct
+  let new_key f = ref (f())
+  let set x y = x := y
+  let get x = !x
+end

lib/fake/mutex.ml

@@ -0,0 +1,26 @@
+(*
+   RE - A regular expression library
+
+   Copyright (C) 2025 Jerome Vouillon
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation, with
+   linking exception; either version 2.1 of the License, or (at
+   your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with this library; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+*)
+
+type t = unit
+
+let create _ = ()
+let lock _ = ()
+let unlock _ = ()