unikernel/duniverse/ocaml-caqti/caqti/lib-template/row_mult.ml

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+(* Copyright (C) 2017--2024  Petter A. Urkedal <paurkedal@gmail.com>
+ *
+ * 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, either version 3 of the License, or (at your
+ * option) any later version, with the LGPL-3.0 Linking Exception.
+ *
+ * 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
+ * and the LGPL-3.0 Linking Exception along with this library.  If not, see
+ * <http://www.gnu.org/licenses/> and <https://spdx.org>, respectively.
+ *)
+
+(** Multiplicities of zero, one, and many. *)
+
+type +'m t = (* not GADT due to variance *)
+ | Zero
+ | One
+ | Zero_or_one
+ | Zero_or_more
+constraint 'm = [< `Zero | `One | `Many]
+
+type zero = [`Zero]
+type one = [`One]
+type zero_or_one = [`Zero | `One]
+type zero_or_more = [`Zero | `One | `Many]
+
+let zero : [> `Zero] t = Zero
+let one : [> `One] t = One
+let zero_or_one : [> `Zero | `One] t = Zero_or_one
+let zero_or_more : ([> `Zero | `One | `Many] as 'a) t = Zero_or_more
+
+let only_zero : [< `Zero] t -> unit =
+  function Zero -> () | _ -> assert false
+let only_one : [< `One] t -> unit =
+  function One -> () | _ -> assert false
+let only_zero_or_one : [< `Zero | `One] t -> unit =
+  function Zero | One -> () | _ -> assert false
+
+let expose = function
+ | Zero -> `Zero
+ | One -> `One
+ | Zero_or_one -> `Zero_or_one
+ | Zero_or_more -> `Zero_or_more
+
+let can_be_zero = function
+ | One -> false
+ | Zero | Zero_or_one | Zero_or_more -> true
+
+let can_be_many = function
+ | Zero | One | Zero_or_one -> false
+ | Zero_or_more -> true