Evaluate typed queries over persistent maps

src/value.ml

@@ -0,0 +1,45 @@
+type t =
+  | VUnit
+  | VInt of int
+  | VBool of bool
+  | VString of string
+  | VTuple of t list
+  | VRecord of string * (string * t) list
+  | VCollection of t Delta_runtime.Pure_map.t
+
+let rec to_string value =
+  match value with
+  | VUnit -> "unit"
+  | VInt number -> string_of_int number
+  | VBool true -> "true"
+  | VBool false -> "false"
+  | VString text -> Printf.sprintf "%S" text
+  | VTuple items -> "(tuple " ^ Util.join " " (List.map to_string items) ^ ")"
+  | VRecord (name, fields) ->
+      Printf.sprintf "(record:%s %s)" name
+        (Util.join " " (List.map (fun (label, field) -> "(" ^ label ^ " " ^ to_string field ^ ")") fields))
+  | VCollection map ->
+      let entries =
+        List.map (fun (key, item) -> Printf.sprintf "(%d %s)" key (to_string item))
+          (Delta_runtime.Pure_map.bindings map)
+      in
+      "(collection " ^ Util.join " " entries ^ ")"
+
+let collection_of_list entries =
+  List.fold_left
+    (fun map (key, value) ->
+      if Delta_runtime.Pure_map.mem key map then
+        Diagnostic.error Location.none "duplicate key %d in the initial input" key;
+      Delta_runtime.Pure_map.add key value map)
+    Delta_runtime.Pure_map.empty entries
+
+let collection_to_list map = Delta_runtime.Pure_map.bindings map
+
+let equal (left : t) (right : t) = left = right
+
+let field record label =
+  match record with
+  | VRecord (_, fields) -> Util.assoc_opt label fields
+  | _ -> None
+
+let is_collection = function VCollection _ -> true | _ -> false