4 files changed, 53 insertions, 0 deletions
diff --git a/lib/drl/ast.ml b/lib/drl/ast.ml
new file mode 100644
index 0000000..d7eb089
--- /dev/null
+++ b/lib/drl/ast.ml
@@ -0,0 +1,3 @@
+open Sexplib.Std
+
+type query = Base of string | Project of string list * query [@@deriving sexp]
diff --git a/lib/drl/executor.ml b/lib/drl/executor.ml
new file mode 100644
index 0000000..e472ec5
--- /dev/null
+++ b/lib/drl/executor.ml
@@ -0,0 +1,33 @@
+open Utilities.Result
+
+let page_limit = 16
+
+(* [mg:rel] names a relation on the session's branch; a bare name, one the session created. *)
+let path_of (ctx : Sublanguage_context.t) name =
+  match String.index_opt name ':' with
+  | None -> ctx.session#namespace ^ "\\" ^ name
+  | Some i ->
+      String.concat "\\"
+        [ "";
+          "branch";
+          ctx.session#branch;
+          "multigroup";
+          String.sub name 0 i;
+          "relation";
+          String.sub name (i + 1) (String.length name - i - 1) ]
+
+let rec compile ctx = function
+  | Ast.Base name -> RNT.Base (path_of ctx name)
+  | Ast.Project (attributes, query) -> RNT.Project (compile ctx query, attributes)
+
+let execute (ctx : Sublanguage_context.t) query =
+  let* relation = RNT.execute ctx.kernel (compile ctx query) in
+  Fun.protect
+    ~finally:(fun () -> RNT.release relation)
+    (fun () ->
+      let* cursor = RNT.enumerate relation in
+      Fun.protect
+        ~finally:(fun () -> RNT.release cursor)
+        (fun () ->
+          let* {RNT.tuples; exhausted} = RNT.fetch cursor page_limit in
+          Ok (Sublanguage_types.Cursor {rows= tuples; has_more= not exhausted}) ) )
diff --git a/lib/drl/parser.ml b/lib/drl/parser.ml
new file mode 100644
index 0000000..f7d4512
--- /dev/null
+++ b/lib/drl/parser.ml
@@ -0,0 +1,10 @@
+module Error = struct
+  open Condition
+
+  let parse_error msg = condition "parse-error" msg empty
+end
+
+let of_sexp sexp =
+  match Ast.query_of_sexp sexp with
+  | q -> Ok q
+  | exception exn -> Error (Error.parse_error (Printexc.to_string exn))
diff --git a/lib/drl/sublanguage.ml b/lib/drl/sublanguage.ml
new file mode 100644
index 0000000..64b25cc
--- /dev/null
+++ b/lib/drl/sublanguage.ml
@@ -0,0 +1,7 @@
+type configuration = unit
+type ast = Ast.query
+
+let name = "drl"
+let parse _ = Ok ()
+let parse_sexp = Parser.of_sexp
+let execute = Executor.execute