Session with stream control sublanguage (#55)

SCL adds cursor-based streaming to Sakura so clients can consume DRL query results incrementally in bounded batches rather than all at once. Three statements: Begin, Fetch, and Close. `open`, `advance`, and `release` cursors backed by a session registry that suspends the generator between calls. SCL is just an optional consumption layer above the existing algebra.

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/scl/sublanguage.ml b/lib/scl/sublanguage.ml
new file mode 100644
index 0000000..7098ced
--- /dev/null
+++ b/lib/scl/sublanguage.ml
@@ -0,0 +1,26 @@
+module Make (Storage : Management.Physical.S) = struct
+  module Exec = Executor.Make(Storage)
+
+  type storage = Storage.t
+  type ast     = Ast.statement
+  type error   = Exec.error
+
+  let name = "scl"
+
+  let parse_sexp sexp =
+    match Parser.of_sexp sexp with
+    | Ok r -> Ok r
+    | Error (Parser.ParseError s) -> Error (Exec.ParseError s)
+
+  let execute storage db ast =
+    Exec.execute storage db ast
+    |> Result.map (function
+      | Executor.Batch { cursor_id; rows; has_more } ->
+        Sublanguage.Cursor { cursor_id; rows; has_more }
+      | Executor.Closed db ->
+        Sublanguage.Transition (db, "cursor closed"))
+
+  let sexp_of_error = Exec.sexp_of_error
+end
+
+module Memory = Make(Management.Physical.Memory)