Improve the error handling situation (#71)

* Sketches of a condition system

* `Condition.condition` -> `Condition.t`

* Migrate `NT` over

* Migrate `Branch` over

* Migrate `Sublanguage` et al. over

* Migrate the PRL over

* Migrate the DRL over

* Migrate the DML over

* Have `Qualified_name.try_parse` return a `Condition.t`

* Migrate the DDL over

* Migrate the VCL over

* Migrate the SCL over

* Migrate the ICL over

* Migrate the parsers over

* Just inherit the errors from NT and the sublanguages

* Migrate `Management.Physical` over

* Migrate `Configuration` over

* Migrate `Management.Branch` over

* Migrate `Transport` over

* Migrate `System` over

* Migrate `Server` over

* Include messages on on all conditions

* A prettier stringifier

1 files changed, 8 insertions, 14 deletions

diff --git a/lib/scl/executor.ml b/lib/scl/executor.ml
index 6848091..e40fde6 100644
--- a/lib/scl/executor.ml
+++ b/lib/scl/executor.ml
@@ -13,28 +13,22 @@ type exec_result =
 module Make (NT : Nt.S) = struct
   module DrlExec = Drl.Executor.Make (NT)
 
-  type error =
-    | ParseError of string
-    | QueryError of DrlExec.error
-    | CursorError of string
-
-  let sexp_of_error e =
-    let open Sexplib.Sexp in
-    match e with
-    | ParseError s -> List [ Atom "parse-error"; Atom s ]
-    | QueryError e -> DrlExec.sexp_of_error e
-    | CursorError s -> List [ Atom "cursor-error"; Atom s ]
+  module Error = struct
+    open Condition
+    (* TODO: more structure *)
+    let cursor_error msg = condition "cursor-error" msg empty
+  end
 
   let ( let* ) = Result.bind
 
   let execute (ctx : Sublanguage_context.t) (stmt : Ast.statement) :
-      (exec_result, error) result =
+      (exec_result, Condition.t) result =
     ignore default_batch;
     match stmt with
     | Ast.Begin _ ->
-        Error (CursorError "cursors not yet implemented")
+        Error (Error.cursor_error "cursors not yet implemented")
     | Ast.Fetch _ ->
-        Error (CursorError "cursors not yet implemented")
+        Error (Error.cursor_error "cursors not yet implemented")
     | Ast.Close _ ->
         let* () = Ok () in
         Ok (Closed ctx.branch#multigroups)