add check function

src/letsqlite.ml

@@ -125,6 +125,10 @@ let finalize = function
                     Rc.check (S.finalize s); v
                     )
 
+let check s = match s with
+| Failed e -> raise (S.SqliteError (Rc.to_string e))
+| Norm (v,_) -> (v,s)
+
 let exec db s = prepare db s () >>$ step
 let reexec db s = reprepare db s @>$ step
 let bsrc l = bind_values l @>$ step @>$ reset @>$ clear_bindings

src/letsqlite.mli

@@ -162,6 +162,10 @@ val finalize : 'a stmt_m -> 'a
 (** [finalize] raises an exception if the execution failed, and [V]
     otherwise. *)
 
+val check : 'a stmt_m -> ('a * 'a stmt_m)
+(** [check] checks if the statement is an error value and throws an
+    exception if it is. If it is not, then it returns [(V,S)]. *)
+
 val bind_values : Sqlite3.Data.t list -> ('a,'a) monad_fun
 (** [bind_values l] binds each index of [l] to a positional parameter
     in [S]. *)