[sledge] Use more standard interface for Trace.parse

Summary:
`('a, exn) result` is a more widely used type than with something
custom in place of `exn`, e.g. by the `Result` operations.

Reviewed By: mbouaziz

Differential Revision: D14322627

fbshipit-source-id: e2ed167ed

sledge/src/config.ml

@@ -8,6 +8,10 @@
 (** Configuration options *)
 
 let trace_conv =
+  let parse s =
+    Trace.parse s
+    |> Result.map_error ~f:(fun _ -> `Msg ("Invalid trace spec: " ^ s))
+  in
   let print fs {trace_all; trace_mods_funs} =
     let pf fmt = Format.fprintf fs fmt in
     if trace_all then pf "*"
@@ -22,7 +26,7 @@ let trace_conv =
               if fun_enabled then pf "+%s.%s" mod_name fun_name
               else pf "-%s.%s" mod_name fun_name ) )
   in
-  (Trace.parse, print)
+  (parse, print)
 
 type t =
   { compile_only: bool

sledge/src/trace/trace.ml

@@ -75,7 +75,7 @@ let parse s =
                   ~data:{trace_mod= Some enabled; trace_funs= default} )
       in
       Ok {none with trace_mods_funs}
-  with Assert_failure _ -> Error (`Msg ("Invalid trace spec: " ^ s))
+  with Assert_failure _ as exn -> Error exn
 
 let init ?(margin = 300) ~config:c () =
   Format.set_margin margin ;

sledge/src/trace/trace.mli

@@ -23,7 +23,7 @@ type config =
 
 val none : config
 val all : config
-val parse : string -> (config, [> `Msg of string]) result
+val parse : string -> (config, exn) result
 
 val init : ?margin:int -> config:config -> unit -> unit
 (** Initialize the configuration of debug tracing. *)