fix too restrictive type in CCResult

src/core/CCResult.ml

@@ -24,6 +24,10 @@ let fail_printf format =
     (fun buf -> fail (Buffer.contents buf))
     buf format
 
+(*$T
+  (Error "ohno 42") = (fail_printf "ohno %d" 42)
+*)
+
 let fail_fprintf format =
   let buf = Buffer.create 64 in
   let out = Format.formatter_of_buffer buf in
@@ -31,6 +35,10 @@ let fail_fprintf format =
     (fun out -> Format.pp_print_flush out (); fail (Buffer.contents buf))
     out format
 
+(*$T
+  (Error "ohno 42") = (fail_fprintf "ohno %d" 42)
+*)
+
 let add_ctx msg x = match x with
   | Error e -> Error (e ^ "\ncontext:" ^ msg)
   | Ok x -> Ok x

src/core/CCResult.mli

@@ -34,11 +34,11 @@ val of_exn_trace : exn -> ('a, string) t
     Remember to call [Printexc.record_backtrace true] and compile with the
     debug flag for this to work. *)
 
-val fail_printf : ('a, Buffer.t, unit, ('a, string) t) format4 -> 'a
+val fail_printf : ('a, Buffer.t, unit, ('b, string) t) format4 -> 'a
 (** [fail_printf format] uses [format] to obtain an error message
     and then returns [Error msg] *)
 
-val fail_fprintf : ('a, Format.formatter, unit, ('a, string) t) format4 -> 'a
+val fail_fprintf : ('a, Format.formatter, unit, ('b, string) t) format4 -> 'a
 (** [fail_printf format] uses [format] to obtain an error message
     and then returns [Error msg] *)