improve bin pretty printing of errors

src/bin/cli.ml

@@ -1,11 +1,34 @@
 open Cmdliner
 open Trace
 
+let error_pp out (e : error) =
+    let open JSON_string_utils in
+  let message =
+    let opt = e |> member "message" |> string in
+    let msg = Option.unopt ~default:"" opt in
+    ": " ^ msg in
+  let error_code =
+    let error_code = e |> member "error_code" in
+    match error_code with
+    | `Null -> ""
+    | _ -> " (" ^ (J.to_string error_code) ^ ")" in
+  let title =
+    let opt = e |> member "title" |> string in
+    Option.unopt ~default:"" opt in
+  let data =
+    let data = e |> member "data" in
+    match data with
+    | `Null -> ""
+    | _ -> " " ^ (J.to_string data) ^ "\n" in
+  Format.fprintf out "%s%s%s.\n%s" title error_code message data
+
+
 let toplevel x =
   match x with
   | Trace.Ok ((), annotations) -> ignore annotations; ()
-  | Error ss ->
+  | Error ss -> (
       Format.printf "%a%!" error_pp (ss ())
+    )
 
 let main =
   let term = Term.(const print_endline $ const "Ligo needs a command. Do ligo --help") in