improve message

src/coq_elpi_builtins_synterp.ml

@@ -443,12 +443,18 @@ module SynterpAction = struct
     | Some action -> ignore @@ replay1 action state; replay state
 
   let wrong_synterp_action x a =
-    synterp_interp_error Pp.(str "The elpi program did perform" ++ spc () ++ pp_action a ++ spc () ++
-      str" at parsing time, while at execution time it tried to perform" ++ spc () ++ str x ++ str(". "^common_err))
+    synterp_interp_error Pp.(str "At parsing time, the program did perform action:" ++ fnl () ++
+      pp_action a ++ fnl () ++
+      str"while at execution time it tried to perform action:" ++ fnl () ++
+      str x ++ fnl () ++
+      strbrk common_err)
   let check_inconsistent_synterp_action eq ppx ppy x y a =
     if not (eq x y) then
-      synterp_interp_error Pp.(str "The elpi program did perform" ++ spc () ++ pp_action a ++ spc () ++
-        str" at parsing time and execution, but on different inputs" ++ spc () ++ ppx x ++ str " != " ++ ppy y ++ str(". "^common_err))
+      synterp_interp_error Pp.(str "The program did perform action:" ++ fnl () ++
+      pp_action a ++ fnl () ++
+      str"at both parsing and execution time, but on different inputs:" ++ fnl () ++
+      ppx x ++ str " != " ++ ppy y ++ fnl () ++
+      strbrk common_err)
 
   let check_inconsistent_synterp_action_string =
     check_inconsistent_synterp_action (=) Pp.str Pp.str