try to avoid races again (cf. 8c37cb84065f and fd3a36e48b09);
(* Title: Pure/ML-Systems/use_context.ML
Author: Makarius
Common context for "use" operations (compiler invocation).
*)
type use_context =
{tune_source: string -> string,
name_space: ML_Name_Space.T,
str_of_pos: int -> string -> string,
print: string -> unit,
error: string -> unit};