Mdx_topSourceToplevel logic for mdx.
The type for configuration values.
val init :
verbose:bool ->
silent:bool ->
verbose_findlib:bool ->
directives:directive list ->
packages:string list ->
predicates:string list ->
unit ->
tinit () is a new configuration value.
eval t p evaluates the toplevel phrase p (possibly spawning on mulitple lines) with the configuration value t.