Syntax tree nodes for language module types, of type
Ast.module_type. The basic nodes are:
<:module_type< $mt1$ . $mt2$ >>: access in module.
<:module_type< $mt1$ $mt2$ >>: application.
<:module_type< functor ( $s$ : $mt1$ ) -> $mt2$ >>: functor.
<:module_type< $lid:i$ >>: identifier starting with a
lowercase letter.
<:module_type< sig $list:sil$ end >>: signature.
<:module_type< $uid:i$ >>: identifier starting with an
uppercase letter.
<:module_type< $mt$ with $list:wcl$ >>: module type
with constraint.