ImplicitConversions

Refer to scala.util.parsing.combinator.Parsers to construct an AST from the concrete syntax.

The reason for this is that the sequential composition combinator (~) combines its constituents
into a ~. When several ~s are combined, this results in nested ~s (to the left).
The flatten* coercions makes it easy to apply an n-argument function to a nested ~ of
depth n-1

The headOptionTailToFunList converts a function that takes a List[A] to a function that
accepts a ~[A, Option[List[A]]] (this happens when parsing something of the following
shape: p ~ opt("." ~ repsep(p, ".")) -- where p is a parser that yields an A).