T> use
	this function to transform values of any type <I>tyseq <TT>t</TT></I>
	into a tree the inspector can display. Raises <TT>Type</TT> if
	the type of <TT><I>f</I></TT> is not of the required form.
	This includes the case that <TT><I>t</I></TT> is not an abstract type,
	or that <TT><I>f</I></TT> is not fully polymorphic in the type
	arguments <I>tyseq</I> to <TT><I>t</I></TT>.
	Note that these rules also preclude <TT><I>f</I></TT> from being
	<EM>too polymorphic</EM>, i.e. being of type <TT>'a -> string