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Re: Dynamic variables

Will>Neither the deep-binding nor the shallow-binding implementation
Will>in terms of DYNAMIC-WIND seems capable of supporting a tail-call

	Unless, as usual, one is willing to test at such tail-calls
	whether they redefine a dynamic variable, and if they do,
	one does -not- save the corresponding binding since it would
	be restored uselessly.
	Price: more tests at runtime.
	Evaluation: (1) calling and dynamically binding infinitely many
	variables is not properly tail-recursive since only tail-recursive
	calls that re-bind a variable can be performed properly;
	(2) calling with N (N is finite) different dynamic variables
	is properly tail-recursive "modulo" N.

	So a "tail-call semantics" for CALL-WITH-DYNAMIC-BINDING is possible.
	Most French Lisp systems actually used this technique.