[CM] spear <-> grace

[Bill Schottstaedt]

I was thinking maybe s7 could have a *decimal-point* variable or something,
but there are ambiguities:

> (define-macro (hi a) `(+ ,1 ,a))
hi
> (hi 2)
3

Is ,1 one-tenth or a needlessly (but legally) unquoted one?

This is sort of like using "@" to start a variable name:

(define-macro (hi @foo . foo) `(list , at foo))

or 

> (define-macro (hi @) `(+ 1 ,@))
unexpected close paren: ...