> The inspiration for this ,@ is described as
>
> If an `(unquote-splicing <expression> ...)' form appears inside a
> <qq template>, then the <expression>s must evaluate to lists; the
> opening and closing parentheses of the lists are then "stripped
> away" and the elements of the lists are inserted in place of the
> `UNQUOTE-SPLICING' form.
>
> Any `UNQUOTE-SPLICING' or multi-operand `UNQUOTE' form must appear
> only within a list or vector <qq template>.
>
> The following abbreviations may be used:
>
> (quasiquote <qq template>) = `<qq template>
> (unquote <expression>) = ,<expression>
> (unquote-splicing <expression>) = ,@<expression>
>
> Examples:
>
> `(list ,(+ 1 2) 4) => (list 3 4)
>
> (let ((name 'a))
> `(list ,name ',name)) => (list a (quote a))
>
> `(a ,(+ 1 2) ,@(map abs '(4 -5 6)) b) => (a 3 4 5 6 b)
>
> `((foo ,(- 10 3))
> ,@(cdr '(c)) . ,(car '(cons))) => ((foo 7) . cons)
>
> `#(10 5 ,(sqrt 4) ,@(map sqrt '(16 9)) 8)
> => #(10 5 2 4 3 8)
>
> Suggestions for improving the docs?
I find the above much too dense. It introduces three different pseudo
operators in one rush. While tightly related, it should be done step
by step. So this is a criticism of the R6RS docs (being a standard to
be read by Scheme experts), not LilyPond. However, a casual reader
not so fluent in Scheme will tear one's hair if she gets confronted
with your $@ form.
Perhaps it's a bit redundant, but I think that it would help many
readers if some Scheme basics are added to the documentation of $@
*directly*, demonstrating the unquote-splicing mechanism in very basic
examples.
Werner
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