Re: A macro containing a mini-macro?

[rain1@airmail.cc]

On 2018-09-13 23:04, HiPhish wrote:
> Hello Schemers,
> 
> I have written a small macro for writing test specifications:
> 
>     (define-syntax test-cases
>       (syntax-rules ()
>         ((_ title
>            (given (byte byte* ...))
>            ...)
>          (begin
>            (test-begin title)
>            (call-with-values (λ () (open-bytevector-output-port))
>              (λ (out get-bv)
>                (pack given out)
>                (let ((received (get-bv))
>                      (expected (u8-list->bytevector '(byte byte* 
> ...))))
>                  (test-assert (bytevector=? received expected)))))
>            ...
>            (test-end title)))))
> 
> The idea is that I can specify a series of test cases where each case 
> consists
> of an object and a sequence of bytes which this object is to be 
> serialized to:
> 
>     (test-cases "Single precision floating point numbers"
>       (+3.1415927410125732 (#xCA #b01000000 #b01001001 #b00001111 
> #b11011011))
>       (-3.1415927410125732 (#xCA #b11000000 #b01001001 #b00001111
> #b11011011)))
> 
> This works fine, but sometimes there is a sequence of the same bytes 
> and it
> would be more readable if I could write something like this:
> 
>     ((make-vector 16 0) (#xDC (16 #x00)))
> 
> instead of writing out 16 times `#x00`. This would require being able 
> to make
> a distinction in the pattern whether `byte` is of the pattern
> 
>     byte
> 
> or
> 
>     (count byte)
> 
> and if it's the latter construct a list of `count` `byte`s (via 
> `(make-list
> count byte)` for example) and splice it in. This distinction needs to 
> be made
> for each byte specification because I want to mix actual bytes and 
> these "RLE-
> encoded" byte specifications.
> 
> So I guess what I'm looking for is to have a `syntax-rules` inside a 
> `syntax-
> rules` in a way. Can this be done?

You can implement the DSL that transforms bytevector descriptions like 
(#xDC (16 #x00)) into a bytevector as a procedure, suppose we call it 
byte-dsl. Then you only need to change u8-list->bytevector with 
byte-dsl. This lets you do what you wanted without the difficult task of 
macros inside macros.