> On Apr 3, 2018, at 2:31 PM, Kevin Forchione <lyss...@gmail.com> wrote:
>
> Hi Guys,
> Does anyone have an analogous example for let-syntax to something as simple
> as this?
>
> (let ([a 3]) a)
>
> Something like….
>
> (let-syntax ([a 3]) ….)
>
> At which point I’m stumped as to what expression in the body would return 3.
> There are no examples in the Reference.
Others have pointed out different things you could put on the right-hand-side
of the let-binding, iow, where the 3 is.
However, your original question was about what body expression would make
`(let-syntax ([a 3]) ....)` return 3. The function that lets you do that is
`syntax-local-value`. It's used in macros to get the compile-time values of
things defined with define-syntax or let-syntax.
(let-syntax ([a 3])
(define-syntax m
(lambda (stx)
#`(quote #,(syntax-local-value #'a))))
(m))
While this compile-time value can be any normal value like 3, most of the time
you want it to be a function. If it's a function, the macro expander will call
that function when it sees that identifier in the code, to expand the macro.
However, if you want two macros to communicate a compile-time value between
them, you can have one of them generate a `let-syntax` or `define-syntax` to
define that value, and have the other use `syntax-local-value` to get it.
Alex Knauth
> Thanks!
> Kevin
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