At Wed, 29 Jul 2015 07:00:54 -0700 (PDT), Klaus Ostermann wrote:
> Units are not allowed to export macros, presumably because the unit wiring
> takes place after the macro expansion.
>
> I have a unit and would like to define a few macros based on the interface of
> that unit.
>
> Right now I copy&paste my macros into every file where I wire the unit, such
> as in
>
> ...
> (define-values/invoke-unit/infer some-unit@)
>
> (define-syntax-rule (foo t) (...something-from-the-unit-interface))
>
> Surely there is a better way to do this.
>
> But how?
You can include macros in a unit signature. For example,
(define-signature s^
(;; A plain export:
call-with-catch
;; Macro that uses the export:
(define-syntaxes (with-catch)
(syntax-rules ()
[(_ body0 body ...)
(call-with-catch
(lambda () body0 body ...))]))))
defines the signature of a unit that provides `call-with-catch`, but
also arranges that any importing context can use `with-catch`.
Given
(define-unit u@
(import)
(export s^)
(define (call-with-catch thunk)
(with-handlers ([exn:fail? (lambda (exn) exn)])
(thunk))))
then this works:
(define-values/invoke-unit/infer u@)
(with-catch (/ 0))
The `define-signature` form currently only recognizes `define-syntaxes`
as the form for adding macros to a signature, which is why I used that
form plus `syntax-rules` instead of `define-syntax-rules`.
--
You received this message because you are subscribed to the Google Groups
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
