> On Jun 3, 2019, at 11:52 AM, Eric Griffis <ded...@gmail.com> wrote:
> Several times now, I've run into one or another form of the following problem:
>
> Say I want to build primitives to
>
> declare an "interface" as a list of names, and
> implement and use those names at run time in a limited scope
The `implement` macro needs to place its identifiers (say, `say`) inside the
lexical context of the calling site, so that they bind other code coming in
from the calling site (for instance, `(say 'hello)`). Below, the submodules are
not essential for the example, but are meant to show that the module (or file)
boundaries don't affect the result.
#lang racket
(module interface racket
(provide interface)
(define-syntax (interface stx)
(syntax-case stx ()
[(_ id member-id ...) #'(define-syntax id #'(member-id ...))])))
(module implement racket
(require (for-syntax racket/syntax))
(provide implement)
(define-syntax (implement stx)
(syntax-case stx ()
[(_ class-id def ... expr)
(with-syntax ([(id ...) (for/list ([stx (syntax-e (syntax-local-value
#'class-id))])
(format-id #'expr "~a" (syntax->datum stx)))])
#'(letrec ([id def] ...) expr))])))
(require 'interface 'implement)
(interface Speaker say speak)
(implement Speaker displayln (say 'hello) speak)
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