Re: [racket-users] Dynamic-require a compile-time identifier?

[Alex Knauth]

> On Jan 21, 2017, at 6:27 PM, Dupéron Georges  
> wrote:
> 
> I was going to suggest `dynamic-require-for-syntax`, but it seems to do 
> exactly the same thing as `dynamic-require`, i.e. give the value of a phase-0 
> provided identifier. Is this normal?
> 
> The `eval` trick is a good idea, I would say. From the couple of times I have 
> used dynamic-require, I have felt that it was pretty limited concerning 
> shifting phases.
> 
> The thing I found to be the most difficult is to extract the phase 1 value 
> bound to a macro via define-syntax. Following your `eval` idea, I managed to 
> do that using 3D syntax. I suppose it's safe, as the 3D syntax object is 
> created on the fly during `eval` and promptly discarded, therefore it should 
> never need to be marshalled into a compiled file.
> 
> (eval #'(begin
>   (module m racket/base
> (require (for-syntax racket/base) "x.rkt")
> (provide (for-syntax x-val))
> (define-syntax (get-val stx)
>   (syntax-case stx ()
> [(_ name)
>  #`(define-for-syntax name #,(syntax-local-value #'x))]))
> (get-val x-val))
>   (require (for-meta -1 'm))
>   x-val))

If `eval` is inevitable I want to minimize it as much as possible, and I don't 
want to rely on 3d syntax. I think I use eval to define a module that shifts 
the phase by that amount, then dynamic-require from that module instead:

(define (dynamic-require-for-meta mod phase sym)
  (define mod* (resolve-module-path mod))
  (parameterize ([current-namespace (make-base-namespace)])
(eval `(module mod-for-phase reprovide
 (#%module-begin (only-meta-in 0 (for-meta ,phase ,mod*)
(dynamic-require ''mod-for-phase sym)))

(dynamic-require-for-meta "x.rkt" -1 'x)

This isn't meant to require macro transformers; it's only meant to require 
things that were provided for-syntax.

Thanks,
Alex Knauth

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[racket-users] Dynamic-require a compile-time identifier?

[Alex Knauth]

Is there a way to dynamic-require an identifier provided at phase 1?

#file x.rkt
#lang racket
(provide (for-syntax x)) ; x is provided at phase 1
(define-for-syntax x 3)

#file use.rkt
#lang racket
(dynamic-require-from-phase-1 "x.rkt" 'x)
;=> 3

I could do it by defining another module that did the phase shift:

#file x.rkt
#lang racket
(provide (for-syntax x))
(define-for-syntax x 3)

(module* ct racket/base
  (provide (for-meta -1 (all-from-out (submod ".."
  (require (for-meta -1 (submod ".."

#file use.rkt
#lang racket
(dynamic-require '(submod "x.rkt" ct) 'x)

But that requires an extra module to be defined already. I could also do it 
with eval, but that feels wrong and shouldn't be necessary. There should be a 
way to do this without needing eval.

Alex Knauth

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