[racket-users] Language-provided bindings and arrows in DrRacket

[Dupéron Georges]

I'm writing a meta-language (a small extension of scribble/lp2), which 
delegates to a second language. I am using the neat trick suggested to me by 
Alex Knauth [1], but I have trouble getting the arrows to be drawn in DrRacket 
for language "built-ins".

A boiled down version of the language file "MyLang.rkt" follows:

#lang racket
(provide (rename-out [my-module-begin #%module-begin]))
(define-syntax (my-module-begin stx)
  (syntax-case stx ()
[(_ real-lang body)
 (syntax-case (local-expand #'(module m real-lang body) 'top-level (list)) 
()
   [(module nm lng (#%plain-module-begin . body2))
#'(#%plain-module-begin
;; use (only lng) to avoid conflicts with other require
(#%require (only lng))
. body2)])]))

It is used by "m.rkt":

(module m "MyLang.rkt" ;; MyLang acts as a meta-language
  racket/base  ;; which delegates to this language
  (displayln "Hello")) ;; using this body

The problem I have is that "displayln" is highlighted with a blue-green 
background in DrRacket, indicating that it is provided by the module's 
language, but there is no arrow drawn from the "racket/base" just above.

If I change the last line of "MyLang.rkt" to put the fully-expanded module as a 
submodule (instead of merely extracting the contents of the 
#%plain-module-begin), then the arrow gets drawn:

#'(#%plain-module-begin (module nm lng (#%plain-module-begin . body)))

What conditions must be met for the arrow to be drawn?

[1] http://stackoverflow.com/a/38032107/324969

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Re: [racket-users] Language-provided bindings and arrows in DrRacket

[Alex Knauth]

> On Dec 4, 2016, at 10:27 AM, Dupéron Georges  
> wrote:
> 
> I think I found a solution which allows me to inject the (#%require lng) 
> without causing conflicts with other required module: applying an extra scope 
> to the whole body makes the other (require) forms more specific, and they can 
> shadow bindings imported by (#%require lng).

A nested scope seems like the correct solution. The macro expander does 
something similar with module body's, but it creates a pair of scopes for the 
body. I'm not sure whether you would need to do the same...

http://www.cs.utah.edu/plt/scope-sets/general-macros.html#%28part._.Modules_and_.Phases%29
 


I can't see any unwanted consequences of this approach, but I also don't know 
much about how scopes work with requires.

Alex Knauth

> Here is the modified "MyLang.rkt":
> 
> #lang racket
> (provide (rename-out [my-module-begin #%module-begin]))
> (define-syntax (my-module-begin stx)
>  (syntax-case stx ()
>[(_ real-lang body)
> (syntax-case (local-expand #'(module m real-lang body) 'top-level (list)) 
> ()
>   [(module nm lng (#%plain-module-begin . body2))
>#`(#%plain-module-begin
> (#%require lng)
> . #,((make-syntax-introducer) #'body2))])]))

> My problem seems solved, but if this extra-scope trick has some unwanted 
> consequences, I would definitely want to hear about them!


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