[racket] examples of hooking a #lang into DrRacket?

> It appears that read-language can return #f and what DrRacket does in
> that case appears to be what you're seeing. Is that what you're
> getting?

Your theory seems correct. Yes, Pollen is the only #lang returning #f for read-language, e.g.:

#lang racket/base
(map 
 (λ(lang) (read-language (open-input-string (format "#lang ~a" lang))))
    '(racket racket/base scratchy scribble/manual scribble/text rackjure pollen))

'(#<procedure:language-info>
  #<procedure:language-info>
  #<procedure:...atchy/reader.rkt:26:2>
  #<procedure:language-info>
  #<procedure:language-info>
  #<procedure:language-info>
  #f)


Moreover, if I use your main.rkt, it triggers the same problem in DrRacket (#lang line is red, no toolbar buttons)

But beyond the issue of whether the docs or DrRacket is doing the right thing with the #f value, I'm unclear why Pollen is returning #f for read-language. One possibly unorthodox thing I'm doing here is that my #lang files rely on macro expansion. For instance, here's Pollen's main.rkt:


#lang racket/base
(require pollen/main-base)
(define+provide-module-begin-in-mode world:mode-preproc)

(module reader racket/base
  (require pollen/reader-base)
  (define+provide-reader-in-mode world:mode-auto)) 


... where `define+provide-module-begin-in-mode` is a macro that creates the #%module-begin macro, and `define+provide-reader-in-mode` is a macro that creates the reader.

This doesn't bother DrRacket when the file is being run, but perhaps this approach is incompatible with either read-language, or DrRacket's #lang validation?





On Jul 20, 2014, at 4:50 PM, Robby Findler <robby at eecs.northwestern.edu> wrote:

> It appears that read-language can return #f and what DrRacket does in
> that case appears to be what you're seeing. Is that what you're
> getting?
> 
> The docs say that read-language never returns #f (presumably it is
> allowed to return #f when fail-thunk returns #f, but the relevant
> fail-thunk here doesn't return #f) so I'm not sure if that's a docs
> bug, in which case I should change drracket to cope with it or an
> implementation bug.
> 
> But if I create a pollen directory, use 'rack pkg --link pollen' to
> set it up and then put main.rkt with this content:
> 
> #lang racket/base
> (module reader racket/base (provide read-syntax)
>  (define (read-syntax a b)
>     #'(module m racket/base)))
> 
> then I see this:
> 
> $  racket
> Welcome to Racket v6.1.0.3.
>> (read-language (open-input-string "#lang pollen"))
> #f
> 
> 
> Robby