[racket-dev] define #lang and use in same file (+ some funny behavior)

Ah, thanks! I somehow missed the existence of the submod form.



On Mon, Dec 3, 2012 at 4:44 PM, Carl Eastlund <cce at ccs.neu.edu> wrote:
> You can't define the reader part of a #lang in the same file and then use
> it, but you can definitely define the bindings, from things like
> #%module-begin and #%app on up, and use it in the same file.  The following
> works fine for me:
>
> #lang racket
>
> (module greeting racket
>   (provide #%module-begin)
>   (require (for-syntax syntax/parse))
>   (define-syntax #%module-begin
>     (syntax-parser
>       [(_ one:str two:str)
>        #'(#%plain-module-begin
>            (printf "Hello, ~a!\n" 'one)
>            (printf "Salutations, ~a!\n" 'two))])))
>
> (module main (submod ".." greeting)
>   "Santa Claus"
>   "Easter Bunny")
>
>
> Carl Eastlund
>
>
> On Mon, Dec 3, 2012 at 3:46 PM, Stephen Chang <stchang at ccs.neu.edu> wrote:
>>
>> When doing quick experiments, I've often wanted the ability to define
>> a new language and then use it in the same file. I thought submodules
>> might allow me to do this, but I've realized that I still can't.
>> However, in trying to do so I ran into some interesting behavior:
>>
>>
>> Here is a file named test.rkt that is saved to disk:
>>
>>     #lang racket
>>
>>     (define-syntax-rule (app x ...) (begin (displayln "hello") (#%app x
>> ...)))
>>
>>     (provide (except-out (all-from-out racket) #%app)
>>              (rename-out [app #%app]))
>>
>>
>> If I then add to the same file:
>>
>>     (module test "test.rkt" (+ 1 2))
>>
>> but *don't* save, pressing run in drracket displays:
>>
>> Welcome to DrRacket, version 5.3.1.1 [3m].
>> Language: racket [custom].
>> hello
>> 3
>> >
>>
>>
>> Then if I save and run again, I get an error:
>>
>> Welcome to DrRacket, version 5.3.1.1 [3m].
>> Language: racket [custom].
>> . . ../plt/collects/compiler/cm.rkt:350:0:
>> standard-module-name-resolver: cycle in loading
>>   at path: /home/stchang/tmp/test.rkt
>>   paths:
>>    /home/stchang/tmp/test.rkt
>> >
>>
>>
>> Is this the intended behavior? I guess this is what I would expect but
>> it feels funny since an identical buffer produces different output
>> depending on it's saved status.
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>