Re: [racket-users] Is there a way to eval a custom language from inside a module... without instantiating modules multiple times?

[Andrew Wilcox]

>
> 2. Just use the same namespace as eval-example.rkt 
>
 
I had tried this, but it evals not just the example language but 
Racket+example (i.e. Racket forms also eval, and the example language has 
to be compatible with Racket).

1. Keep the new namespace, but use namespace-attach-module to attach 
> runtime.rkt from eval-example.rkt to example-namespace before 
> (namespace-require example). 
>
 
That worked!  I'm now able to define a struct in my runtime library, and it 
ends up being the same struct type in both modules.  Thank you!

You've mentioned that you want to "define a custom language" and evaluate 
> it. But so far I don't see any sign that you're using Racket's dedicated 
> facilities for doing this (especially `#%module-begin` and `module`). If 
> this is a deliberate choice, carry on. If not, consider investigating them, 
> because they streamline the very chores you're finding painful.


Yes, I understand :-)

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Re: [racket-users] Is there a way to eval a custom language from inside a module... without instantiating modules multiple times?

[Matthew Butterick]

You've mentioned that you want to "define a custom language" and evaluate it. 
But so far I don't see any sign that you're using Racket's dedicated facilities 
for doing this (especially `#%module-begin` and `module`). If this is a 
deliberate choice, carry on. If not, consider investigating them, because they 
streamline the very chores you're finding painful.


> On Nov 16, 2018, at 10:43 AM, Andrew Wilcox  wrote:
> 
> What I want to do is rather simple (I hope): define a custom language in a 
> module such as example.rkt, and then be able to eval that language.
> 
> Is there a way to do this?



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Re: [racket-users] Is there a way to eval a custom language from inside a module... without instantiating modules multiple times?

[Shu-Hung You]

On Fri, Nov 16, 2018 at 12:43 PM Andrew Wilcox  wrote:
>
> I'd like to be able to eval a custom language from inside a module... without 
> instantiating modules multiple times.
>
> With the help of Matthew Butterick, I've gotten this far:
>
> ; runtime.rkt
> #lang racket
>
>
> (printf "This is runtime.rkt~n")
>
>
>
> ; example.rkt
> #lang racket
>
> (require "runtime.rkt")
>
> (provide foo)
>
> (printf "This is example.rkt~n")
>
> (define-syntax foo
>   (syntax-rules ()
> ((foo)
>  (printf "foo!~n"
>
>
>
> ; eval-example.rkt
> #lang racket
>
> (require racket/runtime-path)
>
> (require "runtime.rkt")
>
> (provide eval-example)
>
> (define-runtime-path example "example.rkt")
>
> (define example-namespace (make-base-empty-namespace))
>
> (parameterize ((current-namespace example-namespace))
>   (namespace-require example))
>
> (define (eval-example code)
>   (parameterize ((current-namespace example-namespace))
> (eval code)))
>
>
> however this instantiates runtime.rkt twice:
>
> $ racket eval-example.rkt
> This is runtime.rkt
> This is runtime.rkt
> This is example.rkt
>
>
> which turns out to be bad (for example, if I define a struct in the runtime, 
> I end up having a different struct types).  I want there to be a single copy 
> of the runtime.rkt module (much like if I had said (require "runtime.rkt") 
> from two different modules).
>
> What I want to do is rather simple (I hope): define a custom language in a 
> module such as example.rkt, and then be able to eval that language.
>
> Is there a way to do this?
>

Because eval-example.rkt creates a new, independent namespace and runs
example.rkt in the new namespace, the modules eval-example.rkt and
example.rkt will have different instantiations of runtime.rkt. The
workaround, therefore, is to share the instantiation of runtime.rkt.
However, sharing also implies that eval-example.rkt could be affected
by example.rkt unexpectedly.

There are two ways to share the instantiation of runtime.rkt.

1. Keep the new namespace, but use namespace-attach-module to attach
runtime.rkt from eval-example.rkt to example-namespace before
(namespace-require example).

;; eval-example.rkt
> (define-runtime-module-path runtime "runtime.rkt")
> (define-namespace-anchor here)
> (define host (namespace-anchor->namespace here))
> (parameterize ((current-namespace example-namespace))
>   (namespace-attach-module host runtime)
>   (namespace-require example))

2. Just use the same namespace as eval-example.rkt

;; eval-example.rkt
> (define-namespace-anchor here)
> (define example-namespace (namespace-anchor->namespace here))

Both methods need to be used with care.

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