Embedded racket (cs) question

[Nate Griswold]

Hello.

I noticed something and was wondering what the list thinks:

I am using an embedded racket Ics) and i noticed that if i embed a file and don't include any libraries (for a very bare bones c file) i have problems with a crash on a promise on any dynamic-require:

build-path: contract violation
  expected: (or/c path-string? path-for-some-system? 'up 'same)
  given: #<promise:config:installation-name>

but if i do a (require racket/promise) in my rkt argument to --c-mods OR if i do a ++lib racket/promise i get no crash.

So is this expected behavior? Should racket/promise always be included or no? And what exactly is going on under the hood here?

Nate

[Sam Tobin-Hochstadt]

My guess, not having looked further than your email, is that when you don't include racket/promise, something is supplying a promise to something else but there are two different instantiations of the promise library, causing the force call from one not to recognize the promise from the other. Then force just becomes the identity function, and passes through a promise to somewhere that isn't expecting one.  

Is it possible that some library you're using features promises? Alternatively, it might be that the embedding code needs an explicit dependency on promises. 

Sam

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[Nate Griswold]

Sam, thanks

To be clear, this crash happened DURING a dynamic-require and judging by the stack trace looked to be part of the dynamic-require machinery (and this seems to depend on the installation name).

I actually wasn't depending on anything but racket/base, so i don't believe anything i was using was causing a separate dependency on promise.

Nate

[Matthew Flatt]

I'm not sure how it could be in `dynamic-require` itself, as opposed to
a library that is loaded by `dynamic-require`, but it sounds like a bug
at some level. Can you provide a small example?

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[Ryan Culpepper]

I don't know if it helps, but config:installation-name is a promise defined by setup/private/dirs.

Ryan

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[Nate Griswold]

I put up a repo with the bug at https://github.com/nwg/racket-expo

The stack trace is this:

build-path: contract violation
  expected: (or/c path-string? path-for-some-system? 'up 'same)
  given: #<promise:config:installation-name>

  context...:
   do-raise-argument-error
   loop
   build
   proc
   call-in-empty-metacontinuation-frame
   call-with-module-prompt
   body of "/Applications/Racket v7.7/collects/planet/config.rkt"
   temp35_0
   for-loop
   run-module-instance!
   for-loop
   [repeats 1 more time]
   run-module-instance!
   for-loop
   [repeats 1 more time]
   run-module-instance!

Nate

[Matthew Flatt]

Thanks for the example! I did not guess correctly about your mixture of
embedded modules and `dynamic-require`.

The short answer is that you should either embed modules or reference
them through an external paths like "/Applications/Racket
v7.7/collects", but not both. Otherwise, the two worlds collide in
confusing ways, in this case along the lines Sam suggested.


Longer answer: When you embed a module, it pulls along a copy of
anything that module depends on. Your "test.rkt" pulls along
`racket/base`, which pulls along `racket/private/promise`, which
defines `force` and the promise datatype. But it doesn't
`racket/promise`, which defines `delay/sync`, and that leads to a
mismatch.


Very long answer: When `server` starts, there are two possible
`racket/private/promise`s available: the emebded copy and the one in
"/Applications/Racket v7.7/collects". As an artifact of the way that
`racket/promise` references `racket/private/promise`, the
`racket/promise` in "/Applications/Racket v7.7/collects" will always
refer to the `racket/private/promise` there. And so `delay/sync` as
used in `setup/private/dirs` will refer to the promise datatype there.
But the `force` used in `setup/private/dirs` goes through `racket/base`
and ends up referring the the embedded `racket/private/promise`, which
has its own promise datatype; since `force` doesn't recognize the
result of `delay/sync` as a promise, it doesn't force the (othe rkind
of) promise, and it instead just returns it. Finally, `planet/config`
is unhappy to get back a promise, because it expects a path.


If you expect a full "collects" directory and more to be around at run
time, then there's no reason to embed code, and just use

racket_dynamic_require(Sstring("test.rkt"), Sfalse);

to load the module. But if you want to embed everything, then avoid
`dynamic-require` or use `++lib` or `define-module-path-index` to carry
along the dynamically required modules.


Matthew

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[Nate Griswold]

Great, thanks for all of that digging. Ya, i think i will go the non-declare_modules, non-ctool route for now as i think this fits my use-case pretty well. I want to allow access to the full racket library for racket code that changes often.

Nate