[racket] prefix/rename for signatures in unit and define-signature forms

I think the problem is with `process-import/export` in
"collects/racket/private/unit-compiletime.rkt".

If you change

  (do-prefix (add-prefix id) #'pid)

to

  (add-prefix (do-prefix id #'pid))

then it looks like the tests still pass, and your examples work more as
expected. I'm not sure it's as simple as that; can you take a closer
look there?

At Fri, 9 May 2014 16:39:34 -0400 (EDT), dfeltey at ccs.neu.edu wrote:
> I've been digging in to this some more, and it seems that the prefix form works 
> backwards on a sig-spec, for example:
> 
> (define-signature a^ (a))
> (define-signature dcc^ ((open (prefix d: (prefix c: (prefix c: a^))))))
> (define d@ (unit (import dcc^) (export) c:c:d:a))
> 
> (unit (import)
>       (export (prefix d: (prefix c: (prefix c: a^))))
>       (define c:c:d:a 5))
> 
> This makes some sort of sense, I suppose, but it doesn't really match what the 
> docs seem to say.
> 
> On the other hand rename does seem to work in expected way when used by itself:
> 
> (define-signature da^
>   ((open (rename (rename (rename a^ (b a)) (c b)) (d c)))))
> (unit (import da^) (export) d)
> (unit (import (rename (rename (rename a^ (b a)) (c b)) (d c))) (export) d)
> 
> When I try to nest different combinations of rename and prefix together, 
> however, I get the strange behavior I was experiencing yesterday, and I cannot 
> figure out how to correctly reason about what the resulting bindings should be.
> 
> Thanks
> Dan
> 
> 
> ----- Original Message -----
> From: dfeltey at ccs.neu.edu
> To: users at racket-lang.org
> Sent: Thursday, May 8, 2014 4:56:52 PM GMT -05:00 US/Canada Eastern
> Subject: [racket] prefix/rename for signatures in unit and define-signature 
> forms
> 
> I'm trying to make sense of how prefix/rename work for signatures, but in 
> trying to run some examples the actual implementation doesn't seem to match 
> either my intuition or the documentation. 
> 
> For example I have the following simple signature:
> 
> (define-signature a^ (a))
> 
> I then try to build a new signature from a^ with a combination of open and 
> prefix/rename.
> 
> (define-signature b-bad^
>   ((open (prefix x: (rename (prefix y: a^) (q y:a))))))
> 
> This example, however, gives the error: 
> "open: listed identifier not present in signature specification in: x:y:a"
> 
> I'm not sure I understand this since it appears as though prefixing x: comes 
> before the renaming, but I would have though that first y: is prefixed to a, so 
> that y:a is in the signature which can then be renamed q. So in the end the 
> only variable in the signature should be x:q.
> 
> Attempting the same in a unit form gives a similar error:
> 
> (define u-bad 
>   (unit (import (prefix x: (rename (prefix y: a^) (q y:a)))) 
>         (export)
>         x:q))
> "unit: listed identifier not present in signature specification in: x:y:a"
> 
> 
> If I change the prefix x: to y: things seem to work for some reason.
> 
> (define-signature b-good^
>   ((open (prefix y: (rename (prefix y: a^) (q y:a))))))
> 
> In this case, I still expect the variable in the signature to be something like 
> y:q, but trying a similar renaming in a unit form fails:
> 
> (define u-bad2 
>   (unit (import (prefix y: (rename (prefix y: a^) (q y:a)))) 
>         (export)
>         y:q))
> 
> With the error:
> "y:q: unbound identifier in module in: y:q"
> 
>  while the following does work
> 
> (define u-good 
>   (unit (import (prefix y: (rename (prefix y: a^) (q y:a)))) 
>         (export)
>         q))
> 
> 
> Am I misunderstanding something obvious about the way that the 
> renaming/prefixing should be taking place on the level of a signature or unit 
> import/export clause? The results I'm seeing are completely unintuitive to me 
> and the documentation doesn't seem to clarify this for me.
> 
> Thanks
> Dan
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