Re: [racket-users] stops in Macros that Work Together
Thanks for clearing that up Ryan Matthew :). -- Anthony Carrico -- You received this message because you are subscribed to the Google Groups Racket Users group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout. signature.asc Description: OpenPGP digital signature
[racket-users] stops in Macros that Work Together
I've been working through Macros that Work Together (on my way to
working through Sets-of-Scopes). I've come across something that is
slightly unclear to me in the section on local-expand:
E ::= a mapping from name to transform
I don't believe that E is a stack (right?). If it isn't, then in
jfp12-draft2-fcdf.pdf page 26:
nostops[E]={var-transform | E(var) = transform and transform != Stop}
Estops = nostops[E]+{resolve[idstop]-Stop} ...
This will clear out the stops of the outer macro and then install the
stops of the inner macro. My concern is that nostops does nothing to
reinstall the original transformers of the cleared stops. Shouldn't it?
--
Anthony Carrico
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Re: [racket-users] stops in Macros that Work Together
On 07/06/2015 10:04 PM, Anthony Carrico wrote:
I've been working through Macros that Work Together (on my way to
working through Sets-of-Scopes). I've come across something that is
slightly unclear to me in the section on local-expand:
E ::= a mapping from name to transform
I don't believe that E is a stack (right?). If it isn't, then in
jfp12-draft2-fcdf.pdf page 26:
nostops[E]={var-transform | E(var) = transform and transform != Stop}
Estops = nostops[E]+{resolve[idstop]-Stop} ...
This will clear out the stops of the outer macro and then install the
stops of the inner macro. My concern is that nostops does nothing to
reinstall the original transformers of the cleared stops. Shouldn't it?
If I remember correctly, nostops does in fact depend on the definition
of environments as alists, so when the Stop binding is removed, the
previous binding becomes visible again. You can get the actual redex
models behind the paper here:
http://www.cs.utah.edu/plt/expmodel-6/
Ryan
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Re: [racket-users] stops in Macros that Work Together
At Mon, 06 Jul 2015 23:24:20 -0400, Ryan Culpepper wrote:
On 07/06/2015 10:04 PM, Anthony Carrico wrote:
I've been working through Macros that Work Together (on my way to
working through Sets-of-Scopes). I've come across something that is
slightly unclear to me in the section on local-expand:
E ::= a mapping from name to transform
I don't believe that E is a stack (right?). If it isn't, then in
jfp12-draft2-fcdf.pdf page 26:
nostops[E]={var-transform | E(var) = transform and transform != Stop}
Estops = nostops[E]+{resolve[idstop]-Stop} ...
This will clear out the stops of the outer macro and then install the
stops of the inner macro. My concern is that nostops does nothing to
reinstall the original transformers of the cleared stops. Shouldn't it?
If I remember correctly, nostops does in fact depend on the definition
of environments as alists, so when the Stop binding is removed, the
previous binding becomes visible again. You can get the actual redex
models behind the paper here:
http://www.cs.utah.edu/plt/expmodel-6/
(And that demonstrates a hazard of providing a custom typesetting rule
with Redex!)
In case it's useful, the set-of-scopes model avoids this mistake by
having `Stop` record the previous transformer value. Then, the `unstop`
metafunction (instead of `nostops`) can restore it:
http://www.cs.utah.edu/~mflatt/scope-sets-5/model.html#%28part._.Local_.Expansion%29
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