Re: [racket-dev] syntax property duplication
On Sep 6, 2011, at 8:12 PM, Sam Tobin-Hochstadt wrote: On Tue, Sep 6, 2011 at 8:05 PM, John Clements cleme...@brinckerhoff.org wrote: On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. Would syntax-property guards solve this problem? I don't really see how. What are you thinking of? A guard could keep track of duplicates. Keep in mind that syntax-property guards are purely a figment of my imagination. John smime.p7s Description: S/MIME cryptographic signature _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Wed, Sep 7, 2011 at 1:37 PM, John Clements cleme...@brinckerhoff.org wrote: On Sep 6, 2011, at 8:12 PM, Sam Tobin-Hochstadt wrote: On Tue, Sep 6, 2011 at 8:05 PM, John Clements cleme...@brinckerhoff.org wrote: On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. Would syntax-property guards solve this problem? I don't really see how. What are you thinking of? A guard could keep track of duplicates. Keep in mind that syntax-property guards are purely a figment of my imagination. What, in your imagination, is a syntax-property guard? --Carl _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Sep 7, 2011, at 10:40 AM, Carl Eastlund wrote: On Wed, Sep 7, 2011 at 1:37 PM, John Clements cleme...@brinckerhoff.org wrote: On Sep 6, 2011, at 8:12 PM, Sam Tobin-Hochstadt wrote: On Tue, Sep 6, 2011 at 8:05 PM, John Clements cleme...@brinckerhoff.org wrote: On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. Would syntax-property guards solve this problem? I don't really see how. What are you thinking of? A guard could keep track of duplicates. Keep in mind that syntax-property guards are purely a figment of my imagination. What, in your imagination, is a syntax-property guard? I imagine that when the key involved in the property is a special guarded-syntax-property value, then an associated procedure gets to decide (approve/reject, substitute an alternate value?) whether a value should be used. If I understand the problem, the obvious danger in an idea such as this is opening a back door into expansion time. Apologies if I've misunderstood the issue. John smime.p7s Description: S/MIME cryptographic signature _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. Would syntax-property guards solve this problem? John smime.p7s Description: S/MIME cryptographic signature _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Tue, Sep 6, 2011 at 8:05 PM, John Clements cleme...@brinckerhoff.org wrote: On Aug 18, 2011, at 5:32 AM, Sam Tobin-Hochstadt wrote: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. Would syntax-property guards solve this problem? I don't really see how. What are you thinking of? -- sam th sa...@ccs.neu.edu _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Wed, Aug 17, 2011 at 6:25 PM, Sam Tobin-Hochstadt sa...@ccs.neu.edu wrote: The following idiom duplicates the syntax properties on `stx': (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) This is a problem for me because I use syntax properties to indicate polymorphic type instantiation. If an expression that's actually a macro using this idiom is instatiated, then Typed Racket tries to do the type instantiation twice, resulting in an error. See the below program, which fails. Should I expect that duplicate syntax properties are a natural result of expansion, and find some way to handle them? Or is there something else that should happen? #lang typed/racket (: id : (All (A) (A - A))) (define (id x) x) (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) (inst m Integer) -- sam th sa...@ccs.neu.edu Merging syntax properties -- duplicating in this case, since the macro's input and output have the same properties -- are a natural result of expansion, as you say. See the third paragraph in the reference on syntax properties: http://docs.racket-lang.org/reference/stxprops.html I think you need to find some way to handle them. --Carl _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
Re: [racket-dev] syntax property duplication
On Thu, Aug 18, 2011 at 8:14 AM, Carl Eastlund c...@ccs.neu.edu wrote: On Wed, Aug 17, 2011 at 6:25 PM, Sam Tobin-Hochstadt sa...@ccs.neu.edu wrote: The following idiom duplicates the syntax properties on `stx': (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) This is a problem for me because I use syntax properties to indicate polymorphic type instantiation. If an expression that's actually a macro using this idiom is instatiated, then Typed Racket tries to do the type instantiation twice, resulting in an error. See the below program, which fails. Should I expect that duplicate syntax properties are a natural result of expansion, and find some way to handle them? Or is there something else that should happen? #lang typed/racket (: id : (All (A) (A - A))) (define (id x) x) (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) (inst m Integer) Merging syntax properties -- duplicating in this case, since the macro's input and output have the same properties -- are a natural result of expansion, as you say. See the third paragraph in the reference on syntax properties: Yes, I understand why this happens. As I see it, there are a few possibilities: 1. The expander should check for duplicates, in some fashion. 2. This idiom is problematic, in the case where `stx' is both the input and used for the syntax properties of the output. 3. Macros may freely duplicate syntax properties. All of these have drawbacks, but (3), which you are suggesting, means either that syntax properties can only be used to specify idempotent information or that the non-idempotent ones need to have some *explicit* means by which equal elements can be distinguished, which must be part of the API of that syntax property. If we think this is how syntax properties ought to work, then we should add something to the documentation making this clear, and we should recognize that it's a limitation. -- sam th sa...@ccs.neu.edu _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
[racket-dev] syntax property duplication
The following idiom duplicates the syntax properties on `stx': (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) This is a problem for me because I use syntax properties to indicate polymorphic type instantiation. If an expression that's actually a macro using this idiom is instatiated, then Typed Racket tries to do the type instantiation twice, resulting in an error. See the below program, which fails. Should I expect that duplicate syntax properties are a natural result of expansion, and find some way to handle them? Or is there something else that should happen? #lang typed/racket (: id : (All (A) (A - A))) (define (id x) x) (define-syntax (m stx) (datum-syntax #'here 'id stx stx)) (inst m Integer) -- sam th sa...@ccs.neu.edu _ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
