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Is it possible to change the result of a syntax-class?

define-match-expanderWhen should I use syntax/loc instead of #' (aka syntax)?How can I group optional attributes captured with syntax-parse?Use a syntax list as formal parameters to a functionDefining a nested racket macro with access to surrounding variablesA splicing syntax class that matches an optional pattern and binds attributesracket - define-syntax-class with pattern matching procedureread-syntax: `#…=` forms not enabledsyntax for unsyntax in syntax-parseHow to access syntax-class attributes in `~optional` that contains ellipsis?

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3

I currently have a bunch of splicing syntax classes I use to generate code.

They look like this:

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y)
 #:with result #'(vec x y)))

The goal is to be able to match a sequence x y anywhere and replace it with (vec x y).

The only way I see for now is by creating an attribute called result and use it:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>.result)])
#'(vec 4.2 5.7)

Is there a way to change my code so that I can get the same result by writing the following?

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>)])
#'(4.2 5.7) ;; not what I want

racket

share|improve this question

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

add a comment | 

3

I currently have a bunch of splicing syntax classes I use to generate code.

They look like this:

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y)
 #:with result #'(vec x y)))

The goal is to be able to match a sequence x y anywhere and replace it with (vec x y).

The only way I see for now is by creating an attribute called result and use it:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>.result)])
#'(vec 4.2 5.7)

Is there a way to change my code so that I can get the same result by writing the following?

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>)])
#'(4.2 5.7) ;; not what I want

racket

share|improve this question

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

add a comment | 

I currently have a bunch of splicing syntax classes I use to generate code.

They look like this:

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y)
 #:with result #'(vec x y)))

The goal is to be able to match a sequence x y anywhere and replace it with (vec x y).

The only way I see for now is by creating an attribute called result and use it:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>.result)])
#'(vec 4.2 5.7)

Is there a way to change my code so that I can get the same result by writing the following?

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>)])
#'(4.2 5.7) ;; not what I want

racket

share|improve this question

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y)
 #:with result #'(vec x y)))

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>.result)])
#'(vec 4.2 5.7)

> (syntax-parse #'(position 4.2 5.7)
 [(<name> <pos>:vec-exp)
 (attribute <pos>)])
#'(4.2 5.7) ;; not what I want

share|improve this question

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

share|improve this question

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

asked Mar 27 at 15:25

Jérôme MartinJérôme Martin

1,04211 gold badge1111 silver badges2424 bronze badges

2 Answers
2

active

oldest

votes

2

FWIW, you can do this. Not sure if it's acceptable for you or not.

(require syntax/parse
 (for-syntax syntax/parse))

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y) #:with result #'(vec x y)))

(define-syntax ~res
 (pattern-expander
 (syntax-parser
 [(_ pat cls)
 #'(~and (~var PAT cls) (~bind [pat (attribute PAT.result)]))])))

And then:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> (~res <pos> vec-exp))
 (attribute <pos>)])
#'(vec 4.2 5.7)

share|improve this answer

edited Apr 30 at 8:26

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Really nice trick, thanks!
  
  – Jérôme Martin
  Apr 30 at 8:12
  

  
  
  
  

add a comment | 

1

I don't think so. The pattern (<name> <pos>:vec-exp) means "The input must be a list; bind its elements to pattern variables <name> and <pos>." Those pattern variables provide access to what got matched. The attributes returned by the syntax class are what got generated. The syntax-parse system is very fastidious about keeping those two concepts distinct, so I don't think it will let you replace one with the other.

Are you trying to make your macro more readable or less error-prone? If so, maybe tell us a little more. Maybe there is a way to do that.

share|improve this answer

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

add a comment | 

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2

FWIW, you can do this. Not sure if it's acceptable for you or not.

(require syntax/parse
 (for-syntax syntax/parse))

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y) #:with result #'(vec x y)))

(define-syntax ~res
 (pattern-expander
 (syntax-parser
 [(_ pat cls)
 #'(~and (~var PAT cls) (~bind [pat (attribute PAT.result)]))])))

And then:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> (~res <pos> vec-exp))
 (attribute <pos>)])
#'(vec 4.2 5.7)

share|improve this answer

edited Apr 30 at 8:26

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Really nice trick, thanks!
  
  – Jérôme Martin
  Apr 30 at 8:12
  

  
  
  
  

add a comment | 

2

FWIW, you can do this. Not sure if it's acceptable for you or not.

(require syntax/parse
 (for-syntax syntax/parse))

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y) #:with result #'(vec x y)))

(define-syntax ~res
 (pattern-expander
 (syntax-parser
 [(_ pat cls)
 #'(~and (~var PAT cls) (~bind [pat (attribute PAT.result)]))])))

And then:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> (~res <pos> vec-exp))
 (attribute <pos>)])
#'(vec 4.2 5.7)

share|improve this answer

edited Apr 30 at 8:26

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Really nice trick, thanks!
  
  – Jérôme Martin
  Apr 30 at 8:12
  

  
  
  
  

add a comment | 

FWIW, you can do this. Not sure if it's acceptable for you or not.

(require syntax/parse
 (for-syntax syntax/parse))

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y) #:with result #'(vec x y)))

(define-syntax ~res
 (pattern-expander
 (syntax-parser
 [(_ pat cls)
 #'(~and (~var PAT cls) (~bind [pat (attribute PAT.result)]))])))

And then:

> (syntax-parse #'(position 4.2 5.7)
 [(<name> (~res <pos> vec-exp))
 (attribute <pos>)])
#'(vec 4.2 5.7)

share|improve this answer

edited Apr 30 at 8:26

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

(require syntax/parse
 (for-syntax syntax/parse))

(define-splicing-syntax-class vec-exp
 (pattern (~seq x y) #:with result #'(vec x y)))

(define-syntax ~res
 (pattern-expander
 (syntax-parser
 [(_ pat cls)
 #'(~and (~var PAT cls) (~bind [pat (attribute PAT.result)]))])))

> (syntax-parse #'(position 4.2 5.7)
 [(<name> (~res <pos> vec-exp))
 (attribute <pos>)])
#'(vec 4.2 5.7)

share|improve this answer

edited Apr 30 at 8:26

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

answered Apr 29 at 10:11

Sorawee PorncharoenwaseSorawee Porncharoenwase

2,54599 silver badges2121 bronze badges

1

I don't think so. The pattern (<name> <pos>:vec-exp) means "The input must be a list; bind its elements to pattern variables <name> and <pos>." Those pattern variables provide access to what got matched. The attributes returned by the syntax class are what got generated. The syntax-parse system is very fastidious about keeping those two concepts distinct, so I don't think it will let you replace one with the other.

Are you trying to make your macro more readable or less error-prone? If so, maybe tell us a little more. Maybe there is a way to do that.

share|improve this answer

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

add a comment | 

1

I don't think so. The pattern (<name> <pos>:vec-exp) means "The input must be a list; bind its elements to pattern variables <name> and <pos>." Those pattern variables provide access to what got matched. The attributes returned by the syntax class are what got generated. The syntax-parse system is very fastidious about keeping those two concepts distinct, so I don't think it will let you replace one with the other.

Are you trying to make your macro more readable or less error-prone? If so, maybe tell us a little more. Maybe there is a way to do that.

share|improve this answer

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

add a comment | 

I don't think so. The pattern (<name> <pos>:vec-exp) means "The input must be a list; bind its elements to pattern variables <name> and <pos>." Those pattern variables provide access to what got matched. The attributes returned by the syntax class are what got generated. The syntax-parse system is very fastidious about keeping those two concepts distinct, so I don't think it will let you replace one with the other.

Are you trying to make your macro more readable or less error-prone? If so, maybe tell us a little more. Maybe there is a way to do that.

share|improve this answer

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

share|improve this answer

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges

answered Apr 8 at 18:52

Ben KovitzBen Kovitz

2,54511 gold badge1414 silver badges3838 bronze badges