Re: [racket-users] Affecting the errors generated by syntax-parse

2015-07-25 Thread Stephen Chang 
I haven't played with the example in detail, but do you want the cut
operator here?

http://docs.racket-lang.org/syntax/stxparse-patterns.html?q=syntax-parse#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7e!%29%29

On Sat, Jul 25, 2015 at 9:55 AM, Jens Axel Søgaard
jensa...@soegaard.net wrote:
 Hi All,

 The syntax-parse form can often generate sensible errors based on the
 progress made
 during the attempt to match a pattern against a syntax-object. Given
 multiple choices
 the choice where the maximum progress was made is used to generate the
 error message.

 Is there a way to tell syntax-parse, that a given choice is to be used as
 the source
 of the error, if the match fails?

 A concrete example: In the toy language below a top-level form can be a
 definition
 or an expression. The malformed definition (define (foo 3) x) is not a legal
 definition -- it is however clear that the user intended to write a
 definition,
 since the form begins with (define ...). During matching syntax-parse
 makes more progress under the assumption that the definition is a sequence
 expression, so the error message becomes: begin expected.

 How can I stop the matching prematurely when the (define ...) is seen?

 /Jens Axel

 #lang racket
 ;;;
 ;;; URLANG
 ;;;

 ; In the grammar below x stands for a non-keyword identifier

 ; program::= top-level-form ...
 ; top-level-form ::= definition | expr

 ; definition ::= (define (x x ...) body)
 ; body   ::= expr

 ; expr   ::= datum | reference | application | sequence
 ; reference  ::= x
 ; application::= (x0 x ...)
 ; sequence   ::= (begin expr ...)

 ; keyword::= define | begin

 ; datum  ::= fixnum

 ; identifier an identifier that is not a keyword
 ; fixnum an integer between -2^53 and 2^53

 (require syntax/parse)

 (define min-fixnum (- (expt 2 53)))
 (define max-fixnum(expt 2 53))

 (define (Fixnum? r)
   (and (number? r) (integer? r)
(= min-fixnum r max-fixnum)))

 (define-syntax-class Fixnum
   #:opaque
   (pattern d
#:fail-unless (Fixnum? (syntax-e #'d)) #f))

 (define-syntax-class Datum
   (pattern (~or d:Fixnum)))

 (define-syntax-class Keyword
   #:literals (begin define)
   (pattern (~or begin define)))

 (define-syntax-class Id
   (pattern (~and x:id
  (~not y:Keyword

 (define-syntax-class Reference
   (pattern x:Id))

 (define-syntax-class Application
   #:literals (define)
   (pattern (e:Expr ...)))

 (define-syntax-class Sequence
   #:literals (begin)
   (pattern (begin e0:Expr e:Expr ...)))

 (define-syntax-class Definition
   #:literals (define)
   (pattern (define (name:Id a:Id ...) body:Body)))


 (define-syntax-class Body
   (pattern b:Expr))

 (define-syntax-class Expr
   (pattern (~or e:Datum
 e:Application
 e:Reference
 e:Sequence)))

 (define-syntax-class TopLevelForm
   (pattern (~or t:Definition
 t:Expr)))

 (define-syntax-class Program
   (pattern (p:TopLevelForm ...)))

 ;;; The following expressions show some legal
 ;;; constructs that are matched correctly.

 (syntax-parse #'3
   [d:Datum 'datum])

 (syntax-parse #'3
   [e:Expr 'expr])

 (syntax-parse #'(define (a x) x)
   [t:TopLevelForm 'toplevelform])

 (syntax-parse #'((define (foo x y) (+ x 1)) (foo 3))
   [p:Program 'program])

 ;;; The malformed definition (define (a 4 x) x) is
 ;;; correctly rejected as a toplevel form, but the
 ;;; automatically generated error is not as intended.

 (syntax-parse #'(define (a 4 x) x)
   [t:TopLevelForm 'toplevelform])

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[racket-users] Affecting the errors generated by syntax-parse

2015-07-25 Thread Jens Axel Søgaard 
Hi All,

The syntax-parse form can often generate sensible errors based on the
progress made
during the attempt to match a pattern against a syntax-object. Given
multiple choices
the choice where the maximum progress was made is used to generate the
error message.

Is there a way to tell syntax-parse, that a given choice is to be used as
the source
of the error, if the match fails?

A concrete example: In the toy language below a top-level form can be a
definition
or an expression. The malformed definition (define (foo 3) x) is not a legal
definition -- it is however clear that the user intended to write a
definition,
since the form begins with (define ...). During matching syntax-parse
makes more progress under the assumption that the definition is a sequence
expression, so the error message becomes: begin expected.

How can I stop the matching prematurely when the (define ...) is seen?

/Jens Axel

#lang racket
;;;
;;; URLANG
;;;

; In the grammar below x stands for a non-keyword identifier

; program::= top-level-form ...
; top-level-form ::= definition | expr

; definition ::= (define (x x ...) body)
; body   ::= expr

; expr   ::= datum | reference | application | sequence
; reference  ::= x
; application::= (x0 x ...)
; sequence   ::= (begin expr ...)

; keyword::= define | begin

; datum  ::= fixnum

; identifier an identifier that is not a keyword
; fixnum an integer between -2^53 and 2^53

(require syntax/parse)

(define min-fixnum (- (expt 2 53)))
(define max-fixnum(expt 2 53))

(define (Fixnum? r)
  (and (number? r) (integer? r)
   (= min-fixnum r max-fixnum)))

(define-syntax-class Fixnum
  #:opaque
  (pattern d
   #:fail-unless (Fixnum? (syntax-e #'d)) #f))

(define-syntax-class Datum
  (pattern (~or d:Fixnum)))

(define-syntax-class Keyword
  #:literals (begin define)
  (pattern (~or begin define)))

(define-syntax-class Id
  (pattern (~and x:id
 (~not y:Keyword

(define-syntax-class Reference
  (pattern x:Id))

(define-syntax-class Application
  #:literals (define)
  (pattern (e:Expr ...)))

(define-syntax-class Sequence
  #:literals (begin)
  (pattern (begin e0:Expr e:Expr ...)))

(define-syntax-class Definition
  #:literals (define)
  (pattern (define (name:Id a:Id ...) body:Body)))


(define-syntax-class Body
  (pattern b:Expr))

(define-syntax-class Expr
  (pattern (~or e:Datum
e:Application
e:Reference
e:Sequence)))

(define-syntax-class TopLevelForm
  (pattern (~or t:Definition
t:Expr)))

(define-syntax-class Program
  (pattern (p:TopLevelForm ...)))

;;; The following expressions show some legal
;;; constructs that are matched correctly.

(syntax-parse #'3
  [d:Datum 'datum])

(syntax-parse #'3
  [e:Expr 'expr])

(syntax-parse #'(define (a x) x)
  [t:TopLevelForm 'toplevelform])

(syntax-parse #'((define (foo x y) (+ x 1)) (foo 3))
  [p:Program 'program])

;;; The malformed definition (define (a 4 x) x) is
;;; correctly rejected as a toplevel form, but the
;;; automatically generated error is not as intended.

(syntax-parse #'(define (a 4 x) x)
  [t:TopLevelForm 'toplevelform])

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Re: [racket-users] Affecting the errors generated by syntax-parse

2015-07-25 Thread Jens Axel Søgaard 
Hi Stephen,

Thanks for testing this. Turns out I had removed a #:opaque in Definition
while cleaning up
the example before sending the mail. Now I get the same error as you.

With

(define-syntax-class Definition
  #:opaque
  #:literals (define)
  (pattern (define (name:Id a:Id ...) body:Body)))

I get the wrong error (because #:opaque shortens the progress).

I had experimented with ~! as in:

(define-syntax-class Definition
  #:opaque
  #:literals (define)
  (pattern (define ~! (name:Id a:Id ...) body:Body)))

but the #:opaque ruins the effect of ~! here (not sure why).


Sorry for the noise,
Jens Axel



2015-07-25 16:55 GMT+02:00 Stephen Chang stch...@ccs.neu.edu:

 Actually, I dont get the begin expected error that you mention. I'm
 getting:

 define: expected identifier
   parsing context:
while parsing Id
while parsing Definition
while parsing TopLevelForm in: 4

 with the 4 highlighted, which seems correct since it comes from using
 the Definition class?

 On Sat, Jul 25, 2015 at 10:51 AM, Stephen Chang stch...@ccs.neu.edu
 wrote:
  I haven't played with the example in detail, but do you want the cut
  operator here?
 
 
 http://docs.racket-lang.org/syntax/stxparse-patterns.html?q=syntax-parse#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7e!%29%29
 
  On Sat, Jul 25, 2015 at 9:55 AM, Jens Axel Søgaard
  jensa...@soegaard.net wrote:
  Hi All,
 
  The syntax-parse form can often generate sensible errors based on the
  progress made
  during the attempt to match a pattern against a syntax-object. Given
  multiple choices
  the choice where the maximum progress was made is used to generate the
  error message.
 
  Is there a way to tell syntax-parse, that a given choice is to be used
 as
  the source
  of the error, if the match fails?
 
  A concrete example: In the toy language below a top-level form can be a
  definition
  or an expression. The malformed definition (define (foo 3) x) is not a
 legal
  definition -- it is however clear that the user intended to write a
  definition,
  since the form begins with (define ...). During matching syntax-parse
  makes more progress under the assumption that the definition is a
 sequence
  expression, so the error message becomes: begin expected.
 
  How can I stop the matching prematurely when the (define ...) is seen?
 
  /Jens Axel
 
  #lang racket
  ;;;
  ;;; URLANG
  ;;;
 
  ; In the grammar below x stands for a non-keyword identifier
 
  ; program::= top-level-form ...
  ; top-level-form ::= definition | expr
 
  ; definition ::= (define (x x ...) body)
  ; body   ::= expr
 
  ; expr   ::= datum | reference | application |
 sequence
  ; reference  ::= x
  ; application::= (x0 x ...)
  ; sequence   ::= (begin expr ...)
 
  ; keyword::= define | begin
 
  ; datum  ::= fixnum
 
  ; identifier an identifier that is not a keyword
  ; fixnum an integer between -2^53 and 2^53
 
  (require syntax/parse)
 
  (define min-fixnum (- (expt 2 53)))
  (define max-fixnum(expt 2 53))
 
  (define (Fixnum? r)
(and (number? r) (integer? r)
 (= min-fixnum r max-fixnum)))
 
  (define-syntax-class Fixnum
#:opaque
(pattern d
 #:fail-unless (Fixnum? (syntax-e #'d)) #f))
 
  (define-syntax-class Datum
(pattern (~or d:Fixnum)))
 
  (define-syntax-class Keyword
#:literals (begin define)
(pattern (~or begin define)))
 
  (define-syntax-class Id
(pattern (~and x:id
   (~not y:Keyword
 
  (define-syntax-class Reference
(pattern x:Id))
 
  (define-syntax-class Application
#:literals (define)
(pattern (e:Expr ...)))
 
  (define-syntax-class Sequence
#:literals (begin)
(pattern (begin e0:Expr e:Expr ...)))
 
  (define-syntax-class Definition
#:literals (define)
(pattern (define (name:Id a:Id ...) body:Body)))
 
 
  (define-syntax-class Body
(pattern b:Expr))
 
  (define-syntax-class Expr
(pattern (~or e:Datum
  e:Application
  e:Reference
  e:Sequence)))
 
  (define-syntax-class TopLevelForm
(pattern (~or t:Definition
  t:Expr)))
 
  (define-syntax-class Program
(pattern (p:TopLevelForm ...)))
 
  ;;; The following expressions show some legal
  ;;; constructs that are matched correctly.
 
  (syntax-parse #'3
[d:Datum 'datum])
 
  (syntax-parse #'3
[e:Expr 'expr])
 
  (syntax-parse #'(define (a x) x)
[t:TopLevelForm 'toplevelform])
 
  (syntax-parse #'((define (foo x y) (+ x 1)) (foo 3))
[p:Program 'program])
 
  ;;; The malformed definition (define (a 4 x) x) is
  ;;; correctly rejected as a toplevel form, but the
  ;;; automatically generated error is not as intended.
 
  (syntax-parse #'(define (a 4 x) x)
[t:TopLevelForm 'toplevelform])
 
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 Groups
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Re: [racket-users] Affecting the errors generated by syntax-parse

2015-07-25 Thread Stephen Chang 
Actually, I dont get the begin expected error that you mention. I'm getting:

define: expected identifier
  parsing context:
   while parsing Id
   while parsing Definition
   while parsing TopLevelForm in: 4

with the 4 highlighted, which seems correct since it comes from using
the Definition class?

On Sat, Jul 25, 2015 at 10:51 AM, Stephen Chang stch...@ccs.neu.edu wrote:
 I haven't played with the example in detail, but do you want the cut
 operator here?

 http://docs.racket-lang.org/syntax/stxparse-patterns.html?q=syntax-parse#%28form._%28%28lib._syntax%2Fparse..rkt%29._~7e!%29%29

 On Sat, Jul 25, 2015 at 9:55 AM, Jens Axel Søgaard
 jensa...@soegaard.net wrote:
 Hi All,

 The syntax-parse form can often generate sensible errors based on the
 progress made
 during the attempt to match a pattern against a syntax-object. Given
 multiple choices
 the choice where the maximum progress was made is used to generate the
 error message.

 Is there a way to tell syntax-parse, that a given choice is to be used as
 the source
 of the error, if the match fails?

 A concrete example: In the toy language below a top-level form can be a
 definition
 or an expression. The malformed definition (define (foo 3) x) is not a legal
 definition -- it is however clear that the user intended to write a
 definition,
 since the form begins with (define ...). During matching syntax-parse
 makes more progress under the assumption that the definition is a sequence
 expression, so the error message becomes: begin expected.

 How can I stop the matching prematurely when the (define ...) is seen?

 /Jens Axel

 #lang racket
 ;;;
 ;;; URLANG
 ;;;

 ; In the grammar below x stands for a non-keyword identifier

 ; program::= top-level-form ...
 ; top-level-form ::= definition | expr

 ; definition ::= (define (x x ...) body)
 ; body   ::= expr

 ; expr   ::= datum | reference | application | sequence
 ; reference  ::= x
 ; application::= (x0 x ...)
 ; sequence   ::= (begin expr ...)

 ; keyword::= define | begin

 ; datum  ::= fixnum

 ; identifier an identifier that is not a keyword
 ; fixnum an integer between -2^53 and 2^53

 (require syntax/parse)

 (define min-fixnum (- (expt 2 53)))
 (define max-fixnum(expt 2 53))

 (define (Fixnum? r)
   (and (number? r) (integer? r)
(= min-fixnum r max-fixnum)))

 (define-syntax-class Fixnum
   #:opaque
   (pattern d
#:fail-unless (Fixnum? (syntax-e #'d)) #f))

 (define-syntax-class Datum
   (pattern (~or d:Fixnum)))

 (define-syntax-class Keyword
   #:literals (begin define)
   (pattern (~or begin define)))

 (define-syntax-class Id
   (pattern (~and x:id
  (~not y:Keyword

 (define-syntax-class Reference
   (pattern x:Id))

 (define-syntax-class Application
   #:literals (define)
   (pattern (e:Expr ...)))

 (define-syntax-class Sequence
   #:literals (begin)
   (pattern (begin e0:Expr e:Expr ...)))

 (define-syntax-class Definition
   #:literals (define)
   (pattern (define (name:Id a:Id ...) body:Body)))


 (define-syntax-class Body
   (pattern b:Expr))

 (define-syntax-class Expr
   (pattern (~or e:Datum
 e:Application
 e:Reference
 e:Sequence)))

 (define-syntax-class TopLevelForm
   (pattern (~or t:Definition
 t:Expr)))

 (define-syntax-class Program
   (pattern (p:TopLevelForm ...)))

 ;;; The following expressions show some legal
 ;;; constructs that are matched correctly.

 (syntax-parse #'3
   [d:Datum 'datum])

 (syntax-parse #'3
   [e:Expr 'expr])

 (syntax-parse #'(define (a x) x)
   [t:TopLevelForm 'toplevelform])

 (syntax-parse #'((define (foo x y) (+ x 1)) (foo 3))
   [p:Program 'program])

 ;;; The malformed definition (define (a 4 x) x) is
 ;;; correctly rejected as a toplevel form, but the
 ;;; automatically generated error is not as intended.

 (syntax-parse #'(define (a 4 x) x)
   [t:TopLevelForm 'toplevelform])

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