Re: [racket-users] Trying to build 'routing' macro for dispatch-rules

[Jay McCarthy]

Hi David,

The syntax of `dispatch-rules` is that its arguments are dispatch
clauses, not expressions, and it does not implement its own macro
system (like `match` does.)

You should either change `dispatch-rules` to do that by adding
"dispatch-rules-expanders" or make your own macro to expand into a
call to `dispatch-rules`

Jay

On Fri, Oct 28, 2016 at 2:49 PM, David Storrs  wrote:
> I'm trying to build a macro that will generate routing rules for
> 'dispatch-rules'.
>
> (dispatch-rules) from web-server/dispatch has this form:
>
> (dispatch-rules
>(("announce-user") #:method post process-announce-user))
>...more routes here...
> )
>
> This seems like it should be automatable, so I tried to write a macro
> to generate these rules.  I'd like
> (routing announce-user)
> to expand to the line above:(("announce-user") #:method post
> process-announce-user))
>
> Here's my stab at it, which is currently failing:
>
>
> ;;This part works if I use it directly, ie:
> ;;  [("announce-file") #:method post (make-route msg-announce-file
> announce-file*)]
> ;;
> (define (make-route msg-handler pbuf-type)
>   (lambda (req)
> (msg-handler (req->protobuf req pbuf-type
>
>
> ;;Let's try to generate the entire rule using the above
> (define-syntax (routing stx)
>   (syntax-case
>   stx ()
> ([_ pbuf-type]
>  (with-syntax* ([type-name(format-id stx "~a*" #'pbuf-type)]
> [handler-name (format-id stx "msg-~a" #'type-name)]
> [route-name   (symbol->string (syntax->datum
> (format-id stx "~a" (syntax->datum #'pbuf-type]
> )
>#'[(route-name) #:method "post" (make-route
> handler-name type-name)]
> ;;   #'(quote [(route-name) #:method "post"
> (make-route handler-name type-name)])
>
>
> ;;(routing announce-file)  ; If I use this (i.e. outside the
> dispatch-rules) in combination with the 'quote' version above, I see
> the correct thing
>
> (define-values (dispatch-request url-for)
>   (dispatch-rules
>(routing announce-file)
>[("create-user") #:method post process-create-user]
>...more routes here...
> )
>
> Error is:
>
> racket network/routing.rkt
> ~/app/network/routing.rkt:194.2: dispatch-rules: bad syntax
>   in: (dispatch-rules (routing announce-file) (("create-user")
> #:method post process-create-user) ...
>   context...:
>
> /Applications/Racket_v6.6/collects/syntax/parse/private/runtime-report.rkt:698:0:
> error/report
>
> /Applications/Racket_v6.6/collects/syntax/parse/private/runtime-report.rkt:28:0:
> call-current-failure-handler
>standard-module-name-resolver
>
>
> As mentioned in the comments, it does generate (the quoted form of)
> the correct thing if I:
>
> 1) inside the macro, comment in the 'quote' line and comment out the
> line above it
> 2) comment OUT the '(routing announce-file) that is inside dispatch-rules
> 3) comment IN the (routing announce-user) line that is just above 
> dispatch-rules
>
>
> My suspicion is that dispatch-rules is a macro and so my macro is not
> being expanded inside another macro.  That's not how I thought macros
> worked, though, so now I'm really puzzled.
>
> Can anyone clarify this for me?
>
> --
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-- 
Jay McCarthy
Associate Professor
PLT @ CS @ UMass Lowell
http://jeapostrophe.github.io

   "Wherefore, be not weary in well-doing,
  for ye are laying the foundation of a great work.
And out of small things proceedeth that which is great."
  - D 64:33

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[racket-users] Trying to build 'routing' macro for dispatch-rules

[David Storrs]

I'm trying to build a macro that will generate routing rules for
'dispatch-rules'.

(dispatch-rules) from web-server/dispatch has this form:

(dispatch-rules
   (("announce-user") #:method post process-announce-user))
   ...more routes here...
)

This seems like it should be automatable, so I tried to write a macro
to generate these rules.  I'd like
(routing announce-user)
to expand to the line above:(("announce-user") #:method post
process-announce-user))

Here's my stab at it, which is currently failing:


;;This part works if I use it directly, ie:
;;  [("announce-file") #:method post (make-route msg-announce-file
announce-file*)]
;;
(define (make-route msg-handler pbuf-type)
  (lambda (req)
(msg-handler (req->protobuf req pbuf-type


;;Let's try to generate the entire rule using the above
(define-syntax (routing stx)
  (syntax-case
  stx ()
([_ pbuf-type]
 (with-syntax* ([type-name(format-id stx "~a*" #'pbuf-type)]
[handler-name (format-id stx "msg-~a" #'type-name)]
[route-name   (symbol->string (syntax->datum
(format-id stx "~a" (syntax->datum #'pbuf-type]
)
   #'[(route-name) #:method "post" (make-route
handler-name type-name)]
;;   #'(quote [(route-name) #:method "post"
(make-route handler-name type-name)])
   

;;(routing announce-file)  ; If I use this (i.e. outside the
dispatch-rules) in combination with the 'quote' version above, I see
the correct thing

(define-values (dispatch-request url-for)
  (dispatch-rules
   (routing announce-file)
   [("create-user") #:method post process-create-user]
   ...more routes here...
)

Error is:

racket network/routing.rkt
~/app/network/routing.rkt:194.2: dispatch-rules: bad syntax
  in: (dispatch-rules (routing announce-file) (("create-user")
#:method post process-create-user) ...
  context...:
   
/Applications/Racket_v6.6/collects/syntax/parse/private/runtime-report.rkt:698:0:
error/report
   
/Applications/Racket_v6.6/collects/syntax/parse/private/runtime-report.rkt:28:0:
call-current-failure-handler
   standard-module-name-resolver


As mentioned in the comments, it does generate (the quoted form of)
the correct thing if I:

1) inside the macro, comment in the 'quote' line and comment out the
line above it
2) comment OUT the '(routing announce-file) that is inside dispatch-rules
3) comment IN the (routing announce-user) line that is just above dispatch-rules


My suspicion is that dispatch-rules is a macro and so my macro is not
being expanded inside another macro.  That's not how I thought macros
worked, though, so now I'm really puzzled.

Can anyone clarify this for me?

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