Macro containing a list of elements that each have optional keyword options

[Brian Adkins]

I'm working on a macro to allow the following:

(routes

 ("/foo" foo-handler #:method put)

 ("/bar" bar-handler #:methods (put update))

 ("/baz" baz-handler))

The idea is that you could restrict a route based on the HTTP method either for one method using #:method or for a list of methods using #:methods. I tried using some ideas from the following examples:

https://docs.racket-lang.org/syntax/Optional_Keyword_Arguments.html

https://docs.racket-lang.org/syntax/More_Keyword_Arguments.html

The attempt below does not work, and from my debugging I think it's probably the wrong approach. If there are examples of this sort of thing, I'd love to see them.

Thanks,

Brian Adkins

(define-syntax (routes stx)

  (syntax-parse stx

    [ (routes (route:string

               handler:id

               (~alt (~optional (~or* (~seq #:methods (methods:expr ...))

                                      (~seq #:method method:expr))

                                #:name "#:method, or #:methods option")

                     (~optional (~seq #:when guard:expr)

                                #:name "#:when option"))

               ...)

              ...)

      (with-syntax ([ name  (format-id stx "axio-routes") ])

        #'(define name (list (list route handler 'method (list 'methods ...)) ...)))]))

[Brian Adkins]

The following got me over the main hurdle:

(define-syntax (routes stx)

  (syntax-parse stx

    [ (routes (element ...) ...)

      (with-syntax ([ name  (format-id stx "axio-routes") ])

        #'(define name (list (route-element element ...) ...)))]))

(define-syntax (route-element stx)

  (syntax-parse stx

    [ (route-element route:string

                     handler:id

                     (~alt (~optional (~or* (~seq #:methods (methods:expr ...))

                                            (~seq #:method method:expr))

                                      #:name "#:method, or #:methods option")

                           (~optional (~seq #:when guard:expr)

                                      #:name "#:when option"))

                     ...)

      (with-syntax ([ m  (or (attribute method)  #'#f) ]

                    [ ms (or (attribute methods) #'#f) ])

        #'(list route handler 'm 'ms))]))

(routes

 ("/foo" foo-handler #:method put)

 ("/bar" bar-handler #:methods (put update))

 ("/baz" baz-handler))

axio-routes

==> '(("/foo" #<procedure:foo-handler> put #f) ("/bar" #<procedure:bar-handler> #f (put update)) ("/baz" #<procedure:baz-handler> #f #f))

Now I just need to normalize to a list of HTTP methods vs. having separate fields. 

[Brian Adkins]

(define-syntax (routes stx)

  (syntax-parse stx

    [ (routes (element ...) ...)

      (with-syntax ([ name  (format-id stx "axio-routes") ])

        #'(define name (list (route-element element ...) ...)))]))

(define-syntax (route-element stx)

  (syntax-parse stx

    [ (route-element route:string

                     handler:id

                     (~alt (~optional (~or* (~seq #:methods (methods:expr ...))

                                            (~seq #:method method:expr))

                                      #:name "#:method, or #:methods option")

                           (~optional (~seq #:when guard:expr)

                                      #:name "#:when option"))

                     ...)

      (with-syntax ([ method-list (let ([ m  (attribute method)  ]

                                        [ ms (attribute methods) ])

                                    (cond [ m    (list m) ]

                                          [ ms   ms       ]

                                          [ else '()      ]))]

                    [ guard-func (let ([ fun (attribute guard) ])

                                   (if fun

                                       fun

                                       #f)) ])

        #'(list route handler 'method-list guard-func))]))

(routes

 ("/foo" foo-handler #:method put)

 ("/bar" bar-handler #:methods (put update) #:when use-bar-handler?)

 ("/baz" baz-handler))

axio-routes

==>  '(("/foo" #<procedure:foo-handler> (put) #f) ("/bar" #<procedure:bar-handler> (put update) #<procedure:use-bar-handler?>) ("/baz" #<procedure:baz-handler> () #f))

I know it ain't pretty yet, but it works now, so I can enhance it later. I should probably use a struct for each route vs. a list.

[Sorawee Porncharoenwase]

You could use (splicing) syntax class to help with normalization:

#lang racket

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

(begin-for-syntax
  (define-splicing-syntax-class methods-cls
    #:attributes (methods)
    (pattern (~seq #:methods (method:expr ...))
             #:with methods #'(list 'method ...))
    (pattern (~seq #:method method:expr)
             #:with methods #'(list 'method)))

  (define-syntax-class route-cls
    (pattern (route:string
              handler:id
              (~alt (~optional ms:methods-cls
                               #:name "#:method, or #:methods option")
                    (~optional (~seq #:when guard-e:expr)
                               #:name "#:when option")) ...)
             #:with methods #`#,(or (attribute ms.methods) #'(list))
             #:with guard #`#,(attribute guard-e))))

(define-simple-macro (routes :route-cls ...)
  #:with name (format-id this-syntax "axio-routes")
  (define name (list (list route handler methods guard) ...)))

(define (foo-handler) 0)
(define (bar-handler) 0)
(define (baz-handler) 0)
(define (use-bar-handler?) 0)

(routes
 ("/foo" foo-handler #:method put)
 ("/bar" bar-handler #:methods (put update) #:when use-bar-handler?)
 ("/baz" baz-handler))

axio-routes

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[Brian Adkins]

Thanks your idea cleans it up nicely!  I've broken up the code into 4 file and placed them in a gist:

https://gist.github.com/lojic/842619ab2c59a2c96960f9ccd30bc136

I'm not thrilled with the fact that the routes macro has to export the axio-routes binding. I expect there is a better way to communicate between the routes macro and find-route function.

I'll add interpolation to the URL paths next e.g.  (route "/user/~id" ...)