Aha, the xexpr-drop-empty-attributes is probably best, since it will produce consistent forms. Thanks.
BTW what part of the docs are you citing for *(list* Symbol (option AttributeList) XexprList)*? The only definition of X-expressions I'm aware of is here<http://docs.racket-lang.org/xml/index.html?q=x-expression#%28def._%28%28lib._xml%2Fprivate%2Fxexpr-core..rkt%29._xexpr~3f%29%29> . On Mon, Jun 10, 2013 at 11:58 AM, Jay McCarthy <jay.mccar...@gmail.com>wrote: > The type of Xexpr is... > | AtomicContent > | (list* Symbol (option AttributeList) XexprList) > > It sounds like you have one function F that you would like to give the > type "Xexpr -> Value", but you are having a problem when you apply it > to the AttributeList. You should have such a problem, because an > AttributeList is not an Xexpr, so your types are wrong. > > In other words, if you want to recursively process an Xexpr, then you > need two functions, one for attribute lists and one for xexpr lists. > > Finally, I find it convenient when automatically processing Xexprs to > ensure that xexpr-drop-empty-attributes is #f so that there is always > an attribute list and do: > > (match xe > [(list* tag attrs content) ....]) > > > > On Mon, Jun 10, 2013 at 12:40 PM, Matthew Butterick > <mb.list.a...@gmail.com> wrote: > > Consider an x-expression that represents an XML tag, so it has the > general > > form > > > > '(tag ((attr-name "attr-value") ... ) content ...) > > > > The attributes or content might be omitted, of course. > > > > When I recursively process these expressions, I start by decomposing the > > x-expression into components: > > > > tag > > ((attr-name "attr-value") ... ) > > (content ...) > > > > The problem that surfaces in a recursive-processing context is that the > list > > of content might have the same form as an attribute expression, e.g., > > > > ((field-1 "value-1") (field-2 "value-2")) > > ((p "some text") (p "some more text")) > > > > Is there a test I could use to reliably disambiguate between these two > > cases, short of creating a new struct for x-expressions? Seems like I'm > > overlooking some middle ground. > > > > > > > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > > > > > > -- > Jay McCarthy <j...@cs.byu.edu> > Assistant Professor / Brigham Young University > http://faculty.cs.byu.edu/~jay > > "The glory of God is Intelligence" - D&C 93 >
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