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#lang scribble/manual
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@(require scribble/eval pollen/cache pollen/setup (for-label racket (except-in pollen #%module-begin) txexpr pollen/tag pollen/render xml pollen/pagetree))
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@(define my-eval (make-base-eval))
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@(my-eval `(require pollen pollen/template xml))
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@title{Tag}
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@defmodule[pollen/tag]
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Convenience functions for working with tags.
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@defproc[
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(default-tag-function
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[id txexpr-tag?]
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[kw-attr-name keyword?]
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[kw-attr-value string?] ... ...)
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(-> txexpr?)]
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Make a default tag function for @racket[_id]. The new tag function takes an optional set of X-expression attributes (@racket[txexpr-attrs?]) followed by X-expression elements (@racket[txexpr-elements?]). From these, the tag function creates a tagged X-expression using @racket[_id] as the tag.
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@examples[
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(require pollen/tag)
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(define beaucoup (default-tag-function 'em))
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(beaucoup "Bonjour")
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(beaucoup '((id "greeting")) "Bonjour")
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]
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Entering attributes this way can be cumbersome. So for convenience, the new tag function provides an alternative: any keyword arguments and their values will be interpreted as attributes.
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@examples[
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(require pollen/tag)
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(define beaucoup (default-tag-function 'em))
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(beaucoup #:id "greeting" #:class "large" "Bonjour")
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]
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You can also provide keyword arguments to @racket[default-tag-function] itself, and they will become default attributes for every use of the tag function.
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@examples[
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(require pollen/tag)
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(define beaucoup-small (default-tag-function 'em #:class "small"))
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(beaucoup-small #:id "greeting" "Bonjour")
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]
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Pollen also uses this function to provide the default behavior for undefined tags. See @racket[#%top].
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Note that while default tag functions are typically used to generate tagged X-expressions, they don't enforce any restrictions on input, so they also do not guarantee that you will in fact get a valid tagged X-expression as output. This is intentional — default tag functions are a coding convenience, and their output is likely to be processed by other tag functions, so raising the error here would be premature.
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@examples[
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(require pollen/tag)
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(define strange (default-tag-function 'div #:class "bizarre"))
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(code:comment @#,t{Invalid data types for elements})
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(strange + *)
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(code:comment @#,t{Double "class" attribute})
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(strange #:class "spooky")
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]
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@defform[
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(define-tag-function
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(tag-id attr-id elem-id) body ...)]
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Helper function for making custom tag functions. Handles parsing chores, including conversion of keyword arguments into attributes (described in @racket[default-tag-function]), and parses other attributes and elements normally.
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@examples[
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(require pollen/tag)
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(define-tag-function (tag-name attrs elems)
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`(new-name ,(cons '(zim "zam") attrs) ,@elems))
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(tag-name "Hello world")
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(tag-name '((key "value")) "Hello world")
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(tag-name #:key "value" "Hello world")
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] |