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I use a couple of macros to define tag functions that automatically branch into other functions
depending on the current output target format. This allows me to put the format-specific tag
functions in separate files that have separate places in the dependency chain. So if only the HTML
tag functions have changed and not those for PDF, the makefile can ensure only the HTML files are
rebuilt.
@defproc[#:kind "syntax"
(poly-branch-tag (tag symbol?))
(poly-branch-tag (tag-id symbol?))
(-> txexpr?)]
Defines a new function @racket[_tag] which will automatically pass all of its arguments to a
Defines a new function @racket[_tag-id] which will automatically pass all of its arguments to a
function whose name is the value returned by @racket[current-poly-target], followed by a hyphen,
followed by @racket[_tag]. So whenever the current output format is @racket['html], the function
defined by @racket[(poly-branch-tag _p)] will branch to a function named @racket[html-p]; when the
current format is @racket['pdf], it will branch to @racket[pdf-p], and so forth.
You @emph{must} define these branch functions separately, and you must define one for @emph{every}
output format included in the definition of @racket[poly-targets] in this file’s @racket[setup]
submodule. If you do not, you will get “unbound identifier” errors at expansion time.
The convention in this project is to define and provide these branch functions in separate files:
see, e.g., @filepath{tags-html.rkt}.
Functions defined with this macro @emph{do not} accept keyword arguments. If you need keyword
arguments, see @racket[poly-branch-kwargs-tag].
@margin-note{The thought behind having two macros so similar is that, by cutting out handling for keyword
arguments, @racket[poly-branch-tag] could produce simpler and faster code. I have not verified if
this intuition is meaningful or correct.}
@defproc[#:kind "syntax"
(poly-branch-kwargs-tag (id symbol?))
(poly-branch-kwargs-tag (tag-id symbol?))
(-> txexpr?)]
Works just like @racket[poly-branch-tag], but uses Pollen’s @racket[define-tag-function] so that
keyword arguments will automatically be parsed as X-expression attributes.
Additionally, the branch functions called from the new function must accept exactly two arguments:
a list of attributes and a list of elements.
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