> Nota Poin wrote on 02/11/2016 04:48 AM:
>> But there's no way I've ever been able to figure to produce generated text
>> that is just a flat list of strings, if I ever want to have conditional
>> decisions about what to go in that list.
I'm supposing you know that Racket has at least two native representations
(X-expression and SXML) for HTML-like structures, so hacking HTML tags by hand
is unnecessary.
But if you must, there's a #lang for that:
Here's the literal translation of your code in `scribble/text`, which
automatically splices all `list`s it finds:
#lang scribble/text
@(define prev "foo")
@(define next "bar")
@(if prev
@(if next
@list{<p id="navigation">
<a href="@|prev|">Prev</a>
<a href="@|next|">next</a>
</p>}
@list{<p id="navigation">
<a href="@|prev|">Prev</a>
</p>})
@(if next
@list{<p id="navigation">
<a href="@|next|">next</a>
</p>}
@list{<p id="navigation">
</p>}))
A more compact refactoring of same:
#lang scribble/text
@(define prev "foo")
@(define next "bar")
<p id="navigation">
@(if prev @list{<a href="@|prev|">Prev</a>} "")
@(if next @list{<a href="@|next|">next</a>} "")
</p>
And here's the refactored version in `pollen/pre`, which is based on
`scribble/text`. It does not splice `list`s by default, but it has a splicing
operator `@`, and also a `when/splice` that lets you do single-branch
conditionals.
#lang pollen/pre
◊(define prev "foo")
◊(define next "bar")
<p id="navigation">
◊when/splice[prev]{<a href="◊|prev|">Prev</a>}
◊when/splice[next]{<a href="◊|next|">next</a>}
</p>
Here's an HTML-free variant in `pollen/markup` that produces an equivalent
X-expression (which can be easily converted to HTML):
#lang pollen/markup
◊(define prev "foo")
◊(define next "bar")
◊p[#:id "navigation"]{
◊when/splice[prev]{◊a[#:href ◊prev]{Prev}}
◊when/splice[next]{◊a[#:href ◊next]{next}}}
Finally, we can throw in a macro for fun:
#lang pollen/markup
◊(define prev "foo")
◊(define next "bar")
◊(define-syntax-rule (cond-nav id text ...)
◊when/splice[id]{◊a[#:href ◊id text ...]})
◊p[#:id "navigation"]{
◊cond-nav[prev]{Prev}
◊cond-nav[next]{next}}
Enjoy.
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