Re: easily embedding html into Lisp
From: Rob Warnock (rpw3_at_rpw3.org)
Date: 09/15/04
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Date: Wed, 15 Sep 2004 06:19:31 -0500
Andreas Thiele <nospam6329@nospam.com> wrote:
+---------------
| I'd like to introduce a simple approach of embedding html into Lisp.
+---------------
You should look at <http://www.cliki.net/Lisp%20Markup%20Languages>,
which lists several readily-available packages which already do
this (or similar). I tend to use HTOUT, but CL-WHO is also nice.
Also see <http://www.cliki.net/HTML-from-sexpr>.
+---------------
| Let's assume we already have three functions 'table 'tr and 'td.
| Our html code to make a table then might look like
| (table :cellpadding 0 :cellspacing 5
| (tr (td "hello") (td "world")))
| producing
| <table cellpadding="0"
| cellspacing="5"><tr><td>hello</td><td>world</td></tr></table>
+---------------
In HTOUT, that would be written this way.
(with-html-output (s stream)
((:table :cellpadding 0 :cellspacing 5)
(:tr (:td "hello") (:td "world"))))
and generates:
<TABLE CELLPADDING='0' CELLSPACING='5'><TR><TD>hello</TD><TD>world</TD></TR></TABLE>
+---------------
| I assume html tags can be described liked
| <tag-name attribute1=value1 ... > content </tag-name>
+---------------
HTOUT uses keywords for tags, so you don't need to define functions
for all of them. Or, if the first element of a form is itself a list
the CAR of which is a keyword, then the CAAR is taken as the tag and
the CDAR is a property list of "attribute value..." (as shown in the
example above).
+---------------
| Now let's go one step ahead. For each html tag there has to be such a
| function definition.
+---------------
Packages such as HTOUT & CL-WHO don't require this, using symbols in
the keyword package as tag markers instead. Any list whose CAR is not
a keyword or whose CAR is not a list starting with a keyword is taken
to be pure Lisp code, which is simply passed through to the compiler.
Also, inside a WITH-HTML-OUTPUT, macrolets are automatically defined
for several common operations, including going back into HTML mode
from Lisp code [note the use of HTM in the following example].
[There is an alternate syntax available which puts the attributes
in a required list after the tag, but I won't go into that here.]
For example, instead of just saying "hello" and "world", suppose you
wanted to write a function that took an entire list of lists, and gave
you an HTML table row per element, with a data item per sub-element.
Furthermore, suppose you want the first element to be the column-head
labels (that is, use <TH> instead of <TD> on the first row). Here's
one version [the LFD calls produce newlines in the HTML, only needed
for human readability]:
(defun list-html-table (lists &key (stream *standard-output*))
(let ((column-names (car lists))
(rows (cdr lists)))
(with-html-output (s stream)
(:h3 (fmt "Results: ~d rows" (length rows)))
(lfd)
((:table :border 1 :cellspacing 0 :cellpadding 1) ; make compact
(:tr (lfd)
(loop for name in column-names do
(htm ((:th :nowrap) name) (lfd))))
(loop for row in rows do
(htm (:tr (lfd)
(loop for v in row do
(let ((vv (if (or (null v) (string-equal v ""))
" "
(escape-string v))))
(htm ((:td :nowrap) vv) (lfd))))))))
(lfd))))
So this call:
(list-html-table
'(("Name" "Room" "Phone")
("Joe" "37A" "2345")
("Bill" "37B" "5432")
("Sally" "22C" "1234")))
outputs this:
<H3>Results: 3 rows</H3>
<TABLE BORDER='1' CELLSPACING='0' CELLPADDING='1'><TR>
<TH NOWRAP>Name</TH>
<TH NOWRAP>Room</TH>
<TH NOWRAP>Phone</TH>
</TR><TR>
<TD NOWRAP>Joe</TD>
<TD NOWRAP>37A</TD>
<TD NOWRAP>2345</TD>
</TR><TR>
<TD NOWRAP>Bill</TD>
<TD NOWRAP>37B</TD>
<TD NOWRAP>5432</TD>
</TR><TR>
<TD NOWRAP>Sally</TD>
<TD NOWRAP>22C</TD>
<TD NOWRAP>1234</TD>
</TR></TABLE>
+---------------
| When talking about html I must mention Kevin Rosenberg's LML package
| at http://lml.b9.com
+---------------
That one is also listed on the above-mentioned CLiki pages, as well as
his LML2 (for generating XHTML documents).
+---------------
| I am interested in your criticism to my approach.
+---------------
It certainly works. I used something very similar to it [in Scheme]...
before I found HTOUT. ;-}
-Rob
-----
Rob Warnock <rpw3@rpw3.org>
627 26th Avenue <URL:http://rpw3.org/>
San Mateo, CA 94403 (650)572-2607
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