From: Lucian Mogosanu <lucian.mogosanu@gmail.com>
Date: Tue, 26 Feb 2019 21:13:17 +0000 (+0200)
Subject: drafts: 087
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drafts: 087
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+---
+postid: 087
+title: A feed parser for Common Lisp programs
+date: February 18, 2019
+author: Lucian Mogoșanu
+tags: tech, tmsr
+---
+
+This is the second part of [a series][tmsr-schedule-i] on building
+blocks for [Feedbot][feedbot].
+
+Now that we have an [XML parser][s-xml] on hand, we can use that to
+obtain [RSS][rss] and [Atom][rss] feeds in a structured format. Once
+again, as far as heathendom goes we are lucky -- one Kyle Isom has
+provided us with a feed parser, cl-feedparse, that is under three
+hundred lines of neat Lisp code, and quite importantly, it meets the
+spec, as can be seen below.
+
+The code is available as a patch on the [S-XML V tree][s-xml-v].
+
+The remainder of this post a. describes the structure and functionality
+of feedparse; and b. it provides some usage examples.
+
+(cl-)feedparse provides the following simple structure for (RSS/Atom)
+feeds. A feed can be decomposed into its title, kind (RSS or Atom), URL
+and list of feed items. A feed item has the following elements: an ID, a
+title, a (publication) date, a link and a body/description.
+
+In order to obtain a feed, feedparse:
+
+* performs an HTTP request, obtaining the raw feed data;
+* parses the feed, using S-XML's `parse-xml-string`;
+* identifies the kind of feed (`parser-dispatch`); and
+* calls the appropriate parser, `parse-rss` or `parse-atom`.
+
+Both parsers are very easy to understand; the reader is encouraged to
+peruse `feedparse.lisp`.
+
+After we've pressed to `s-xml-feedparse`:
+
+~~~~
+TODO
+~~~~
+
+and imported all the dependencies[^1], we can now run our parser:
+
+~~~~
+TODO
+~~~~
+
+[^1]: Unfortunately, both feedparse depends on Lisp code which is not
+    yet V-ified, namely [Drakma][drakma] and flexi-streams, which on
+    their own depend on other packages. The full set of dependencies is:
+    usocket, chipz, flexi-streams, trivial-gray-streams, chunga,
+    cl-base64, cl-puri and drakma.
+
+    TODO: describe these.
+
+[tmsr-schedule-i]: /posts/y05/082-tmsr-schedule-i.html#selection-63.114-63.159
+[feedbot]: http://btcbase.org/log-search?q=feedbot
+[s-xml]: TODO
+[rss]: https://archive.is/3rHl
+[atom]: https://archive.is/rdl5b
+[s-xml-v]: http://lucian.mogosanu.ro/src/s-xml
+[drakma]: TODO