From 5b063193f389ef472366e4355a683f1843f29733 Mon Sep 17 00:00:00 2001 From: Gregor Kleen Date: Fri, 27 May 2016 19:40:18 +0200 Subject: structure --- provider/posts/blog-rss.md | 43 ------------------------------------------- 1 file changed, 43 deletions(-) delete mode 100644 provider/posts/blog-rss.md (limited to 'provider/posts/blog-rss.md') diff --git a/provider/posts/blog-rss.md b/provider/posts/blog-rss.md deleted file mode 100644 index 095ff56..0000000 --- a/provider/posts/blog-rss.md +++ /dev/null @@ -1,43 +0,0 @@ ---- -title: dirty-haskell.org´s rss feeds -published: 2015-03-29 -tags: Blog Software ---- - -I extended the software suite inherited from [math.kleen.org](http://math.kleen.org) to include support for rss feeds. -The heart of the issue is a ~80 line haskell script I chose to call, in a bout of creativity, "generate-rss.hs". -The script uses the [feed](http://hackage.haskell.org/package/feed-0.3.9.2) package. - -generate-rss.hs gets passed a title and a list of paths below ./lists to incorporate as items. -It generates an empty feed structure, adds title and a (hardcoded) base url for RSS metadata, and iterates over the given paths — generating for each path an item to be included in the finished feed. -This procedure makes use of a state monad (StateT (Feed, Maybe ClockTime) IO ()) to sequentially add items to the feed and keep track of the modification/change time of the newest path examined. -Each item carries a title, an url, a date, and contents as follows: - -- The date used is the modification/change time of the path supplied as a command line argument at the beginning of the program (usually a symbolic link in ./lists) — as such it is the time the post was linked into the particular list we´re generating a RSS feed for (this was not a deliberate design choice but a side effect of the canonical implementation — it was later decided that this behaviour was in fact the one expected all along). -- The url is generated by following, recursively, the trail of symbolic links starting in ./lists, assuming the final target is indeed in ./posts, and forming the filename of that target into a (hopefully) functional url in a hardcoded fashion. -- The title is extracted from the markdown file using a function shamelessly copied from extract-title.hs (The author wrote that one too, after all). -- The contents are read into Pandoc and rendered into [AsciiDoc](http://en.wikipedia.org/wiki/AsciiDoc) format (it seemed convenient at the time). - -Along the way two helper functions were introduced — if an implementation of those already exists in Prelude or somewhere else common please mail in a comment: - -~~~ {.haskell} -(<->) :: [(a -> b)] -> a -> [b] -[] <-> _ = [] -(f:fs) <-> x = (f x:fs <-> x) - -(<-->) :: [(a -> a)] -> a -> a -[] <--> x = x -(f:fs) <--> x = fs <--> (f x) -~~~ - -## Update ## - -~~~ {.haskell} -import Control.Applicative ((<*>), pure) - -(<->) fs = (<*>) fs . pure - -(<-->) = flip $ foldl (.) id -~~~ - -Thanks, viktor. -- cgit v1.2.3