Contents: Chronological Listing Of Exercises
July 2, 2010
You may have noticed that the Contents page changed recently. Previously the Contents page listed all the exercises in chronological order. Now, there are four listings of the exercises, in chronological order, reverse chronological order, permuted by the words in the title and summary, and organized manually by themes.
The four listings all derive from a single source. The file praxis.info consists of records separated by blank lines, fields on a single line with field name followed by a tab character followed by the data element. Here is an excerpt, which shows the header at the beginning of the file followed by the first two records:
praxis.info
number exercise number
file base name of files
pubmon month of publication
pubday day of publication
pubyear year of publication
title formatted title
ptitle plain title
blurb formatted blurb
pblurb plain blurb
exer exercise sub-page number
soln solution sub-page number
extra extra info sub-page number
codepad eight-character codepad index
theme category in which exercise appears
name/value pairs on a line separated by tabs,
with records separated by blank lines
the "number" field must appear first, others
may be in any order, and are optional
----+----1----+----2----+----3----+----4----+----5----+----6
number 1
file rpn-calculator
pubmon 2
pubday 19
pubyear 2009
title RPN Calculator
blurb Evaluate numeric expressions at the command line
exer 1
soln 2
codepad fjzlC50x
theme Parsing
number 2
file sieve-of-eratosthenes
pubmon 2
pubday 19
pubyear 2009
title Sieve of Eratosthenes
blurb A Scheme implementation of an ancient algorithm
exer 1
soln 2
codepad wI14BJ8Q
theme Prime Numbers
Four programs manipulate the data from the praxis.info file to produce the four listings. The output has elements of html, but WordPress adds the surrounding context; here is the corresponding excerpt from the listing in chronological order:
<table cellpadding="10">
<tr><td>1</td><td>19 Feb 2009</td><td><a href="/2009/02/19/rpn-calculator/">RPN Calculator</a>: Evaluate numeric expressions at the command line</td><td><a href="/2009/02/19/rpn-calculator/">exercise</a> <a href="/2009/02/19/rpn-calculator/2/">solution</a> <a href="http://programmingpraxis.codepad.org/fjzlC50x">codepad</a></td></tr>
<tr><td>2</td><td>19 Feb 2009</td><td><a href="/2009/02/19/sieve-of-eratosthenes/">Sieve of Eratosthenes</a>: A Scheme implementation of an ancient algorithm</td><td><a href="/2009/02/19/sieve-of-eratosthenes/">exercise</a> <a href="/2009/02/19/sieve-of-eratosthenes/2/">solution</a> <a href="http://programmingpraxis.codepad.org/wI14BJ8Q">codepad</a></td></tr>
</table>
Your task is to write programs that read praxis.info and write the two listing files for exercises in chronological order and reverse chronological order. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
Programming Praxis 
[…] Praxis – Chronological Listing Of Exercises By Remco Niemeijer In today’s Programming Praxis exercise our goal is to replicate a script Phil wrote to generate chronological […]
My Haskell solution (see http://bonsaicode.wordpress.com/2010/07/02/programming-praxis-chronological-listing-of-exercises/ for a version with comments):
import Data.List import Data.List.Split import Text.Printf import Text.Regex.Posix toMonth :: Int -> String toMonth m = chunk 3 "JanFebMarAprMayJunJulAugSepOctNovDec" !! (m - 1) item :: [[String]] -> String item xs = printf "<tr><td>%s</td><td>%02s %s %s</td><td>%s: %s</td>\ \<td>%s%s<a href=\"http://programmingpraxis.codepad.org/%s\">\ \codepad</a></td></tr>" (g "number") (g "pubday") (toMonth . read $ g "pubmon") (g "pubyear") (link "" (g "title")) (g "blurb") (link "" "exercise") (link ("/" ++ g "soln") "solution") (g "codepad") where g x = maybe "" last $ find ((== x) . head) xs link :: String -> String -> String link = printf "<a href=\"/%s/%02s/%02s/%s%s/\">%s</a>" (g "pubyear") (g "pubmon") (g "pubday") (g "file") items :: String -> [String] items = map (item . map (splitOn "\t") . lines) . filter (=~ "^number\t[1-9][0-9]*$") . splitOn "\n\n" listing :: ([String] -> [String]) -> String -> String listing f xs = "<table cellpadding=\"10\">" ++ concat (f $ items xs) ++ "</table>" main :: IO () main = do x <- readFile "praxis.info" putStrLn $ listing id x putStrLn $ listing reverse x