[Haskell-beginners] PHP vs Haskell... a challenge!

Sean Charles sean at objitsu.com
Thu Mar 17 01:00:13 CET 2011

I tried in vain using Text.CSV to write a small utility for myself that 
would *simply* map a CSV file across a template, specifically for 
mass-producing Drupal nodes from a CSV file... Here's what the Haskell 
code has to compete with :-

harry,15,"Web nerd"

UPDATE foo SET rating = @1, role = '@2' where name = '@0';

And the PHP code that is used to produce ANY output from the template 
and CSV data (forget injection attacks and all that for now, this is 
proof-of-concept remember)...

$template = file_get_contents($argv[1]);
if ($fh=fopen($argv[2],"r")) {
   while($line = fgetcsv($fh)) {
     foreach ($line as $k => $v ) $line['@'.$k] = $v;
     echo strtr($template,$line)."\n";

Note that I have had to remap the index keys to @n in order not to 
accidentally hit any numerical data that may be in the template. This is 
my test, the *real* template creates a Drupal node dynamically and has 
lots of [0]['value'] bits in it so I had to do this, I will allow any 
shortcuts to be used though as I would have liked to have coded the 
utility in Haskell to get better at it but tonight it defeats me!

Here then is my unsatisfactory code and no, it doesn't compile or work 
very well as I am still trying hard with it!
I want to learn!

Still my biggest headache is type matching and deciphering the sometimes 
complete gibberish output from the type inference system when I screw 
up... I am finding it very hard to work out what I did wrong at times. 
Sitting here with Real World Haskell is proving fruitless tonight. :(

Here's the rubbish code...

import Text.CSV
import System.Environment
import System.IO
import Text.ParserCombinators.Parsec.Error

main = do
   args <- getArgs
   case length args of
     2 -> do
       csvdata <- parseCSVFromFile (last args)
     (\error -> print error)
     (\csvdata -> processData (head args) csvdata)
     _ -> print "Usage: csvsql template datafile.csv (options later!)"

     csvdata is [CSV]
     a CSV is [Record]
     a Record is [Field]
     a Field is String
processData :: String -> CSV -> IO ()
processData filename csvdata = do
   tin <- openFile filename ReadMode
   template <- hGetContents tin
   processRow template csvdata
   hClose tin
   return ()

processRow :: String -> [Record] -> String
processRow template row = "eric" ++ template

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