Re: [Haskell-cafe] Text.CSV questions

17 Jun 2011


      On Fri, Jun 17, 2011 at 1:04 PM, Vincent Hanquez  wrote:
...
On 06/17/2011 10:00 AM, Dmitri O.Kondratiev wrote:
...
Hi,
I try to parse csv file with Text.CSV, like this:
import Text.CSV
import System
main = do
    [inpFileName] <- getArgs
    putStrLn ("Parsing "++inpFileName++"...")
    let result = parseCSVFromFile inpFileName
    print result
=== As a result I get:
No instance for (Show
                   (IO (Either Text.Parsec.Error.ParseError CSV)))
  arising from a use of `print'
 Possible fix:
  add an instance declaration for
  (Show (IO (Either Text.Parsec.Error.ParseError CSV)))
=== Question:
How to add a Show instance for "(IO (Either Text.Parsec.Error.ParseError
CSV)))" ?
Hi Dmitri,
you don't add a show instance for IO, but you "unwrap" the IO Monad first
and then show the result.
let result = parseCSVFromFile inpFileName
should be:
result <- parseCSVFromFile inpFileName
--
Vincent
Thanks everybody!  This is how I solved it:

import Text.CSV
import Data.Either
import System
import Data.List

main = do
     [inpFileName] <- getArgs
     putStrLn ("Parsing "++inpFileName++"...")
     result <- parseCSVFromFile inpFileName
     let errors = lefts [result]
     let csvL = rights [result]
     print "CSV list"
     print csvL
     print "Errors"
     print errors
     putStrLn "All done."