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."

On Mon, Jun 20, 2011 at 7:30 PM, Alejandro Serrano Mena wrote:

Maybe you can directly distinguish if the parser returned an error (Left) or not (Right), instead of using lefts and rights:

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

main = do [inpFileName] <- getArgs putStrLn ("Parsing "++inpFileName++"...") result <- parseCSVFromFile inpFileName case result of Left error -> do print "Parse error: " print error Right csv -> print csvL putStrLn "All done."

Yes, you right, this is better, then printing empty error list.

2011/6/17 Dmitri O.Kondratiev

...

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."

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