Thanks David. Spot on.

a

From: Beginners [mailto:beginners-bounces@haskell.org] On Behalf Of David McBride
Sent: 12 August 2013 21:52
To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell
Subject: Re: [Haskell-beginners] Text.XML.writeFile question

When you use overloadedstrings, it will type all literal strings as IsString a => a as a type.  Unfortunately your tsString is not a literal, it is a run time function that always returns a string and a string is not a filepath.

You should be able to do fmap fromString tsString, provided you import Data.String.

On Mon, Aug 12, 2013 at 4:35 PM, Alan Buxton <alanbuxton@gmail.com> wrote:

Hi

I am trying to write an XML file where the filename is created based on a timestamp. Simplified version below. This won’t compile – I get this error in doWrite2

filepathtest.hs|24 col 17 error| Couldn't match expected type `system-filepath-0.4.7:Filesystem.Path.Internal.FilePath'                                                  

||             with actual type `String'

|| In the second argument of `writeFile', namely `t1'

|| In a stmt of a 'do' block: writeFile def t1 doc

|| In the expression:

||   do { t1 <- tsString;

||        writeFile def t1 doc }

Somehow the String “text.xml” in doWrite1 is converted into a FilePath, but not the String t1 in doWrite2. What am I doing wrong?

  {-# LANGUAGE OverloadedStrings #-}

  module Filepathtest  where

  import Text.XML

  import Data.Time.Clock.POSIX (utcTimeToPOSIXSeconds)

  import Data.Time.Clock  (getCurrentTime)

  import Prelude hiding (writeFile, FilePath)

  tsString :: IO String

  tsString = do

    x <- getCurrentTime

    let x' = show $ floor $ utcTimeToPOSIXSeconds x

    return x'

  doWrite1 :: Document -> IO ()

  doWrite1 doc =

    writeFile def "test1.xml" doc

  doWrite2 :: Document -> IO ()

  doWrite2 doc = do

    t1 <- tsString

    writeFile def t1 doc

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