[Haskell-beginners] Text.XML.writeFile question

[David McBride]

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 at 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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