[Haskell-cafe] File I/O question

Bjorn Bringert bjorn at bringert.net
Thu Mar 13 05:42:34 EDT 2008

On Wed, Mar 12, 2008 at 10:03 PM, Andrew Coppin
<andrewcoppin at btinternet.com> wrote:
> Don Stewart wrote:
>  > Hey Andrew,
>  >
>  > What are you trying to do? Read and write to the same file (if so, you
>  > need to use strict IO), or are you trying something sneakier?
>  >
>  I have a long-running Haskell program that writes status information to
>  a log file. I'd like to be able to open and read that log file before
>  the program has actually terminated. I have a similar program written in
>  Tcl that allows me to do this, since apparently the Tcl interpretter
>  doesn't lock output files for exclusive access. Haskell, however, does.
>  (This seems to be the stipulated behaviour as per the Report.) If
>  there's an easy way to change this, it would be useful...

How about using appendFile?

"appendFile :: FilePath -> String -> IO ()

The computation appendFile file str function appends the string str,
to the file file."

See http://haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html#v%3AappendFile


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