On Mon, Apr 08, 2013 at 04:04:22PM -0700, Erlend Hamberg wrote:

On 8 April 2013 15:45, Hong Yang wrote:

...

I got "not exists ..." from

fileExists <- doesFileExist "~/blah_blah" if fileExists then print "exists ..." else print "not exists ..."

using the directory-1.1.0.2 package, when ~/blah_blah does exist.

When you type “~/blah_blah” in your shell, the *shell* will expand “~” to your home directory, so when you pass “~/foo” to a program, that program never sees “~/foo”, but “/home/user/foo”. In other words, “~/blah_blah” probably does *not* exist.

What you probably should do is to find the user's home directory and prepend that to “blah_blah”. You can find a user's homedir by calling `getHomeDirectory` from `System.Directory`:

Prelude System.Directory> homedir <- getHomeDirectory Prelude System.Directory> putStrLn $ homedir ++ "/blah_blah" /Users/ehamberg/blah_blah

Also, since we are discussing portability, it's a much better idea to do homedir "blah_blah" instead of homedir ++ "/blah_blah", since the former will use the correct path separator character for whatever system it is compiled on. -Brent

There is a package system-filepath http://hackage.haskell.org/package/system-filepath which fixes a lot of quibbles people have with the way filepaths are implemented in haskell. There are apparently a lot of problems with using strings as filepaths, like the fact that they are slow, that they have encoding issues, and that people cannot make a path that is system agnostic. So the operator in that library just joins two filepaths together with the correct slash. On Tue, Apr 9, 2013 at 12:15 PM, Tommy M. McGuire wrote:

On 04/09/2013 07:07 AM, Brent Yorgey wrote:

...

Also, since we are discussing portability, it's a much better idea to do

homedir "blah_blah"

instead of homedir ++ "/blah_blah", since the former will use the correct path separator character for whatever system it is compiled on.

Wait, what? Where'd "" come from?

-- Tommy M. McGuire mcguire@crsr.net

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I didn't even know the standard library had a operator. Here's to learning new things. On Tue, Apr 9, 2013 at 8:06 PM, Brent Yorgey wrote:

...

There is a package system-filepath http://hackage.haskell.org/package/system-filepath which fixes a lot of quibbles people have with the way filepaths are implemented in haskell. There are apparently a lot of problems with using strings as filepaths, like the fact that they are slow, that they have encoding issues, and

On Tue, Apr 09, 2013 at 12:25:10PM -0400, David McBride wrote: that

...

people cannot make a path that is system agnostic.

So the operator in that library just joins two filepaths together with the correct slash.

This is all true, though using system-filepath is still annoying to use because it doesn't play well with everything else in the Haskell ecosystem. However, I was not referring to the () in system-filepath but rather the one in the standard 'filepath' package.

-Brent

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Hi Tommy, On Tue, Apr 09, 2013 at 11:15:01AM -0500, Tommy M. McGuire wrote:

Wait, what? Where'd "" come from?

hoogle or hayoo are great for answering such question, just try searching for . It's from: http://hackage.haskell.org/package/filepath Greetings, Daniel