Re: makeRelative

Herbert Valerio Riedel writes:

Jon Fairbairn writes:

...

So I want

makeRelative "/var/www/this_server/foo/bar/" "/var/www/this_server/bob"

to return "../../bob"

[...]

...

Is there any reason that System.FilePath.Posix.makeRelative should not do this? I don’t know enough about non-posix filesystems to know whether it even makes sense elsewhere.

I don't know whether this might the reason (or whether it is relevant at all for the API at hand) but you can't implement this function properly w/o turning it into an IO action

Ah, well spotted. In my use case I happen to know the structure of the directories, so hadn’t considered that symlinks can make it impossible to do purely. Given that in System.Directory there is makeRelativeToCurrentDirectory:: FilePath -> IO FilePath, we should probably have a function in there makeRelativeToPath:: FilePath -> FilePath -> IO FilePath. and do it properly. Whether this should be makeRelativeToPath:: FilePath -> FilePath -> IO (Maybe FilePath) (cf Ian Lynagh’s post) is another argument. I don’t like relying on exceptions in general, but once we’re in the IO monad (where exceptions seem to be used willy-nilly), throwing something when no relative path is possible seems not entirely unreasonable. -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk