makeRelative

[wren ng thornton]

On 9/30/12 10:24 AM, Ben Millwood wrote:
> 2. surely this issue can be avoided by using something like
> System.Directory.canoncalizePath before calling makeRelative. I think
> doing things that way would separate the pure and IO parts of the
> algorithm much better, and allow users to ignore the possibility of
> symlinks when that was appropriate for their use.

Indeed. While it's important to be able to capture correct POSIX 
behavior, there's also plenty of room for legitimate uses of naive 
relative paths. In particular, the former is more important when 
accessing the filesystem, whereas the latter is more important when 
generating files[1].

So long as the documentation includes das blinkenlights, to ensure that 
users know which behavior they're getting, I think it's fine to offer 
the naive implementation. If folks consider it "unsafe" enough to 
warrant name changes, we could always:

     canoncalizePath :: Path -> IO Path

     naiveMakeRelative :: Path -> Path -> Path

     makeRelative x y = do
         x <- canoncalizePath x
         y <- canoncalizePath y
         return $! naiveMakeRelative x y


[1] Because you know the filesystem structure you'll be generating, so 
you know whether this will be an issue. And because the files you'll be 
generating don't yet exist and so can't be cannonicalized, as others 
have mentioned.

-- 
Live well,
~wren