Question

I have a dynamically constructed file path in haskell that ends up something like this:

/abc/def/../ghi/./jkl

and I’d like to reduce it to the more readable

/abc/ghi/jkl

For printing. Is there a library function to do this in haskell? I’ve looked all over and can’t find one. It’s not too hard to write, but it’s a bit messy because you have to “look ahead” for “..”s, and I’d rather use a baked-in function if I can.

Answer 1

Beware that this is not simply a string processing question when links are involved:

$ mkdir -p foo/bar
$ ln -s foo/bar baz
$ echo gotcha! >foo/quux
$ cat quux
cat: quux: No such file or directory
$ cat baz/../quux
gotcha!

So you need to do IO.

The nearest I can find to what you want is canonicalizePath from System.Directory. It returns a path starting from the root directory, so you may want to use it in conjunction with makeRelative, also from System.Directory. But it does run in IO.