World: r4wp

Anton, but then you could never get an empty target, and you would 
have to compare to %./ as your empty value.

And then make sure that wasn't the end of the original path.

Andreas, can you give examples, to make sure I'm clear?

Would behave mostly as the current split-path does.

(For the common cases.)

So this is OK for you: %/c/test/test2/ [%/c/test/ %test2/]

Yes, that's what I'd expect.

I'd also prefer a stronger invariant, as REJOIN is relatively weak 
for joining path components.

Something more along the lines of

set [d b] split-path f
f = d/:b

what do you mean with an empty target?  %./ just means the target 
is a directory, the actual directory

OK, using that as a quality test, here's where the current SPLIT-PATH 
fails:
Path quality failed: %/ %/none
Path quality failed: %// %/
Path quality failed: %. %./none
Path quality failed: %./ %./none
Path quality failed: %./. %././
Path quality failed: %.. %../none
Path quality failed: %../ %../none
Path quality failed: %../.. %../../
Path quality failed: %foo/.. %foo/../
Path quality failed: %foo/. %foo/./
Path quality failed: %foo/../. %foo/.././
Path quality failed: http:// http:/
Path quality failed: http://..http://../
Path quality failed: http://.http://./
Path quality failed: http://../.http://.././

And here's where my proposed SPLIT-PATH fails:
Path quality failed: %. %/.
Path quality failed: %.. %/..

%. is tricky :)

Anton, which is the behavior question. Do you expect SPLIT-PATH to 
return a target you can write to (i.e. a file)?

Here's a few example values and what I would expect: 

http://sprunge.us/AaDJ


Where there is a third column, current R3 split-path differs from 
what I'd expect, and the third column is what split-path returns 
currently.

Great! Since I haven't had coffee yet, the second column is *always* 
what you expect, correct?

Yes.

Got it.

But with a "path component"-based invariant, the %. %.. and %/ cases 
will require more work to reconcile.


With a "string"-based invariant (rejoin), those cases could more 
easily be described with the neutral %"" element:

Here's some examples based on a string-based invariant:
http://sprunge.us/VeeH


Which is, I guess, what your proposed split-path already implements 
:)

Yes, I believe that matches my current proposal.

Basically strips off everything past the last / as target.

And where it fails the path (p/:t) invariant is in these cases:
Path quality failed: %"" %/
Path quality failed: %foo %/foo
Path quality failed: %. %/.
Path quality failed: %.. %/..

A slightly better path-based invariant:

set [d b] split-path f
clean-path/only f = clean-path/only d/:b

It doesn't match your expected results in a number of cases though.

I don't have a *nix VM up here to check basename and dirname results.

That might be something else to consider.

Using the clean-path test, here's where my proposed version fails:

Path quality failed: %"" %/
         %""     ; clean-path test
         %/      ; clean-path p/:t
Path quality failed: %foo %/foo
         %foo    ; clean-path test
         %/foo   ; clean-path p/:t

My first examples should match dirname/basename exactly.

OK, great.

In effect, that is :)

dirname/basename does a clean-path before splitting.

:-) Let me play with an idea here for a bit.

Let's widen the discussion a bit. Spitting a string at a delimiter. 
Easy enough to define clear behavior if the series contains the delimiter, 
but what if it doesn't? Most split funcs return an array, splitting 
at each dlm. If no dlm, return the original series as the only element 
in that array. 


What if we always want to return two elements? e.g., we have a SPLIT-AT 
func that can split a series into two parts, given either an integer 
index or value to match. Let's also give it a /LAST refinement, so 
it can split at the last matching value found, like FIND/LAST works. 


Given that, what do you expect in the case where the dlm (e.g. "=") 
is not in the series?

    SPLIT-AT "abcdef" "="   == [? ?]
    SPLIT-AT/LAST "abcdef" "="    == [? ?]

I haven't had the time to follow all the discussion in detail, but 
to me, the second part of split-path should NEVER return a directory 
path. 


when doing   set [dir file]  I should be able to count on the fact 
that the second part is either a file or none.  The same for the 
first part which should always be none or a dir.  I have my own implementation 
in R2 which makes this strict and it simplifies a lot of code.
so we can do with absolute certainty:

if second set [dir file] split  path [   ]


IIRC some of the versions of my split perform a clean-path to simplify 
and add robustness to the result.

Thanks for posting Max. With 5 of us talking about it, we have 5 
opinions so far. :-) The one thiing we all seem to agree on is that 
we want consistent behavior, which we don't have right now.

Maxims method sounds reasonable

Re: 

One test missing in your collection:
%foo [%./ %foo]

- this test violates the "invariant"

Re:

%/c/test/test2/ [%/c/test/ %test2/]


- this test does not violate anything but it does not split the "pathfile" 
to "path" and "file" parts

hmm, I may be wrong in "it does not violate anything" - in fact, 
it contradicts the help string of the function

(I do not object against adjustment, but would expect the help string 
to be changed as well to be compatible with this)

(if it is the preferred behaviour)

Regarding the split-path behaviour in the %foo case. I stongly object 
against the proposal to obtain [%. %foo], since for example INCLUDE 
whan obtaining %foo with empty path uses INCLUDE-CTX/PATH to find 
%foo (which may even exclude the %./ directory if it is not in INCLUDE-CTX/PATH), 
while when obtaining %./foo it just finds the file in the current 
directory (which is not equivalent)

IMHO %foo should return  [none %foo]

split-path shoudn't invent information which isn't given to it

As said, I prefer [%"" %foo] to have the invariant that file = rejoin 
split-path file

question is, is that invariant useful? 


really, I like consistency almost above all else, but I prefer when 
it not just neutral.   getting empty file specs is very awkward to 
use and doesn't work well with all the none transparency which makes 
a lot of the conditional code so easy to read.  one reason this is 
so readable in REBOL is the limited use of equality operations, when 
doing complex decision making.

question is, is that invariant useful?
 - for me it is, but, of course, it is a matter of preference

I agree.

I prefer

split-path %foo
== [%./ %foo]


The reason is because I believe split-path shouldn't require an extra 
check if all you want to do is read the base directory that a file 
is in.  I think this is a common use of split-path.