Hi Alexey Popkov,

Thank you for your comment.

Why do you use the following code snippet in your explanation:

h[path, fileName]

instead of the following form:

{path, fileName}

In fact, the following two commands will give exactly the same results:

NotebookFileName[EvaluationNotebook[]]
NotebookFileName[]

But what I want to tackle here is a general problem, and the command above is only used as an example. More specifically, I want to have a customized function which can combine the outputs of the commands mentioned above to give more elegant and readable results.

Just to illustrate the point of destructuring more clearly: the FullForm of {path, fileName} is List[path, fileName], and h[path, fileName] is just a generalization of this. It empasizes the point that you don't have to use the Head List, you can use any Head.

Things like this are very difficult to understand for me, at least for now. For the sake of clarity, let me express my confusion with the following example:

In[49]:= Clear[a, x, y, b]
{a, List[x, y], b}
{a, {x, y}, b}
{a, Sequence[x, y], b}
{a, h[x, y], b}

Out[50]= {a, {x, y}, b}

Out[51]= {a, {x, y}, b}

Out[52]= {a, x, y, b}

Out[53]= {a, h[x, y], b}

As you can see, after the destructuring, I got three different results.

About the code snippet you are trying to understand. I don't think that Trace can help you in this case. Probably the most difficult part is the pattern _[{path__}, fileName_, __]. This pattern performs a destructuring of the supplied expression based on knowing the exact structure of the latter.

The supplied expression returned by "FileName" /. NotebookInformation[] can look like:

expr = FrontEnd`FileName[{$RootDirectory, "C:", "Users", "APopkov", "Desktop"}, "myNotebook.nb", CharacterEncoding -> "UTF-8"]

Check what the pattern does:

expr /. _[{path__}, fileName_, __] :> h[path, fileName]

h["", "C:", "Users", "APopkov", "Desktop", "myNotebook.nb"]

I hope that starting from this point you can reconst the whole logic yourself.