> I have to understand what (LIST) means in the documentation.

According to the docs cited in

List's terminology and Parentheses in Perl

<updated>

Uppercase "LIST" in perldocs is a argument placeholder for any code ...

• compiled in "list context"
• delivering a "list value" at run time

For instance from the docs for print ...

print LIST; means that ...

• print 1,2,3;

  the two commas are compiled to create a "list value" 1,2,3 for print

• print @a;

  the array @a will be compiled to pass it's content as "list value" ( i.e.not his length from scalar context)

• print func();

  the sub &func will be called in "list context" at run time and return a "list value" from it's last statement. ( compare wantarray )

</updated>

> To understand this:

> > The scalar comma operator returns the last element.

> I must understand in which list it is the last element.

Comma separated lists (sic)

Please compare (updated)

# --- list assignments
@a   = (1,2,3); # list comma
@a   = (1..3);  # list range
($a) = @a;      # deconstruction => $a==1 

# --- scalar assignments
$a = (1,2,3);   # scalar comma
$a = (1..3);    # flip flop operator ... Oo oops!
$a = @a;        # scalar @a == length
[download]

The parens on RHS only do grouping here they do not create a list. Hence the context is propagated to the operators , and ..

@a = and (...)= are "list assignment" imposing "list context".

The range 1..3 returns the list value 1,2,3 in list context only.

You have to think of the whole statement as an op-tree...

• propagating context down
• passing "values" up

With ...

• operators changed by upper context
• operators (sometimes) creating down context

If that's not clear enough please show a short code exemplifying your problem.

HTH

update

you may want to play around yourself with B::Deparse and B::Concise to experiment around with the snippets shown

perl -MO=Deparse,-p -e "CODE"

and

perl -MO=Concise -e "CODE"

(kind of "there is more than one way to word it" ... well )

Even perlglossary which originates from the Camel-Book seems to have been patched afterwards.

For a trained mathematician used to an axiomatic approach it's a painful experience ... >(

So I'd strongly recommend to

• use perlglossary for definitions
• use tests to proof a thesis (runtime)
• use B::Deparse and B::Concise for visualization (compilation)

In an ideal world any other perldoc should be corrected.

I never acquired the Camel book I know it's vast but should be canonic.

It's a long time since I had a look into chromatics "Modern Perl", but it left very consistent impression. So maybe a good source, not sure if he clarifies "lists" there.

update

Modern::Perl#Lists

confusing too.

Thanks LanX for the effort and answers! I am very grateful.

To understand something you need to create a conceptual model of it. I have realized that my model of Perl and the perl interpreter was not adequate.

By following your advice to deparse the generated code, I have start to understand what is going on. I have also read some introductions to the perl interpreter.

To know the use of the

Value Stack

This stack stores the values that regular perl code is operating on, usually intermediate values of expressions within a statement. The stack itself is formed of an array of SV pointers.

for the transfer of parameters to and return values from subroutines, helps me to build my model.

Yes, that's pretty much also my mental model, I'm glad I helped you.

And rest assured many people have (unfortunately) a different one. :/

I wished it was better communicated.

Part of the problem is that Perl is advertising itself as kind of a natural language with a lot of DWIM and idiomatic constructs, which shows in the style of the docs.

But at the end you need to communicate the technical basics in a clear, concise and orthogonal way to avoid confusion and frustration thru perceived ambiguities.

Much potential is wasted here...

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}