In common with others, I'm not sure how this question relates to your OP ([ 3,2,2,3,3,3,1 ] doesn't look like a linked list to me, either), but I can answer your specific questions.

... what exact data type [is] $L ...

$L is a scalar. This is determined by the $ sigil before the symbol.

... how [does] the data set get passed into @_ and assigned to $L.

The expression  [ 3,2,2,3,3,3,1 ] returns a reference (to an array). A reference is always a scalar value even though the referent, e.g., an array or hash, is not. A scalar is passed to a subroutine in the usual way: 

c:\@Work\Perl>perl -wMstrict -le
"my $arrayref = [ 3,2,2,3,3,3,1 ];
 ;;
 sub func {
   my ($msg, $ar) = @_;
   ;;
   printf qq{$msg: scalar ref: $ar };
   printf qq{'$_' } for @$ar;
   printf qq{(%d elements) \n}, scalar @$ar;
   }
 ;;
 func('A', [ 9, 8, 7 ]);
 func('B', $arrayref);
"
A: scalar ref: ARRAY(0x1cb226c) '9' '8' '7' (3 elements)
B: scalar ref: ARRAY(0x6fd05c) '3' '2' '2' '3' '3' '3' '1' (7 elements
+)

[download]

Update: Changed code example: added element count. Slight wording change.

Give a man a fish:  <%-(-(-(-<

In reply to Re^3: Nodes count in Linked List by AnomalousMonk
in thread Perl linked list by Perl_is_Perl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.