X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperllol.pod;h=c348ec43b2bbe24f6f878eaf6f4f1facd5d141e6;hb=4447dfc12157eb387a12bf297bbc4f4c8c49a7a6;hp=a1e8a2deef10dea5ba9bf159cf3a667865c1e624;hpb=4d9142afa100a96f07b67cd4b087273df8c60543;p=p5sagit%2Fp5-mst-13.2.git

diff --git a/pod/perllol.pod b/pod/perllol.pod
index a1e8a2d..c348ec4 100644
--- a/pod/perllol.pod
+++ b/pod/perllol.pod
@@ -1,64 +1,64 @@
 =head1 NAME
 
-perlLoL - Manipulating Lists of Lists in Perl
+perllol - Manipulating Arrays of Arrays in Perl
 
 =head1 DESCRIPTION
 
-=head1 Declaration and Access of Lists of Lists
+=head2 Declaration and Access of Arrays of Arrays
 
-The simplest thing to build is a list of lists (sometimes called an array
-of arrays).  It's reasonably easy to understand, and almost everything
-that applies here will also be applicable later on with the fancier data
-structures.
+The simplest thing to build is an array of arrays (sometimes imprecisely
+called a list of lists).  It's reasonably easy to understand, and
+almost everything that applies here will also be applicable later
+on with the fancier data structures.
 
-A list of lists, or an array of an array if you would, is just a regular
-old array @LoL that you can get at with two subscripts, like $LoL[3][2].  Here's
-a declaration of the array:
+An array of an array is just a regular old array @AoA that you can
+get at with two subscripts, like C<$AoA[3][2]>.  Here's a declaration
+of the array:
 
-    # assign to our array a list of list references
-    @LoL = ( 
+    # assign to our array, an array of array references
+    @AoA = (
 	   [ "fred", "barney" ],
 	   [ "george", "jane", "elroy" ],
 	   [ "homer", "marge", "bart" ],
     );
 
-    print $LoL[2][2];
+    print $AoA[2][2];
   bart
 
 Now you should be very careful that the outer bracket type
-is a round one, that is, parentheses.  That's because you're assigning to
-an @list, so you need parens.  If you wanted there I<not> to be an @LoL,
+is a round one, that is, a parenthesis.  That's because you're assigning to
+an @array, so you need parentheses.  If you wanted there I<not> to be an @AoA,
 but rather just a reference to it, you could do something more like this:
 
-    # assign a reference to list of list references
-    $ref_to_LoL = [
+    # assign a reference to array of array references
+    $ref_to_AoA = [
 	[ "fred", "barney", "pebbles", "bambam", "dino", ],
 	[ "homer", "bart", "marge", "maggie", ],
-	[ "george", "jane", "alroy", "judy", ],
+	[ "george", "jane", "elroy", "judy", ],
     ];
 
-    print $ref_to_LoL->[2][2];
+    print $ref_to_AoA->[2][2];
 
-Notice that the outer bracket type has changed, and so our access syntax 
+Notice that the outer bracket type has changed, and so our access syntax
 has also changed.  That's because unlike C, in perl you can't freely
-interchange arrays and references thereto.  $ref_to_LoL is a reference to an 
-array, whereas @LoL is an array proper.  Likewise, $LoL[2] is not an 
+interchange arrays and references thereto.  $ref_to_AoA is a reference to an
+array, whereas @AoA is an array proper.  Likewise, C<$AoA[2]> is not an
 array, but an array ref.  So how come you can write these:
 
-    $LoL[2][2]
-    $ref_to_LoL->[2][2]
+    $AoA[2][2]
+    $ref_to_AoA->[2][2]
 
 instead of having to write these:
 
-    $LoL[2]->[2]
-    $ref_to_LoL->[2]->[2]
+    $AoA[2]->[2]
+    $ref_to_AoA->[2]->[2]
 
 Well, that's because the rule is that on adjacent brackets only (whether
-square or curly), you are free to omit the pointer dereferencing array.
+square or curly), you are free to omit the pointer dereferencing arrow.
 But you cannot do so for the very first one if it's a scalar containing
-a reference, which means that $ref_to_LoL always needs it.
+a reference, which means that $ref_to_AoA always needs it.
 
-=head1 Growing Your Own
+=head2 Growing Your Own
 
 That's all well and good for declaration of a fixed data structure,
 but what if you wanted to add new elements on the fly, or build
@@ -67,181 +67,171 @@ it up entirely from scratch?
 First, let's look at reading it in from a file.  This is something like
 adding a row at a time.  We'll assume that there's a flat file in which
 each line is a row and each word an element.  If you're trying to develop an
-@LoL list containing all these, here's the right way to do that:
+@AoA array containing all these, here's the right way to do that:
 
     while (<>) {
 	@tmp = split;
-	push @LoL, [ @tmp ];
-    } 
+	push @AoA, [ @tmp ];
+    }
 
 You might also have loaded that from a function:
 
     for $i ( 1 .. 10 ) {
-	$LoL[$i] = [ somefunc($i) ];
+	$AoA[$i] = [ somefunc($i) ];
     }
 
 Or you might have had a temporary variable sitting around with the
-list in it.  
+array in it.
 
     for $i ( 1 .. 10 ) {
 	@tmp = somefunc($i);
-	$LoL[$i] = [ @tmp ];
+	$AoA[$i] = [ @tmp ];
     }
 
-It's very important that you make sure to use the C<[]> list reference
+It's very important that you make sure to use the C<[]> array reference
 constructor.  That's because this will be very wrong:
 
-    $LoL[$i] = @tmp;
+    $AoA[$i] = @tmp;
 
-You see, assigning a named list like that to a scalar just counts the 
-number of elements in @tmp, which probably isn't what you want.  
+You see, assigning a named array like that to a scalar just counts the
+number of elements in @tmp, which probably isn't what you want.
 
 If you are running under C<use strict>, you'll have to add some
 declarations to make it happy:
 
     use strict;
-    my(@LoL, @tmp);
+    my(@AoA, @tmp);
     while (<>) {
 	@tmp = split;
-	push @LoL, [ @tmp ];
-    } 
+	push @AoA, [ @tmp ];
+    }
 
 Of course, you don't need the temporary array to have a name at all:
 
     while (<>) {
-	push @LoL, [ split ];
-    } 
+	push @AoA, [ split ];
+    }
 
 You also don't have to use push().  You could just make a direct assignment
 if you knew where you wanted to put it:
 
-    my (@LoL, $i, $line);
-    for $i ( 0 .. 10 ) 
+    my (@AoA, $i, $line);
+    for $i ( 0 .. 10 ) {
 	$line = <>;
-	$LoL[$i] = [ split ' ', $line ];
-    } 
+	$AoA[$i] = [ split ' ', $line ];
+    }
 
 or even just
 
-    my (@LoL, $i);
-    for $i ( 0 .. 10 ) 
-	$LoL[$i] = [ split ' ', <> ];
-    } 
+    my (@AoA, $i);
+    for $i ( 0 .. 10 ) {
+	$AoA[$i] = [ split ' ', <> ];
+    }
 
-You should in general be leery of using potential list functions
-in a scalar context without explicitly stating such.  
-This would be clearer to the casual reader:
+You should in general be leery of using functions that could
+potentially return lists in scalar context without explicitly stating
+such.  This would be clearer to the casual reader:
 
-    my (@LoL, $i);
-    for $i ( 0 .. 10 ) 
-	$LoL[$i] = [ split ' ', scalar(<>) ];
-    } 
+    my (@AoA, $i);
+    for $i ( 0 .. 10 ) {
+	$AoA[$i] = [ split ' ', scalar(<>) ];
+    }
 
-If you wanted to have a $ref_to_LoL variable as a reference to an array,
+If you wanted to have a $ref_to_AoA variable as a reference to an array,
 you'd have to do something like this:
 
     while (<>) {
-	push @$ref_to_LoL, [ split ];
-    } 
-
-Actually, if you were using strict, you'd not only have to declare $ref_to_LoL as
-you had to declare @LoL, but you'd I<also> having to initialize it to a
-reference to an empty list.  (This was a bug in 5.001m that's been fixed
-for the 5.002 release.)
-
-    my $ref_to_LoL = [];
-    while (<>) {
-	push @$ref_to_LoL, [ split ];
-    } 
+	push @$ref_to_AoA, [ split ];
+    }
 
-Ok, now you can add new rows.  What about adding new columns?  If you're
-just dealing with matrices, it's often easiest to use simple assignment:
+Now you can add new rows.  What about adding new columns?  If you're
+dealing with just matrices, it's often easiest to use simple assignment:
 
     for $x (1 .. 10) {
 	for $y (1 .. 10) {
-	    $LoL[$x][$y] = func($x, $y);
+	    $AoA[$x][$y] = func($x, $y);
 	}
     }
 
     for $x ( 3, 7, 9 ) {
-	$LoL[$x][20] += func2($x);
-    } 
+	$AoA[$x][20] += func2($x);
+    }
 
-It doesn't matter whether those elements are already 
+It doesn't matter whether those elements are already
 there or not: it'll gladly create them for you, setting
 intervening elements to C<undef> as need be.
 
-If you just wanted to append to a row, you'd have
+If you wanted just to append to a row, you'd have
 to do something a bit funnier looking:
 
     # add new columns to an existing row
-    push @{ $LoL[0] }, "wilma", "betty";
+    push @{ $AoA[0] }, "wilma", "betty";
 
-Notice that I I<couldn't> just say:
+Notice that I I<couldn't> say just:
 
-    push $LoL[0], "wilma", "betty";  # WRONG!
+    push $AoA[0], "wilma", "betty";  # WRONG!
 
 In fact, that wouldn't even compile.  How come?  Because the argument
 to push() must be a real array, not just a reference to such.
 
-=head1 Access and Printing
+=head2 Access and Printing
 
-Now it's time to print your data structure out.  How 
-are you going to do that?  Well, if you only want one
+Now it's time to print your data structure out.  How
+are you going to do that?  Well, if you want only one
 of the elements, it's trivial:
 
-    print $LoL[0][0];
+    print $AoA[0][0];
 
 If you want to print the whole thing, though, you can't
-just say 
+say
 
-    print @LoL;		# WRONG
+    print @AoA;		# WRONG
 
-because you'll just get references listed, and perl will never
-automatically dereference things for you.  Instead, you have to 
+because you'll get just references listed, and perl will never
+automatically dereference things for you.  Instead, you have to
 roll yourself a loop or two.  This prints the whole structure,
 using the shell-style for() construct to loop across the outer
-set of subscripts.  
+set of subscripts.
 
-    for $aref ( @LoL ) {
+    for $aref ( @AoA ) {
 	print "\t [ @$aref ],\n";
     }
 
 If you wanted to keep track of subscripts, you might do this:
 
-    for $i ( 0 .. $#LoL ) {
-	print "\t elt $i is [ @{$LoL[$i]} ],\n";
+    for $i ( 0 .. $#AoA ) {
+	print "\t elt $i is [ @{$AoA[$i]} ],\n";
     }
 
 or maybe even this.  Notice the inner loop.
 
-    for $i ( 0 .. $#LoL ) {
-	for $j ( 0 .. $#{$LoL[$i]} ) {
-	    print "elt $i $j is $LoL[$i][$j]\n";
+    for $i ( 0 .. $#AoA ) {
+	for $j ( 0 .. $#{$AoA[$i]} ) {
+	    print "elt $i $j is $AoA[$i][$j]\n";
 	}
     }
 
-As you can see, it's getting a bit complicated.  That's why 
+As you can see, it's getting a bit complicated.  That's why
 sometimes is easier to take a temporary on your way through:
 
-    for $i ( 0 .. $#LoL ) {
-	$aref = $LoL[$i];
+    for $i ( 0 .. $#AoA ) {
+	$aref = $AoA[$i];
 	for $j ( 0 .. $#{$aref} ) {
-	    print "elt $i $j is $LoL[$i][$j]\n";
+	    print "elt $i $j is $AoA[$i][$j]\n";
 	}
     }
 
-Hm... that's still a bit ugly.  How about this:
+Hmm... that's still a bit ugly.  How about this:
 
-    for $i ( 0 .. $#LoL ) {
-	$aref = $LoL[$i];
+    for $i ( 0 .. $#AoA ) {
+	$aref = $AoA[$i];
 	$n = @$aref - 1;
 	for $j ( 0 .. $n ) {
-	    print "elt $i $j is $LoL[$i][$j]\n";
+	    print "elt $i $j is $AoA[$i][$j]\n";
 	}
     }
 
-=head1 Slices
+=head2 Slices
 
 If you want to get at a slice (part of a row) in a multidimensional
 array, you're going to have to do some fancy subscripting.  That's
@@ -250,56 +240,56 @@ pointer arrow for dereferencing, no such convenience exists for slices.
 (Remember, of course, that you can always write a loop to do a slice
 operation.)
 
-Here's how to do one operation using a loop.  We'll assume an @LoL
+Here's how to do one operation using a loop.  We'll assume an @AoA
 variable as before.
 
     @part = ();
-    $x = 4; 	
+    $x = 4;
     for ($y = 7; $y < 13; $y++) {
-	push @part, $LoL[$x][$y];
-    } 
+	push @part, $AoA[$x][$y];
+    }
 
 That same loop could be replaced with a slice operation:
 
-    @part = @{ $LoL[4] } [ 7..12 ];
+    @part = @{ $AoA[4] } [ 7..12 ];
 
 but as you might well imagine, this is pretty rough on the reader.
 
 Ah, but what if you wanted a I<two-dimensional slice>, such as having
-$x run from 4..8 and $y run from 7 to 12?  Hm... here's the simple way:
+$x run from 4..8 and $y run from 7 to 12?  Hmm... here's the simple way:
 
-    @newLoL = ();
+    @newAoA = ();
     for ($startx = $x = 4; $x <= 8; $x++) {
-	for ($starty = $y = 7; $x <= 12; $y++) {
-	    $newLoL[$x - $startx][$y - $starty] = $LoL[$x][$y];
+	for ($starty = $y = 7; $y <= 12; $y++) {
+	    $newAoA[$x - $startx][$y - $starty] = $AoA[$x][$y];
 	}
-    } 
+    }
 
-We can reduce some of the looping through slices 
+We can reduce some of the looping through slices
 
     for ($x = 4; $x <= 8; $x++) {
-	push @newLoL, [ @{ $LoL[$x] } [ 7..12 ] ];
+	push @newAoA, [ @{ $AoA[$x] } [ 7..12 ] ];
     }
 
 If you were into Schwartzian Transforms, you would probably
 have selected map for that
 
-    @newLoL = map { [ @{ $LoL[$_] } [ 7..12 ] ] } 4 .. 8;
+    @newAoA = map { [ @{ $AoA[$_] } [ 7..12 ] ] } 4 .. 8;
 
 Although if your manager accused of seeking job security (or rapid
 insecurity) through inscrutable code, it would be hard to argue. :-)
 If I were you, I'd put that in a function:
 
-    @newLoL = splice_2D( \@LoL, 4 => 8, 7 => 12 );
+    @newAoA = splice_2D( \@AoA, 4 => 8, 7 => 12 );
     sub splice_2D {
-	my $lrr = shift; 	# ref to list of list refs!
-	my ($x_lo, $x_hi, 
+	my $lrr = shift; 	# ref to array of array refs!
+	my ($x_lo, $x_hi,
 	    $y_lo, $y_hi) = @_;
 
-	return map { 
-	    [ @{ $lrr->[$_] } [ $y_lo .. $y_hi ] ] 
+	return map {
+	    [ @{ $lrr->[$_] } [ $y_lo .. $y_hi ] ]
 	} $x_lo .. $x_hi;
-    } 
+    }
 
 
 =head1 SEE ALSO
@@ -308,6 +298,6 @@ perldata(1), perlref(1), perldsc(1)
 
 =head1 AUTHOR
 
-Tom Christiansen <tchrist@perl.com>
+Tom Christiansen <F<tchrist@perl.com>>
 
-Last udpate: Sat Oct  7 19:35:26 MDT 1995
+Last update: Thu Jun  4 16:16:23 MDT 1998