Start on day 10 article

misc/perl6advent-2010/articles/feed.pod

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+=head1 Day 10 - Feed operators
+
+Anyone who has programmed in Perl 5 for a while has probably run across
+or written code similar to this:
+
+    my @new = sort { ... } map { ... } grep { ... } @original;
+
+In this construction, the data flows from the C<@original> array which
+feeds into the C<grep>, and that, in turn, feeds into the C<map>, and
+then into the C<sort>, and then finally, the result is assigned to the
+C<@new> array. Because they each take a list as their final
+parameter, simply by juxtposition, the data feeds from one operation
+to the next.
+
+Perl 6, on the other hand, makes this idea of data flowing from one
+operation to another explicit by introducing the I<feed operator>. The
+above Perl 5 code would be written like this in Perl 6:
+
+    my @new <== sort { ... } <== map { ... } <== grep { ... } <== @original;
+
+So, what do we gain from this? Normally, when reading code, you read
+from left to right. In the original Perl 5 code you would read from left
+to right until you realize that you're dealing with constructions where
+the direction of flow is right to left, then you jump to the end and
+follow the processing in a right-to-left manner. In Perl 6 there is now
+a prominent syntactic marker that clues you in to the leftward flowing
+nature of the data.
+
+Still, the right-to-left nature of this code is somewhat troublesome.
+It may not seem so onerous if all of the code fits on one line as
+above. But imagine if the blocks associated with C<grep>, C<map>, and
+C<sort> were little longer. Finding the end of the statement could be a
+bit annoying.
+
+Luckily, Perl 6 has another feed operator that allows you to write the
+same statement in a left-to-right fashion:
+
+    @original ==> grep { ... } ==> map { ... } ==> sort { ... }  ==> my @new;
+
+