some more examples

[gitmo/Moose-Autobox.git] / lib / Moose / Autobox / Code.pm

diff --git a/lib/Moose/Autobox/Code.pm b/lib/Moose/Autobox/Code.pm
index 0dabc53..c2e33a1 100644 (file)
--- a/lib/Moose/Autobox/Code.pm
+++ b/lib/Moose/Autobox/Code.pm
@@ -32,11 +32,17 @@ sub conjoin {
        return sub { $f->(@_) && $f2->(@_) }    
 }
 
-#sub dump {
-    #my ($self) = @_;
-    #require Data::Dump::Streamer;
-    #return Data::Dump::Streamer::Dump($self)->Out();
-#}
+# fixed point combinators
+
+sub u {
+    my $f = shift;
+    sub { $f->($f, @_) };
+}
+
+sub y {
+    my $f = shift;
+    (sub { my $h = shift; sub { $f->(($h->u)->())->(@_) } }->u)->();
+}
 
 1;
 
@@ -51,12 +57,25 @@ Moose::Autobox::Code - the Code role
 =head1 SYNOPOSIS
 
   use Moose::Autobox;
-  use autobox;
   
   my $adder = sub { $_[0] + $_[1] };
   my $add_2 = $adder->curry(2);
   
   $add_2->(2); # returns 4
+  
+  # create a recursive subroutine 
+  # using the Y combinator
+  *factorial = sub {
+      my $f = shift;
+      sub {
+          my $n = shift;
+          return 1 if $n < 2;
+          return $n * $f->($n - 1);
+      }
+  }->y;
+  
+  factorial(10) # returns 3628800
+  
 
 =head1 DESCRIPTION
 
@@ -79,6 +98,14 @@ This is a role to describe operations on the Code type.
 This will take a list of C<@subs> and compose them all into a single 
 subroutine where the output of one sub will be the input of another. 
 
+=item B<y>
+
+This implements the Y combinator.
+
+=item B<u>
+
+This implements the U combinator.
+
 =back
 
 =over 4
@@ -87,6 +114,16 @@ subroutine where the output of one sub will be the input of another.
 
 =back
 
+=head1 SEE ALSO
+
+=over 4
+
+=item L<http://en.wikipedia.org/wiki/Fixed_point_combinator>
+
+=item L<http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/20469>
+
+=back
+
 =head1 BUGS
 
 All complex software has bugs lurking in it, and this module is no