NAME

       Catmandu::Fix::Bind - a wrapper for Catmandu::Fix-es

SYNOPSIS

         package Catmandu::Fix::Bind::demo;
         use Moo;
         with 'Catmandu::Fix::Bind';

         sub bind {
           my ($self,$data,$code,$name) = @_;
           warn "executing $name";
           $code->($data);
         }

         # in your fix script you can now write
         do
            demo()

            fix1()
            fix2()
            fix3()
         end

         # this will execute all the fixes as expected, and print to STDERR the following messages

         executing fix1
         executing fix2
         executing fix3

DESCRIPTION

       Bind is a package that wraps Catmandu::Fix-es and other Catmandu::Bind-s together. This
       gives the programmer further control on the excution of fixes. With Catmandu::Fix::Bind
       you can simulate the 'before', 'after' and 'around' modifiers as found in Moo or Dancer.

       To wrap Fix functions, the Fix language introduces the 'do' statement:

         do BIND
            FIX1
            FIX2
            FIX3
         end

       where BIND is a implementation of Catmandu::Fix::Bind and FIX1,...,FIXn are Catmandu::Fix
       functions.

       In the example above the BIND will wrap FIX1, FIX2 and FIX3. BIND will first wrap the
       record data using its 'unit' method and send the data sequentially to each FIX which can
       make inline changes to the record data. In pseudo-code this will look like:

         $bind_data = $bind->unit($data);
         $bind_data = $bind->bind($bind_data, $fix1);
         $bind_data = $bind->bind($bind_data, $fix2);
         $bind_data = $bind->bind($bind_data, $fix3);
         return $data;

        An alternative form exists, 'doset' which will overwrite the record data with results of the last
        fix.

         doset BIND
               FIX1
               FIX2
               FIX3
         end

       Will result in a pseudo code like:

         $bind_data = $bind->unit($data);
         $bind_data = $bind->bind($bind_data, $fix1);
         $bind_data = $bind->bind($bind_data, $fix2);
         $bind_data = $bind->bind($bind_data, $fix3);
         return $bind_data;

       A Catmandu::Fix::Bind needs to implement two methods: 'unit' and 'bind'.

METHODS

   unit($data)
       The unit method receives a Perl $data HASH and should return it, possibly converted to a
       new type.  The 'unit' method is called before all Fix methods are executed. A trivial, but
       verbose, implementation of 'unit' is:

         sub unit {
             my ($self,$data) = @_;
             my $wrapped_data = $data;
             return $wrapped_data;
         }

   bind($wrapped_data,$code)
       The bind method is executed for every Catmandu::Fix method in the fix script. It receives
       the $wrapped_data (wrapped by 'unit'), the fix method as anonymous subroutine and the name
       of the fix. It should return data with the same type as returned by 'unit'.  A trivial,
       but verbose, implementaion of 'bind' is:

         sub bind {
           my ($self,$wrapped_data,$code) = @_;
           my $data = $wrapped_data;
           $data = $code->($data);
           # we don't need to wrap it again because the $data and $wrapped_data have the same type
           $data;
         }

REQUIREMENTS

       Bind modules are simplified implementations of Monads. They should answer the formal
       definition of Monads, codified in 3 monadic laws:

   left unit: unit acts as a neutral element of bind
          my $monad = Catmandu::Fix::Bind->demo();

          # bind(unit(data), coderef) == unit(coderef(data))
          $monad->bind( $monad->unit({foo=>'bar'}) , $coderef) == $monad->unit($coderef->({foo=>'bar'}));

   right unit: unit act as a neutral element of bind
          # bind(unit(data), unit) == unit(data)
          $monad->bind( $monad->unit({foo=>'bar'}) , sub { $monad->unit(shift) } ) == $monad->unit({foo=>'bar'});

   associative: chaining bind blocks should have the same effect as nesting them
          # bind(bind(unit(data),f),g) == bind(unit(data), sub { return bind(unit(f(data)),g) } )
          my $f = sub { my $data = shift; $data->{demo} = 1 ; $data };
          my $g = sub { my $data = shift; $data->{demo} += 1 ; $data};

          $monad->bind( $monad->bind( $monad->unit({}) , f ) , g ) ==
            $monad->bind( $monad->unit({}) , sub { my $data = shift; $monad->bind($monad->unit($f->($data)), $g ); $data; });

SEE ALSO

       Catmandu::Fix::Bind::identity, Catmandu::Fix::Bind::benchmark