#! perl -slw
use strict;
use Carp;
use Data::Dump qw[ pp ];

sub hmap (&@) {
    our( $a, $b );
    my $code = shift;
    croak "Even sized list or hash ref required"
        if @_ & 1 and not @_ == 1 && ref( $_[0] ) =~ m[HASH];

    @_ = %{ $_[0] } if @_ == 1;
    my @rv;
    while( @_ ) {
        local( $a, $b ) = splice( @_, 0, 2 ),
        my $rv = $code->( $a, local $_ = $b );
        push @rv, $rv ? ( $a, $rv ) : ();
    }
    wantarray ? @rv : { @rv };
}

sub hgrep (&%) {
    our( $a, $b );
    my $code = shift;
    croak "Even sized list or hash ref required"
        if @_ & 1 and not @_ == 1 && ref( $_[0] ) =~ m[HASH];

    @_ = %{ $_[0] } if @_ == 1;
    my @rv;
    while(  @_ ) {
        local( $a, $b ) = splice( @_, 0, 2 );
        my $rv = $code->( $a, local $_ = $b);
        push @rv, $rv ? ( $a, $b ) : ();
    }
    wantarray ? @rv : { @rv };
}

my %h = ( 'a' .. 'j', 's' .. 'z' );
pp 'start: ', \%h;

my %r1 = hmap{ ++$b } %h;
pp 'incr values: ', \%r1;

my $r2 = hmap{ ++$_ } %r1;
pp 'and again: ', $r2;

my %h3 = hmap{ ++$_[1] } $r2;
pp 'and once more: ', \%h3;

my %s = hgrep{ $a le 'm' } %h;
pp 'filter keys le m: ', \%s;

my $t = hgrep{ length $b > 1 } \%h3;
pp 'filter values longer than 1 char: ', $t;

print "\n-----------\n";

my %old = (
    '1' => { 'nick' => 'rbush', 'bday' => '3/12/1965', 'phone' => '5551212'   },
    '5' => { 'nick' => 'fred',  'bday' => '5/01/1972', 'phone' => '1112300'   },
    '11'=> { 'nick' => 'joan',  'bday' => '1/02/2033', 'phone' => '123456789' },
);

my %new = hmap {
    exists $b->{ nick } && $b->{ nick } =~ m[^(?:rbush|fred)$]
        ? ( $a => scalar hgrep{ $a =~ m[^(nick|phone)$] } $b ) : ()
} \%old;

pp \%new;

__END__
c:\test>hmap
(
  "start: ",
  { a => "b", c => "d", e => "f", g => "h", i => "j", "s" => "t", u => "v", w => "x", "y" => "z" },
)

(
  "incr values: ",
  { a => "c", c => "e", e => "g", g => "i", i => "k", "s" => "u", u => "w", w => "y", "y" => "aa" },
)

(
  "and again: ",
  { a => "d", c => "f", e => "h", g => "j", i => "l", "s" => "v", u => "x", w => "z", "y" => "ab" },
)

(
  "and once more: ",
  { a => "e", c => "g", e => "i", g => "k", i => "m", "s" => "w", u => "y", w => "aa", "y" => "ac" },
)

(
  "filter keys le m: ",
  { a => "b", c => "d", e => "f", g => "h", i => "j" },
)

(
  "filter values longer than 1 char: ",
  { w => "aa", "y" => "ac" },
)


-----------

{
  1 => { nick => "rbush", phone => 5551212 },
  5 => { nick => "fred", phone => 1112300 },
}