#!/usr/bin/perl
use strict; use warnings; use autodie;
use Benchmark qw[ cmpthese ];

# operate on an array
my $fa_inc = sub { map {$_ + 1} @_ };
my $fa_log = sub { map {log $_} @_ };
my $fa_x3  = sub { map {$_ * 3} @_ };

# edit an array in place
my $fea_inc = sub { map {$_ = $_ + 1} @_ };
my $fea_log = sub { map {$_ = log $_} @_ };
my $fea_x3  = sub { map {$_ = $_ * 3} @_ };

# operate on a scalar
my $fs_inc = sub { 1 + shift };
my $fs_log = sub { log shift };
my $fs_x3  = sub { 3 * shift };

# operate on a scalar by reference
my $fsr_inc = sub { $_[0] + 1 };
my $fsr_log = sub { log $_[0] };
my $fsr_x3  = sub { $_[0] * 3 };

# edit a scalar in place
my $fser_inc = sub { $_[0] = $_[0] + 1 };
my $fser_log = sub { $_[0] = log $_[0] };
my $fser_x3  = sub { $_[0] = $_[0] * 3 };

my (@l1, @l2, @l3);
push @l1, 100*rand for 0 .. 1000;

sub t_fa {
    $fa_inc->($fa_log->($fa_x3->(@_)))
}

sub t_fea {
    @l3 = @_;
    $fea_inc->($fea_log->($fea_x3->(@l3)))
}

sub t_fs {
    map { $fs_inc->($fs_log->($fs_x3->($_))) } @_
}

sub t_fsr {
    map { $fsr_inc->($fsr_log->($fsr_x3->($_))) } @_
}

sub t_fser {
    @l3 = @_;
    map { $fser_inc->($fser_log->($fser_x3->($_))) } @l3;
}

# verify that they all have the same result
my (@t, @u);
@t = t_fa(@l1);

@u = t_fea(@l1);
cmp_array('fea', \@t, \@u);

@u = t_fs(@l1);
cmp_array('fea', \@t, \@u);

@u = t_fsr(@l1);
cmp_array('fea', \@t, \@u);

@u = t_fser(@l1);
cmp_array('fea', \@t, \@u);

sub cmp_array {
    my ($funcname, $ra1, $ra2) = @_;
    my ($la1, $la2) = ($#$ra1, $#$ra2);
    die "$funcname: Mismatched length! $la1 != $la2\n" 
      unless $la1 == $la2;
    for (0 .. $la1) {
        die "$funcname: Mismatch $_: $ra1->[$_] != $ra2->[$_]\n" 
          if $ra1->[$_] != $ra2->[$_];
    }
}

cmpthese -1, {
    fa   => q[ @l2 = t_fa(@l1)   ],
    fea  => q[ @l2 = t_fea(@l1)  ],
    fs   => q[ @l2 = t_fs(@l1)   ],
    fsr  => q[ @l2 = t_fsr(@l1)  ],
    fser => q[ @l2 = t_fser(@l1) ],
};

##</code><code>##

$ perl chain_transform.pl
         Rate  fea   fa fser  fsr   fs
fea  199110/s   --  -8% -60% -68% -69%
fa   216392/s   9%   -- -57% -66% -67%
fser 499367/s 151% 131%   -- -21% -23%
fsr  628278/s 216% 190%  26%   --  -4%
fs   651987/s 227% 201%  31%   4%   --