SEND + MORE = MONEY, see http://blog.plover.com/prog/haskell/monad-search.html

sendmore-perl5-version.pl

use v5.10;
use strict;
use warnings;

sub choose {
    my ($choices_ref, $fn) = @_;
    my @choices = @$choices_ref;
    for my $value (@choices) {
        $fn->($value);
    }
}
 
sub guard {
    my ($condition, $fn) = @_;
    if ($condition) {
        $fn->();
    }
}

sub minus {
    my ($set_ref, @remove) = @_;
    my @set = @$set_ref;
    my %remove = map { $_ => 1 } @remove;
    return [grep { !$remove{$_} } @set];
}

sub base_10 {
    my (@digits) = @_;
    my $result = 0;
    while (@digits) {
        my $digit = shift @digits;
        $result *= 10;
        $result += $digit;
    }
    return $result;
}

my @digits = 0..9;

choose minus(\@digits, 0), sub { my $s = shift;
choose minus(\@digits, $s), sub { my $e = shift;
choose minus(\@digits, $s, $e), sub { my $n = shift;
choose minus(\@digits, $s, $e, $n), sub { my $d = shift;
my $send = base_10($s, $e, $n, $d);
 
choose minus(\@digits, 0, $s, $e, $n, $d), sub { my $m = shift;
choose minus(\@digits, $s, $e, $n, $d, $m), sub { my $o = shift;
choose minus(\@digits, $s, $e, $n, $d, $m, $o), sub { my $r = shift;
my $more = base_10($m, $o, $r, $e);
 
choose minus(\@digits, $s, $e, $n, $d, $m, $o, $r), sub { my $y = shift;
my $money = base_10($m, $o, $n, $e, $y);
 
guard $send + $more == $money, sub {
say "$send + $more == $money";
}}}}}}}}};

sendmore-profiling-version.p6

my @digits = 0..9;

my $ITERATIONS = 10000;    # this line added for profiling

choose @digits ∖ 0, -> $s {
choose @digits ∖ $s, -> $e {
choose @digits ∖ ($s, $e), -> $n {
choose @digits ∖ ($s, $e, $n), -> $d {
my $send = :10[$s, $e, $n, $d];

choose @digits ∖ (0, $s, $e, $n, $d), -> $m {
choose @digits ∖ ($s, $e, $n, $d, $m), -> $o {
choose @digits ∖ ($s, $e, $n, $d, $m, $o), -> $r {
my $more = :10[$m, $o, $r, $e];

choose @digits ∖ ($s, $e, $n, $d, $m, $o, $r), -> $y {
my $money = :10[$m, $o, $n, $e, $y];

exit unless $ITERATIONS--;    # this line added for profiling

guard $send + $more == $money, {
say "$send + $more == $money";
}}}}}}}}};

sub choose(Set $choices, &fn) {
    for @$choices -> $value {
        &fn($value);
    }
}

sub guard($condition, &fn) {
    if $condition {
        &fn();
    }
}

sendmore.p6

my @digits = 0..9;

choose @digits ∖ 0, -> $s {
choose @digits ∖ $s, -> $e {
choose @digits ∖ ($s, $e), -> $n {
choose @digits ∖ ($s, $e, $n), -> $d {
my $send = :10[$s, $e, $n, $d];

choose @digits ∖ (0, $s, $e, $n, $d), -> $m {
choose @digits ∖ ($s, $e, $n, $d, $m), -> $o {
choose @digits ∖ ($s, $e, $n, $d, $m, $o), -> $r {
my $more = :10[$m, $o, $r, $e];

choose @digits ∖ ($s, $e, $n, $d, $m, $o, $r), -> $y {
my $money = :10[$m, $o, $n, $e, $y];

guard $send + $more == $money, {
say "$send + $more == $money";
}}}}}}}}};

sub choose(Set $choices, &fn) {
    for @$choices -> $value {
        &fn($value);
    }
}

sub guard($condition, &fn) {
    if $condition {
        &fn();
    }
}