Task: Ternary logic
C++: #include <iostream>
#include <stdlib.h>

class trit {
public:
    static const trit False, Maybe, True;

    trit operator !() const {
        return static_cast<Value>(-value);
    }

    trit operator &&(const trit &b) const {
        return (value < b.value) ? value : b.value;
    }

    trit operator ||(const trit &b) const {
        return (value > b.value) ? value : b.value;
    }

    trit operator >>(const trit &b) const {
        return -value > b.value ? static_cast<Value>(-value) : b.value;
    }

    trit operator ==(const trit &b) const {
        return static_cast<Value>(value * b.value);
    }

    char chr() const {
        return "F?T"[value + 1];
    }

protected:
    typedef enum { FALSE=-1, MAYBE, TRUE } Value;

    Value value;

    trit(const Value value) : value(value) { }
};

std::ostream& operator<<(std::ostream &os, const trit &t)
{
    os << t.chr();
    return os;
}

const trit trit::False = trit(trit::FALSE);
const trit trit::Maybe = trit(trit::MAYBE);
const trit trit::True = trit(trit::TRUE);

int main(int, char**) {
    const trit trits[3] = { trit::True, trit::Maybe, trit::False };

#define for_each(name) \
    for (size_t name=0; name<3; ++name)

#define show_op(op) \
    std::cout << std::endl << #op << " "; \
    for_each(a) std::cout << ' ' << trits[a]; \
    std::cout << std::endl << "  -------"; \
    for_each(a) { \
        std::cout << std::endl << trits[a] << " |"; \
        for_each(b) std::cout << ' ' << (trits[a] op trits[b]); \
    } \
    std::cout << std::endl;

    std::cout << "! ----" << std::endl;
    for_each(a) std::cout << trits[a] << " | " << !trits[a] << std::endl;

    show_op(&&);
    show_op(||);
    show_op(>>);
    show_op(==);
    return EXIT_SUCCESS;
}

PHP: #!/usr/bin/php
<?php

# defined as numbers, so I can use max() and min() on it
if (! define('triFalse',0))  trigger_error('Unknown error defining!', E_USER_ERROR);
if (! define('triMaybe',1))  trigger_error('Unknown error defining!', E_USER_ERROR);
if (! define('triTrue', 2))  trigger_error('Unknown error defining!', E_USER_ERROR);

$triNotarray = array(triFalse=>triTrue, triMaybe=>triMaybe, triTrue=>triFalse);

# output helper
function triString ($tri) {
    if ($tri===triFalse) return 'false  ';
    if ($tri===triMaybe) return 'unknown';
    if ($tri===triTrue)  return 'true   ';
    trigger_error('triString: parameter not a tri value', E_USER_ERROR);
}

function triAnd() {
    if (func_num_args() < 2) 
       trigger_error('triAnd needs 2 or more parameters', E_USER_ERROR);
    return min(func_get_args());
}

function triOr() {
    if (func_num_args() < 2) 
       trigger_error('triOr needs 2 or more parameters', E_USER_ERROR);
    return max(func_get_args());
}

function triNot($t) {
    global $triNotarray; # using result table
    if (in_array($t, $triNotarray)) return $triNotarray[$t];
    trigger_error('triNot: Parameter is not a tri value', E_USER_ERROR);
}

function triImplies($a, $b) {
    if ($a===triFalse || $b===triTrue)  return triTrue;
    if ($a===triMaybe || $b===triMaybe) return triMaybe;
    # without parameter type check I just would return triFalse here
    if ($a===triTrue &&  $b===triFalse) return triFalse;
    trigger_error('triImplies: parameter type error', E_USER_ERROR);
}

function triEquiv($a, $b) {
    if ($a===triTrue)  return $b;
    if ($a===triMaybe) return $a;
    if ($a===triFalse) return triNot($b);
    trigger_error('triEquiv: parameter type error', E_USER_ERROR);
}

# data sampling

printf("--- Sample output for a equivalent b ---\n\n");

foreach ([triTrue,triMaybe,triFalse] as $a) {
    foreach ([triTrue,triMaybe,triFalse] as $b) {
        printf("for a=%s and b=%s a equivalent b is %s\n",
               triString($a), triString($b), triString(triEquiv($a, $b)));
    }
}