Task: Ternary logic
C: #include <stdio.h>
 
typedef enum {
  TRITTRUE,  
  TRITMAYBE, 
  TRITFALSE  
} trit;
 

trit tritNot[3] = {TRITFALSE , TRITMAYBE, TRITTRUE};
trit tritAnd[3][3] = { {TRITTRUE, TRITMAYBE, TRITFALSE},
                       {TRITMAYBE, TRITMAYBE, TRITFALSE},
                       {TRITFALSE, TRITFALSE, TRITFALSE} };
 
trit tritOr[3][3] = { {TRITTRUE, TRITTRUE, TRITTRUE},
                      {TRITTRUE, TRITMAYBE, TRITMAYBE},
                      {TRITTRUE, TRITMAYBE, TRITFALSE} };
 
trit tritThen[3][3] = { { TRITTRUE, TRITMAYBE, TRITFALSE},
                        { TRITTRUE, TRITMAYBE, TRITMAYBE},
                        { TRITTRUE, TRITTRUE, TRITTRUE } };
 
trit tritEquiv[3][3] = { { TRITTRUE, TRITMAYBE, TRITFALSE},
                         { TRITMAYBE, TRITMAYBE, TRITMAYBE},
                         { TRITFALSE, TRITMAYBE, TRITTRUE } };



const char* tritString[3] = {"T", "?", "F"};

void demo_binary_op(trit operator[3][3], const char* name)
{
  trit operand1 = TRITTRUE; 
  trit operand2 = TRITTRUE; 

  
  printf("\n");

  
  for( operand1 = TRITTRUE; operand1 <= TRITFALSE; ++operand1 )
  {
    for( operand2 = TRITTRUE; operand2 <= TRITFALSE; ++operand2 )
    {
      printf("%s %s %s: %s\n", tritString[operand1],
                               name,
                               tritString[operand2],
                               tritString[operator[operand1][operand2]]);
    }
  }

}

int main()
{
  trit op1 = TRITTRUE; 
  trit op2 = TRITTRUE; 
 
  
  for( op1 = TRITTRUE; op1 <= TRITFALSE; ++op1 )
  {
    printf("Not %s: %s\n", tritString[op1], tritString[tritNot[op1]]);
  }
  demo_binary_op(tritAnd, "And");
  demo_binary_op(tritOr, "Or");
  demo_binary_op(tritThen, "Then");
  demo_binary_op(tritEquiv, "Equiv");

 
  return 0;
}

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)));
    }
}