public function testIsVariableEquals()
{
$var = variable(1);
$var2 = variable(1);
$var3 = variable(2);
$this->assertTrue(isVariableEquals($var, $var2));
$this->assertFalse(isVariableEquals($var2, $var3));
}
/**
* Unifies two terms in a substitution.
*
* @param Variable $u a variable
* @param mixed $v a term
* @param Cons $s the substitution
*/
function unify($u, $v, $s)
{
$u = walk($u, $s);
$v = walk($v, $s);
if (isVariable($u) && isVariable($v) && isVariableEquals($u, $v)) {
return $s;
} elseif (isVariable($u)) {
return extS($u, $v, $s);
} elseif (isVariable($v)) {
return extS($v, $u, $s);
} elseif (isPair($u) && isPair($v)) {
$s = unify(car($u), car($v), $s);
if ($s) {
return unify(cdr($u), cdr($v), $s);
}
} elseif ($u === $v) {
return $s;
}
}
