Scheme PHP [Source Code]
looking
function looking
($s, $l)
{return
    keep_looking($s, pick(1, $l), $l);
}
keep-looking [1]
function keep_looking
($s, $sorn, $l)
{return
    is_number($sorn) ? keep_looking($s, pick($sorn, $l), $l)
    : is_eq($sorn, $s);
}
eternity
function eternity
($x)
{return
    eternity($x);
}
shift
function shift
($pair)
{return
    build(first(first($pair)), 
          build(second(first($pair)), 
                second($pair)));
}
align
function align
($pora)
{return
    is_atom($pora) ? $pora 
    : (is_pair(first($pora)) ? align(shift($pora))
      : build(first($pora), align(second($pora))));
}
length*
function length_star
($pora)
{return
    is_atom($pora) ? 1
    : plus(length_star(first($pora)), length_star(second($pora)));
}
weight*
function weight_star
($pora)
{return
    is_atom($pora) ? 1
    : plus(x(weight_star(first($pora)), 2), 
             weight_star(second($pora)));
}
shuffle
function shuffle
($pora) 
{return
    is_atom($pora) ? $pora
    : (is_pair(first($pora)) ? shuffle(revpair($pora))
      : build(first($pora), shuffle(second($pora))));
}
C [2]
function C
($n)
{return
    is_one($n) ? 1
    : (is_even($n) ? C(division($n, 2))
      : C(add1(x(3, $n))));
}
A [3], [4], [5]
function A
($n, $m)
{return
    is_zero($n) ? add1($m)
    : (is_zero($m) ? A(sub1($n), 1)
      : A(sub1($n), A($n, sub1($m))));
}
Y [6]
function Y
($le)
{return
    (function ($f) 
     {return
        $f($f);
     })(function ($f) use ($le) 
        {return
            $le(function ($x) use ($f) 
                {return
                    $f($f)($x);
                });
        });
}
[7]
  1. Partial function/Total function
  2. Lothar Collatz
  3. Wilhelm Ackermann
  4. Kurt Gödel
  5. Alan Turing
  6. Y Combinator
  7. Y Combinator in PHP