part 3

honeysql.php

<?php

$data = 
  [':select' => [':a', ':b', [':select' => [':c']]],
   ':from' => [':foo']];
  
  
function recur(array $map) : object {
  return new \RecursiveIteratorIterator(
    new \RecursiveArrayIterator($map),
    \RecursiveIteratorIterator::SELF_FIRST
  );
}
  
function map_to_sql(array &$sql, object $map) : array {

    // $map = recur($map);
    
    foreach ($map as $key => $result) {
        switch (TRUE) {
            case $key === ':select':
                var_dump($result);
                $sql[] = 'SELECT ' . implode(' ', $result); 
            break;
            case $key === ':from':
                $sql[] = 'FROM ' . implode(' ', $result);
            break;
         }
    }

    return $sql;
}

function has_key(object $map, string $key) : bool {
    return isset($map->{$key});
}

$sql = [];
$out = map_to_sql($sql, recur($data));
$out = implode("\n", $out);
var_dump($out);