<?php
function search($array, $word, $word_so_far = '') {
    if ($word === $word_so_far) {
        return true;
    }
 
    foreach ($array as $symbol) {
        $new_word = $word_so_far . $symbol;
        if (substr($word, 0, strlen($new_word)) === $new_word) {
            if (search($array, $word, $new_word)) {
                return true;
            }
        }
    }
 
    return false;
}
 
$symbols = array('p', 'pa', 'aw');
var_dump(search($symbols, 'paw')); // true
var_dump(search($symbols, 'ppppawpa')); // true
var_dump(search($symbols, 'ppawap')); // false
 

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