<?php
error_reporting(-1);
$String = 'isNumeric(right(trim(contract_id),1))';

$func      = '\w+';
$const     = '[\w*&^+-]+';
$wspconst  = '[\w*&^+\s-]+';

$GetRx = '\s*((?:\s*('.$func.')\s*[(](?:(?>(?:(?!\s*'.$func.'\s*[(]|[)]).)+)|(?1))*[)]))';
$ParseRx = '((?:\s*('.$func.')\s*[(]((?: (?>(?:(?!\s*'.$func.'\s*[(]|[)]).)+)|(?1))*)[)]|\s*["\']('.$wspconst.')["\']\s*|\s*('.$const.')\s*|(?<=,)|(?<=^)(?!\s*$)))';

preg_match_all('/'.$GetRx.'/', $String, $Out, PREG_SET_ORDER);

foreach($Out as $Str){
    print "------------------\nParsing:\n$1\n\n";
    $res = parse_func($Str[1]);

    print "String to be eval()'ed:\n\n\n";
    break;
}

echo $res;

function parse_func($core=''){
    GLOBAL $ParseRx;
    $core = preg_replace_callback('/'.$ParseRx.'/', 'parse_callback', $core);
    return $core;
}

function parse_callback($matches){
    $fname = (isset($matches[2]) ? $matches[2] : '');
    $fbody = (isset($matches[3]) ? $matches[3] : '');
    $fconst = (isset($matches[4]) ? $matches[4].(isset($matches[5]) ? $matches[5] : '') : '');
    if ($fbody != ''){
        return "{'$fname'=>[" . (parse_func( $fbody )) . "]}";
    }
    return "'$fconst'";
}
?>