pipetest.php

<?php

function getAttributesFromTheme(string $themeName)
{
    $theme = $this->getTheme($themeName);
    if (empty($theme)) {
        return null;
    }
    $xml = $this->getXmlFromTheme($theme);
    if (empty($xml)) {
        return null;
    }
    return $this->extractAttributes($xml);
}

function caller()
{
    $attributes = $this->getAttributesFromTheme('mytheme');
}

function getAttributesFromTheme(string $themeName)
{
    return Pipe::make(
        $this->getTheme(...),
        $this->getXmlFromTheme(...),
        $this->extractAttributes(...)
    )
    ->stopIfEmpty()
    ->from($themeName);
}

function caller()
{
    $attributes = $this->getAttributesFromTheme('mytheme')->run();
}