function compose example ... see http://qiita.com/yuya_takeyama/items/b65afa141327e7ccd1ac

01.php

<?php
function compose(callable $initial, callable ...$functions)
{
    if (count($functions) < 1) {
        throw new \InvalidArgumentException('at least two functions are required');
    }

    return array_reduce($functions, function ($f, $g) {
        return function (...$args) use ($f, $g) {
            return $f($g(...$args));
        };
    }, $initial);
}

$splitAsWords = function ($str) {
    return \preg_split('/\s+/u', $str);
};
$camelizeWords = function ($words) {
    return \array_map('ucfirst', $words);
};
$join = function ($words) {
    return \join('', $words);
};
$lowerCamelize = compose('lcfirst', $join, $camelizeWords, $splitAsWords);

echo $lowerCamelize('foo bar baz'); // => "fooBarBaz"

02.php

<?php
function compose(callable ...$functions)
{
    if (count($functions) < 2) {
        throw new \InvalidArgumentException('at least two functions are required');
    }

    return array_reduce($functions, function ($f, $g) {
        return $f ? function (...$args) use ($f, $g) {
            return $f($g(...$args));
        }: $g;
    });
}

$splitAsWords = function ($str) {
    return \preg_split('/\s+/u', $str);
};
$camelizeWords = function ($words) {
    return \array_map('ucfirst', $words);
};
$join = function ($words) {
    return \join('', $words);
};
$lowerCamelize = compose('lcfirst', $join, $camelizeWords, $splitAsWords);

echo $lowerCamelize('foo bar baz'); // => "fooBarBaz"

03.php

<?php
function compose(callable ...$functions)
{
    if (count($functions) < 2) {
        throw new \InvalidArgumentException('at least two functions are required');
    }

    return array_reduce($functions, function ($f, $g) {
        return function (...$args) use ($f, $g) {
            return $f ? $f($g(...$args)) : $g(...$args);
        };
    });
}

$splitAsWords = function ($str) {
    return \preg_split('/\s+/u', $str);
};
$camelizeWords = function ($words) {
    return \array_map('ucfirst', $words);
};
$join = function ($words) {
    return \join('', $words);
};
$lowerCamelize = compose('lcfirst', $join, $camelizeWords, $splitAsWords);

echo $lowerCamelize('foo bar baz'); // => "fooBarBaz"

04.php

<?php
function compose(callable ...$functions)
{
    if (count($functions) < 2) {
        throw new \InvalidArgumentException('at least two functions are required');
    }

    return array_reduce($functions, function ($f, $g) {
        return function (...$args) use ($f, $g) {
            return $f($g(...$args));
        };
    }, function ($v) { return $v; });
}

$splitAsWords = function ($str) {
    return \preg_split('/\s+/u', $str);
};
$camelizeWords = function ($words) {
    return \array_map('ucfirst', $words);
};
$join = function ($words) {
    return \join('', $words);
};
$lowerCamelize = compose('lcfirst', $join, $camelizeWords, $splitAsWords);

echo $lowerCamelize('foo bar baz'); // => "fooBarBaz"