php 5.4 - skin deep syntactic sugar

I was quite excited to see that php 5.4 was getting some sugar for array definitions. e.g. "array(1,2,3)" would finally become "[1,2,3]". I was also excited to see "array dereferencing" was fixed or accessing an array by index after it is returned from a function e.g. "func()[index]". However let us be clear in noting that this does NOT mean it has attained the flexibility one would anticipate. For instance you can not immediately access an array after declaring it such as "['name' => 'peter', 'age' => 30]['age']" results in a syntax error. Of course you could combine both of the new features to do "func(['name' => 'peter', 'age' => 03])['age']" - which probably covers the majority of ways in which it would be used. The other issue I have is the inability to access a function upon it's return from function application e.g. "func(1)(2)" will result in a syntax error. This is problematic for higher order techniques that benefit dynamic languages.

Why would anyone want features such as those I have outlined above? People designing "in language" domain specific languages benefit greatly from such flexibility. Particularly in a language which already limits facilities for creating such mythical beasts.

That being said - I will gladly let go of my personal hack for passing in name/value pairs to a function which I have lovingly/jokingly referred to as "appositive expressions" e.g. "func('key', 'value', 'key2', 'value2')" can now become "func(['key' => 'value', 'key2' => 'value2'])". It is not surprising at all that php finally gets this feature as ruby finally bit the bullet and now accepts the json esque ":" in place of the "hash rocket =>". '

I should mention that the addition of "traits" will go miles in cleaning up some otherwise convoluted approaches to attaining mixins in php! I am very excited to see how this is utilized by the different frameworks.

Keyword Functions in PHP

So, as spurned by a comment on hacker news relating to the lack of ability for keyword arguments in php I figured I would expound more upon the Phutility library, in particular the Func module.

Check it out:

#say you have a function (perhaps defined by you, perhaps not)

namespace SomeNamespace;
use Phutility\Func; 

function testFunc($name, $eyes, $hair = 'blonde', $age = 0, $weight = 200, $goatFace = 'definitely') {
    return array(
        'name' => $name, 
        'eyes' => $eyes, 
        'hair' => $hair, 
        'age' => $age, 
        'weight' => $weight,
        'goatFace' => $goatFace);
}

#if you want a keyword wrapper for it:

$testFuncWrapper = Func::keyword('\SomeNamespace\testFunc'); 

$result = $testFuncWrapper(
    age, 30,
    name, 'peter'
);

/*would yield a $result of
array(
    'name' => 'peter',
    'eyes' => 'blue',
    'hair' => 'blonde',
    'age' => 30,
    'weight' => 1200,
    'goatFace' => 'definitely'
)
*/

# If you want to not have a variable func you would need to do something like:
function TestFuncWrapper() {
    static $wrapper; 
    if(!$wrapper) {
        $wrapper = Func::keyword('\SomeNamespace\TestFunc');
    }

    return call_user_func_array($wrapper, func_get_args());
}

#a little gnarlier but this is the price we pay to call it like:

$result = TestFuncWrapper(
    goatFace, 'NoWay'
);

#oops this would yield an exception because name and age are required!

If this is at all interesting to you and you'd like to use it or contribute, the source and tests are all up on github.

On Phutility

Phutility is a collection of tools which I utilize in many of my other projects. For example the Node class is utilized by both covenants (sql builder) and also phmop (meta object protocol). Today though I am going to be discussing some of the work that I have been doing in Func to lay the framework for "higher order object oriented programming" with phmop. To give you an idea of what I am driving at, consider:

defineClass('Person', 
    slot('someMethod', function($self) {
        $args = func_get_args();
        $self = array_shift($args);
        $options = appos($args);
        if($self->{$options[ifField]} == $options[isValue]) {
            $self->call($options[callMethod], $options[withValues]);
        }
    })->accessor('someMethod'));

$person = new Person;
$person->someMethod(
    ifField, 'age',
    isValue, 30, 
    callMethod, 'someMethod2', 
    withValues, array(300));

There are a few things we can cleanup. Firstly lets create a function "method" which wraps up simple functions which utilize an accessor which is the same as their internal name. Then lets utilize a higher order function "Func\options" which returns a function which has the last param defined as an options hash to clean things up:

defineClass('Person', 
    method('someMethod', Func\options(function($self, $options) {
        if($self->{$options[ifField]} == $options[isValue]) {
            $self->call($options[callMethod], $options[withValues]);}})));

But we can go further by creation an optionsMethod which wraps up the need for the explicit Func\options call. Also we can have it pass a param which gives us back a std class for options rather than an array.

defineClass('Person', 
    optionsMethod('someMethod', function($self, $options) {
        if($self->{$options->ifField} == $options->isValue) {
            $self->call($options->callMethod, $options->withValues);}}));

For the sake of completeness let me show off another way this could be defined more explicitly taking advantage of Func\keyword which evaluates a closure and then returns a function which responds to an appositive style call:

$keywordFunc = Func\keyword(function($age, $name, $color) {
    return array('age' => $age, 'name' => $name, 'color' => $color);
});

print_r($keywordFunc(
    age, 30, 
    color, 'blue', 
    name, 'peter'));

array(
    'age' => 30,
    'name' => 'peter',
    'color' => 'blue');

As you can see this allows us to pass the params in any order we please (which to be fair our Func\options implementation does as well but packaged into an $options var). So now we will skip to step 3 of what a keywordMethod would look like in use:

defineClass('Person', 
    keywordMethod('someMethod', 
        function($self, $ifField, $isValue, $callMethod, $withValues) {
            if($self->$ifField == $isValue) {
                $self->call($callMethod, $withValues);}}));

$person = new Person;
$person->someMethod(
    ifField, 'age',
    isValue, 30, 
    callMethod, 'someMethod2', 
    withValues, array(300));

I think this makes clear why both a meta object protocol and higher order functions are so awesome when they can play together. Rather than having only inheritence, interfaces, or even mixins, as the tool for making things more elegant we can easily add new features to our language with simple function composition.

Considering a MetaObject Protocol for PHP

The purpose of a "MetaObject Protocol" is to allow for defining the very nature of how an object system functions. This means the ability to add traits/mixins, aspects, multiple inheritance, "Generics" etc. w/o requiring compilation or low level tinkering. One major advantage is that this means not having to wait for a revision of your language to express certain design patterns.

As usual php is so close, yet so far away. However ab/utiliz/ing the magic methods you can actually get pretty close to something resembling the CLOS system. To accomplish this it requires a few building blocks which I have abstracted into my Phutility library. Primarily the MetaArg and Node which provide the building blocks for composing declarative domain specific languages.

The majority of the magic occurs via macro expansion in CLOS. We are going to make up for that via declaring an abstract syntax tree (AST) which we will expand and weave into our method dispatch mechanism.

Enough talk, let's code. First our goal is be able to declare classes and methods.

defineClass('Shape',
    slot('width'),
    slot('height'),
    method('getHeight', function($self) {
        return $self->height;
    }), 
    method('getArea', function($self) {
        return $self->width * $self->height;
    })
);

$shape = new Shape(
    width, 20, 
    height, 50
);

echo $shape->getHeight();
echo $shape->getArea();

defineGeneric('beforeGetArea', 
    before(getArea),
    arity(Shape), 
    function($self) {
        echo "Called before get area!\n";
    }
);

echo $shape->getArea(); //outputs "Called before get area!" and then area

Looks like a class and acts like a class. But most definitely not a raw class. How does this work? Principally we keep the meta information about each class in a Registry. Each class defined results in a simple declaration of "class X extends \phmop\StandardClass{}" which allows the usual "new Class" syntax. It writes this to a cache directory and does a require_once on it so as to avoid eval.

The base Obj class looks something like:

class StandardClass {
    public $slots = array();

    public function __call($slot, $args) {
        return Registry::dispatchMethod($this, $slot, $args);
    }

    public function &__get($slot) {
        return Registry::getSlot($this, $slot);
    }

    public function __set($slot, $value) {
        Registry::setSlot($this, $slot, $value);
    }

    public function __construct() {
        foreach(Appos(func_get_args()) as $key => $val) { 
            $this->$key = $val;
        }
    }
}

So pretty clearly the real magic is taking place in the way that defineClass, defineGeneric, and friends interoperate with the Registry.

I am going to end things here for now as I need to make a few posts about some of the inner workings of phutility to really get into the thick of things.

Revision to php TCO trampoline

github.com/shaunxcode/php-trampoline

Sometimes I wake up at 6am with the frightful knowledge that there is an edge case to something I wrote somewhere which is incorrect. The only thing worse than knowing someone on the internet is wrong (http://xkcd.com/386/) is knowing you were wrong on the internet.

I realized in a dream that my trampoline would not work with higher order functions as it currently stands because the while loop is based on is_callable, obviously if your function is meant to return a function you would not want it to be executed immediately (particularly because it probably expects arguments etc.). All of a sudden the whole throwing an exception approach made sense - however thanks to php5.3s __invoke method I can handle this cleanly by wrapping each tail call in an instance of TrampolineBounce and then check "$return instanceof TrampolineBounce".

I figured if I am going to need a Trampoline class I may as well leverage __callStatic to allow for easier invocation of trampolined functions. With out further ado:

namespace Trampoline;

class Bounce {
        private $func;
        public function __construct($func) {
                $this->func = $func;
        }

        function __invoke() {
                return call_user_func_array($this->func, array());
        }
}

class Trampoline {
        public static function Bounce($func) {
                return new Bounce($func);
        }

        public static function __callStatic($func, $args) {
                $return = call_user_func_array($func, $args);
                while($return instanceof Bounce) {
                        $return = $return();
                }

                return $return;
        }
}

function even($n) {
        return $n == 0 ? true : Trampoline::Bounce(function() use($n) { return odd($n - 1);});
}

function odd($n) {
        return $n == 0 ? false : Trampoline::Bounce(function() use($n) { return even($n - 1);});
}


echo Trampoline::even(1500) ? 'Yep' : 'Nope';

tail call optimization in php 5.3

*note this has been revised: (http://commonphp.blogspot.com/2010/12/revision-to-php-tco-trampoline.html) *

So I have been holding off on releasing my php lisp for the past couple of months for a few reasons. The first was I wanted to get quasiquotes/macros working correctly and the other was I wanted to get TCO working correctly. I checked quasiquotation and macro expansion off a few weeks ago and have been wrestling with TCO since. There are many work arounds such as only using higher order functions like map etc. which "underneath" use php foreach/while etc. but this always felt like a hack. Today I will show how I am accomplishing TCO. It is actually "pretty" enough that I would even use this technique in "normal" php if the need arose i.e. when implementing an algorithm where mutual recursion is the cleanest way of dealing with a given problem.

I had heard "tail" of a magical device called a "trampoline" but had yet to see one implemented in php. First lets set the scene for why such a thing is necessary.

Regular mutually recursive functions:

function even($n) { 
    return $n == 0 ? true : odd($n - 1);
}

function odd($n) { 
    return $n == 0 ? false: even($n - 1);
}

echo even(15000000) ? 'Yep' : 'Nope'; 

Result?
Fatal error: Allowed memory size of 335544320 bytes exhausted (tried to allocate 261900 bytes)

As you can imagine this would blow the stack pretty quickly. The solution is to return closures which close over the next function to be executed by the trampoline:

function trampoline($func, $args) { 
    $return = call_user_func_array($func, $args);
    while(is_callable($return)) {
        $return = $return();
    }
    return $return;
}

Ready for trampoline version of functions, notice the closures being returned:

function even($n) { 
    return $n == 0 ? true : function() use($n) { return odd($n - 1); };
}

function odd($n) { 
    return $n == 0 ? false : function() use($n) { return even($n - 1); };
}

echo trampoline('even', array(15000000)) ? 'Yep' : 'Nope';

No more blowing the stack!

For another example here's a tail call version of factorial:

function fact($n) {
    $product = function($min, $max) use($n, &$product) { 
    return $min == $n ? 
        $max : 
        function() use(&$product, $min, $max) {
            return $product(bcadd($min, 1), bcmul($min, $max));
        };
    };
    return $product(1, $n);
}

echo trampoline('fact', array(5050));

Result?
48424893876442346868149955534231630311152316586879831768663469768542209496025625521335165836597244986775871359731653944863304801472363186993340977071916545094098397335673370033050095301846673812319519184368943848940208083286841710046697935471447379350531958006231636490517114754236601801475241025829782559539886360417931118962453657701734674670226076209971728976092053885317753609072349073735823517244188123450674446015646408575152721563438720528695200000950089076496921144117143216432888312645825602479454709341393797835166357888263581672355452853869124012486552503932416596193377435247315025743200744002301394585228500268455104719958806656594340592125681513366273489623936710098205543483870278942617415439360839831622538877203695372405175195820803498878614463408507559071691975942963055323977023975579962356660525443011519924497192606177308403911494610046020125224506026847906849303464211582255596044461695809931170735992902861015153948973924760246045409447614027579732580231716105662183345892311470363765765619375852044952237375592745997667408717094345683918382540158972633294341661753292428842087402347931146455707829443369742629955406096433554614672210416043568566713315721328986242009438119615170550083892805000693555351590233960368408610557369747063249171375287938142229602269575258888078115537273321885243640816116313033760859934727694805934472650247398590268106132632051710011975357435411073973400518009267243861234604382480972044372345571394804592046625365990943593155118312928026092849203020843936635478814979107242813498013904401479307173527813374488927846868388843629960975688405420793866362748625568963809336537735196635482323869611480442317616213118017936592673957745954854119905353862738630397953491904711075413351939493239103430359228666385849114266162025489907918597974910444817388693635468572983832473160429177887474388606642754513228627277514269543214565586593047881932646980529181738704933529003783674019143726269073240250043051103116046759758599556492457493255007087656022414606222859948126380313826837273496022239059049197478197470692778763575742323649675518937743998020384086092356484327490394949151360442183700474945898304321062066355143800014715430781407860862440970162255814321544952627961522489938257459652704978558232366966762259286202122152536234765500508950380085381022529769410646695981455932497274422145956223070614311782386939393660505071468075609946312266961804079078124972138751570252042991908322662337184841517195535818561858155408260788044667462475133702274158651640293943156955741104099223849587202623924618562507307459878359309762592535803298228381823574279830281362305301068394370171580376856819398786773168976316243886413852653396055497826310062540076987247412010421678922894559582379982459315131410353844686814801084428315428961052501286596189198414322404856396902069457672137306587727429077418184644185029820725981473585275798688633870939149445242039540994144936753560145261967645980942905198036844963065770953567278843744815101688364553167567561127581285151504170857163788476814410430818485342212602471021116122232536945437600193563274350613219002205135771961855617387540043201574995936521078443417355808962389471634447182986942493573328833479027327904592963332830948909056606878114712587614797355021919494836468834407159424831076501904939674180550971070685974826026825572462514492992573071756584471446779582538562871889253777491503761958039422843336111308820256625552392100765429247159402181090198939792727134760027285582388085697688779314720476653237742989447851866203189262136310101262960823946227816914290542573075004229606139191853412465867836753036378462157616915664130017838805074756547841197620513628237540972492294319305705734478032962949128924196666202655682340324787692515590130551301935088659828410687356942341790891345277677382788831208787364801395111486357308798265828146035781558094135067110230536901270297547242166950881473214274739101845553727897045531119954725288893493225046788944932736466460550726919323972814208640861318915500012832311138673106892856437774916302054198800992266101283582978474791023088963610289841529824634218025633260218581419143652195694797922926870213605428040752771533690783079334348985159752481190866305108822791928707079718613729022578623134006395058165941963834815415900225540158365512962747234118295298072392721688699472738462833608355509413369430747483292086244416854740060940250464784905488189338770945263660330117646978971876652613557429461658723058825915031208985735140615497693407650641375234834094995218262573623896322220855235269130698919365626682758374382064483940359436309642974808514506879129036989811006578121058886468214783989745311306991381502598738427646690529026148074559926029141700545754931041231062108024348298640252182862477489626497023992723452959298403206063199087668949604632790351230972033067574210447769545912131839504735995523543564698434762288745349217285435045940022877153117114056361355516568793184887831573689961226955484323093901470710251285589637162339096014594590326637778408537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So in other words PHLISP should be officially released by christmas eve.

PHP to javascript fluent expressions

There are many times in Voltron views where I need to make a jquery/javascript call, initially I compromised and created the UI::ScriptSnippet in which I would put the typical "$(document).ready(function(){})" type deal in place. This was becoming increasingly more obnoxious particularly when the rest of the view code was so clean. So I give you the JSCallBuilder:

    UI::JSCall('object')->method(array('a' => 'b')); 
    // renders to object.method({'a': 'b'}); 

    UI::JSReady('object')->method(array('a' => 'b')); 
    //renders to <\script type="text/javascript">$(document).ready(function(){ object.method({'a', 'b'}) });<\/script> 
*/note the escaped script tags for bloggers sake? */

The source to make this happens is relatively trivial: http://code.google.com/p/phpviewadapter/source/browse/trunk/UI/JSCallBuilder.php

solving the word cube in voltron

In response to: http://programmingpraxis.com/2010/07/13/word-cube/

/* returns array of words found in the 9 letters provided */
function solveCube($letters) {
    $words = newType(TFile, 'words.txt')->splitBy("\n");

    return newType(TString, $letters)
        ->asArray
        ->powerSet('contains', $letters[4])
        ->map('permutations', I('asString')->in($words))
        ->map('join');
}

echo solveCube('ncbciune');

There are a few alternative ways that could be written and I am not sure if the idea of just having an optional filter as arguments to powerSet and permutations is entirely intuitive but the reality is that w/o the filter permutations will die on anything over 8 unless you crank the memory up in php.ini and thats just filthy.

Next post I will delve into iterative permutation and powerset internals on Array as that is obviously where the meat of that solution lies.