one can now register handler classes through particles.

src/Pho/Framework/Handlers/Form.php

@@ -34,16 +34,31 @@ public static function handle(
         array $args
         ):  \Pho\Lib\Graph\EntityInterface
     {    
-        $class = self::findFormativeClass($name, $args, $pack);
+        $class = static::findFormativeClass($name, $args, $pack);
+        $head = static::formHead($particle, $args);
+        $edge_class = $pack["out"]->formative_label_class_pairs[$name];
+        $edge = new $edge_class($particle, $head);
+        return $edge->return();
+    }
+
+    /**
+     * Forms the head particle.
+     *
+     * @param ParticleInterface $particle
+     * @param array $args
+     * 
+     * @return void
+     */
+    protected static function formHead(
+        ParticleInterface $particle, 
+        array $args): void
+    {
         if(count($args)>0) {
             $head = new $class($particle, $particle->where(), ...$args);
         }
         else {
             $head = new $class($particle, $particle->where());
         }
-        $edge_class = $pack["out"]->formative_label_class_pairs[$name];
-        $edge = new $edge_class($particle, $head);
-        return $edge->return();
     }
 
     /**

src/Pho/Framework/Handlers/Gateway.php

@@ -12,6 +12,7 @@
 namespace Pho\Framework\Handlers;
 
 use Pho\Framework\ParticleInterface;
+use Pho\Framework\Exceptions\InvalidParticleMethodException;
 
 /**
  * Handler Gateway
@@ -24,6 +25,18 @@
 class Gateway
 {
 
+    /**
+     * Default Handler adapters
+     *
+     * @var array
+     */
+    protected $adapters = [
+        "form" => __NAMESPACE__ . "\\Form::handle", 
+        "get"  => __NAMESPACE__ . "\\Get::handle", 
+        "has"  => __NAMESPACE__ . "\\Has::handle",
+        "set"  => __NAMESPACE__ . "\\Set::handle"
+    ];
+
     /**
      * The particle that this handler is associated with.
      *
@@ -61,6 +74,21 @@ public function __construct(ParticleInterface $particle) {
         $this->particle = $particle;
     }
 
+    /**
+     * Registers a new handler adapter.
+     *
+     * Default handlers may be overriden.
+     * 
+     * @param string $key Adapter key; e.g. "get", "set", "form" etc.
+     * @param string $class Handler class to register. A handler class shall implement HandlerInterface
+     * 
+     * @return void
+     */
+    public function registerHandlerAdapter(string $key, string $class): void
+    {
+        $this->adapters[$key] = $class;
+    }
+
     /**
      * Packs cargo variables
      *
@@ -91,27 +119,28 @@ protected function pack(): array
      */
     public function switch(string $name, array $args) /*:  \Pho\Lib\Graph\EntityInterface*/
     {
+        $deliver = function(string $key) use ($name, $args) {
+            $class = $this->adapters[$key];
+            return $class($this->particle, $this->pack(), $name, $args);
+        };
+
         if(in_array($name, $this->cargo_out->setter_labels)) {
-            return Set::handle($this->particle, $this->pack(), $name, $args);
+            return $deliver("set");
         }
         else if(in_array($name, $this->cargo_out->formative_labels)) {
-            return Form::handle($this->particle, $this->pack(), $name, $args);
+            return $deliver("form");
         }
         else if(strlen($name) > 3) {
             $func_prefix = substr($name, 0, 3);
-            $funcs = [
-                "get"=> __NAMESPACE__ . "\\Get::handle", 
-                "has"=> __NAMESPACE__ . "\\Has::handle",
-                "set"=> __NAMESPACE__ . "\\Set::handle",
-            ];
-            if (array_key_exists($func_prefix, $funcs) ) {
+            if (array_key_exists($func_prefix, $this->adapters) ) {
                 try {
-                    return $funcs[$func_prefix]($this->particle, $this->pack(), $name, $args);
+                    return $deliver($func_prefix);
                 }
-                catch(\Pho\Framework\Exceptions\InvalidParticleMethodException $e) {
+                catch(\Exception $e) {
                     throw $e;
                 }
             }
         }
+        throw new InvalidParticleMethodException(__CLASS__, $name);
     }
 }

src/Pho/Framework/Handlers/Get.php

@@ -47,14 +47,14 @@ public static function handle(
         ) /*:  array*/
     {
         $name = substr($name, 3);
-        if(self::methodExists($pack, $name, Direction::out())) {
-            return self::getEdgeNodes($particle, $pack, $name, Direction::out());
+        if(static::methodExists($pack, $name, Direction::out())) {
+            return static::getEdgeNodes($particle, $pack, $name, Direction::out());
         }   
-        elseif(self::methodExists($pack, $name, Direction::in())) {
-            return self::getEdgeNodes($particle, $pack, $name, Direction::in());
+        elseif(static::methodExists($pack, $name, Direction::in())) {
+            return static::getEdgeNodes($particle, $pack, $name, Direction::in());
         }
         elseif( FieldHelper::fieldExists($pack["fields"], $name) ) {
-            return self::getField($particle, $pack["fields"], $name, $args);
+            return static::getField($particle, $pack["fields"], $name, $args);
         }
         throw new \Pho\Framework\Exceptions\InvalidParticleMethodException(__CLASS__, $name);
     }
@@ -118,7 +118,7 @@ protected static function getEdgeNodes(
     {
         $name = strtolower($name);
         $direction = (string) $direction;
-        $node_adj = self::ADJACENCY_EQUIVALENT[$direction];
+        $node_adj = static::ADJACENCY_EQUIVALENT[$direction];
         $cargo = $pack[$direction];
         $edges = $particle->edges()->$direction();
         $return = [];

src/Pho/Framework/Handlers/Has.php

@@ -56,11 +56,11 @@ public static function handle(
         $name = strtolower(substr($name, 3));
 
 
-        if(self::methodExists($pack, $name, $id, Direction::out())) {
-            return self::checkEdgeNode($particle, $pack, $name, $id, Direction::out());
+        if(static::methodExists($pack, $name, $id, Direction::out())) {
+            return static::checkEdgeNode($particle, $pack, $name, $id, Direction::out());
         }   
-        elseif(self::methodExists($pack, $name, $id, Direction::in())) {
-            return self::checkEdgeNode($particle, $pack, $name, $id, Direction::in());
+        elseif(static::methodExists($pack, $name, $id, Direction::in())) {
+            return static::checkEdgeNode($particle, $pack, $name, $id, Direction::in());
         }
 
         throw new \Pho\Framework\InvalidParticleMethodException(__CLASS__, $original_name);
@@ -106,7 +106,7 @@ protected static function checkEdgeNode(
         ): bool
     {
         $direction = (string) $direction;
-        $node_adj = self::ADJACENCY_EQUIVALENT[$direction];
+        $node_adj = static::ADJACENCY_EQUIVALENT[$direction];
         $cargo = $pack[$direction];
         $edges = $particle->edges()->$direction();
         foreach($edges as $edge) {

src/Pho/Framework/Handlers/Set.php

@@ -37,7 +37,7 @@ public static function handle(
         ) /*:  \Pho\Lib\Graph\EntityInterface*/
     {
         if( FieldHelper::fieldExists($pack["fields"], substr($name, 3)) ) {
-            return self::field($particle, $pack["fields"], substr($name, 3), $args[0]);
+            return static::field($particle, $pack["fields"], substr($name, 3), $args[0]);
         }
         $check = false;
         foreach($pack["out"]->setter_label_settable_pairs[$name] as $settable) {
@@ -71,9 +71,9 @@ protected static function field(
     {
         $name = FieldHelper::findFieldName($cargo, $name);
         if(isset($cargo->fields[$name]["constraints"])) {
-                self::probeField($cargo->fields[$name]["constraints"], $value);
+                static::probeField($cargo->fields[$name]["constraints"], $value);
         }
-        $particle->attributes()->$name = self::applyDirectives($value, $cargo->fields[$name]);
+        $particle->attributes()->$name = static::applyDirectives($value, $cargo->fields[$name]);
     }
 
     /**

src/Pho/Framework/ParticleTrait.php

@@ -139,6 +139,21 @@ public function registerOutgoingEdgeClass(string $class): void
         );
     }
 
+    /**
+     * Registers a new handler adapter.
+     *
+     * Default handlers may be overriden.
+     * 
+     * @param string $key Adapter key; e.g. "get", "set", "form" etc.
+     * @param string $class Handler class to register. A handler class shall implement HandlerInterface
+     * 
+     * @return void
+     */
+    public function registerHandlerAdapter(string $key, string $class): void
+    {
+        $this->handler->adapters[$key] = $class;
+    }
+
     /**
      * @internal
      *