diff --git a/src/Composer2Nix/ComposerConfig.php b/src/Composer2Nix/ComposerConfig.php
new file mode 100644
index 0000000..a134835
--- /dev/null
+++ b/src/Composer2Nix/ComposerConfig.php
@@ -0,0 +1,67 @@
+<?php
+namespace Composer2Nix;
+use Exception;
+
+class ComposerConfig
+{
+	public $packageName;
+
+	public $packages;
+
+	public $devPackages;
+
+	public $values;
+
+	public function __construct($configFile, $lockFile, $packageName, $noDev)
+	{
+		/* Open the composer.json file and decode it */
+		$composerJSONStr = file_get_contents($configFile);
+
+		if($composerJSONStr === false)
+			throw new Exception("Cannot open contents of: ".$configFile);
+
+		$this->values = json_decode($composerJSONStr, true);
+
+		/* If no package name has been provided, attempt to use the name in the composer config file */
+		if($packageName === null)
+		{
+			if(array_key_exists("name", $this->values))
+				$packageName = $this->values["name"];
+			else
+			{
+				throw new Exception("Cannot determine a package name! Either add a name\n".
+					"property to the composer.json file or provide a --name parameter!");
+			}
+		}
+
+		$this->packageName = strtr($packageName, "/", "-"); // replace / by - since / is not allowed in Nix package names
+
+		/* Open the lock file and decode it */
+
+		if(file_exists($lockFile))
+		{
+			$composerLockStr = file_get_contents($lockFile);
+
+			if($composerLockStr === false)
+				throw new Exception("Cannot open contents of: ".$lockFile);
+
+			$lockConfig = json_decode($composerLockStr, true);
+			
+			if(array_key_exists("packages", $lockConfig))
+				$this->packages = $lockConfig["packages"];
+			else
+				$this->packages = array();
+
+			if(!$noDev && array_key_exists("packages-dev", $lockConfig))
+				$this->devPackages = $lockConfig["packages-dev"];
+			else
+				$this->devPackages = array();
+		}
+		else
+		{
+			$this->packages = array();
+			$this->devPackages = array();
+		}
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/Dependency.php b/src/Composer2Nix/Dependencies/Dependency.php
new file mode 100644
index 0000000..a8b4f51
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/Dependency.php
@@ -0,0 +1,73 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use Composer2Nix\NixASTNode;
+use Exception;
+
+abstract class Dependency extends NixASTNode
+{
+	public $package;
+
+	protected $sourceObj;
+
+	protected function __construct(array $package, array $sourceObj)
+	{
+		$this->package = $package;
+		$this->sourceObj = $sourceObj;
+	}
+
+	private static function selectSourceObject($preferredInstall, array $package)
+	{
+		if($preferredInstall === "source")
+		{
+			if(array_key_exists("source", $package))
+				return $package["source"];
+			else if(array_key_exists("dist", $package))
+				return $package["dist"];
+			else
+				throw new Exception("Encountered a dangling package reference");
+		}
+		else
+		{
+			if(array_key_exists("dist", $package))
+				return $package["dist"];
+			else if(array_key_exists("source", $package))
+				return $package["source"];
+			else
+				throw new Exception("Encountered a dangling package reference");
+		}
+	}
+
+	public static function constructDependency(array $package, $preferredInstall)
+	{
+		$sourceObj = Dependency::selectSourceObject($preferredInstall, $package);
+
+		switch($sourceObj["type"])
+		{
+			case "path":
+				return new PathDependency($package, $sourceObj);
+			case "zip":
+				return new ZipDependency($package, $sourceObj);
+			case "git":
+				return new GitDependency($package, $sourceObj);
+			case "hg":
+				return new HgDependency($package, $sourceObj);
+			case "svn":
+				return new SVNDependency($package, $sourceObj);
+			default:
+				throw new Exception("Cannot convert dependency of type: ".$sourceObj["type"]);
+		}
+	}
+
+	public function toNixAST()
+	{
+		$dependency = array();
+
+		if(array_key_exists("target-dir", $this->package))
+			$dependency["targetDir"] = $this->package["target-dir"];
+		else
+			$dependency["targetDir"] = "";
+
+		return $dependency;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/GitDependency.php b/src/Composer2Nix/Dependencies/GitDependency.php
new file mode 100644
index 0000000..1972d3d
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/GitDependency.php
@@ -0,0 +1,38 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunInvocation;
+
+class GitDependency extends Dependency
+{
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	public function toNixAST()
+	{
+		$dependency = parent::toNixAST();
+
+		$outputStr = shell_exec('nix-prefetch-git "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
+
+		if($outputStr === false)
+			throw new Exception("Error while invoking nix-prefetch-git");
+		else
+		{
+			$output = json_decode($outputStr, true);
+			$hash = $output["sha256"];
+
+			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchgit"), array(
+				"name" => strtr($this->package["name"], "/", "-").'-'.$this->sourceObj["reference"],
+				"url" => $this->sourceObj["url"],
+				"rev" => $this->sourceObj["reference"],
+				"sha256" => $hash
+			));
+		}
+
+		return $dependency;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/HgDependency.php b/src/Composer2Nix/Dependencies/HgDependency.php
new file mode 100644
index 0000000..d4e4a1c
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/HgDependency.php
@@ -0,0 +1,35 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunInvocation;
+
+class HgDependency extends Dependency
+{
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	public function toNixAST()
+	{
+		$dependency = parent::toNixAST();
+
+		$hash = shell_exec('nix-prefetch-hg "'.$this->sourceObj['url'].'" '.$this->sourceObj["reference"]);
+		
+		if($hash === false)
+			throw new Exception("Error while invoking nix-prefetch-hg");
+		else
+		{
+			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchhg"), array(
+				"name" => strtr($package["name"], "/", "-").'-'.$this->sourceObj["reference"],
+				"url" => $this->sourceObj["url"],
+				"rev" => $this->sourceObj["reference"],
+				"sha256" => $hash
+			));
+		}
+
+		return $dependency;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/PathDependency.php b/src/Composer2Nix/Dependencies/PathDependency.php
new file mode 100644
index 0000000..e945438
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/PathDependency.php
@@ -0,0 +1,20 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use PNDP\NixGenerator;
+use PNDP\AST\NixFile;
+
+class PathDependency extends Dependency
+{
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	public function toNixAST()
+	{
+		$dependency = parent::toNixAST();
+		$dependency["src"] = new NixFile($sourceObj['url']);
+		return $dependency;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/SVNDependency.php b/src/Composer2Nix/Dependencies/SVNDependency.php
new file mode 100644
index 0000000..7f7628e
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/SVNDependency.php
@@ -0,0 +1,35 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunInvocation;
+
+class SVNDependency extends Dependency
+{
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	public function toNixAST()
+	{
+		$dependency = parent::toNixAST();
+
+		$hash = shell_exec('nix-prefetch-svn "'.$sourceObj['url'].'" '.$sourceObj["reference"]);
+
+		if($hash === false)
+			throw new Exception("Error while invoking nix-prefetch-svn");
+		else
+		{
+			$dependency["src"] = new NixFunInvocation(new NixExpression("fetchsvn"), array(
+				"name" => strtr($package["name"], "/", "-").'-'.$sourceObj["reference"],
+				"url" => $sourceObj["url"],
+				"rev" => $sourceObj["reference"],
+				"sha256" => $hash
+			));
+		}
+
+		return $dependency;
+	}
+}
+?>
diff --git a/src/Composer2Nix/Dependencies/ZipDependency.php b/src/Composer2Nix/Dependencies/ZipDependency.php
new file mode 100644
index 0000000..1a6405b
--- /dev/null
+++ b/src/Composer2Nix/Dependencies/ZipDependency.php
@@ -0,0 +1,55 @@
+<?php
+namespace Composer2Nix\Dependencies;
+use PNDP\NixGenerator;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFile;
+use PNDP\AST\NixFunInvocation;
+use PNDP\AST\NixURL;
+
+class ZipDependency extends Dependency
+{
+	public function __construct(array $package, array $sourceObj)
+	{
+		parent::__construct($package, $sourceObj);
+	}
+
+	public function toNixAST()
+	{
+		$dependency = parent::toNixAST();
+
+		if($this->sourceObj["reference"] == "")
+			$reference = "";
+		else
+			$reference = "-".$this->sourceObj["reference"];
+
+		if(substr($this->sourceObj["url"], 0, 7) === "http://" || substr($this->sourceObj["url"], 0, 8) === "https://")
+		{
+			$hash = shell_exec('nix-prefetch-url "'.$this->sourceObj['url'].'"');
+
+			if($hash === null)
+				throw new Exception("Error while invoking nix-prefetch-url");
+			else
+			{
+				$src = new NixFunInvocation(new NixFile("fetchurl"), array(
+					"url" => new NixURL($this->sourceObj["url"]),
+					"sha256" => substr($hash, 0, -1)
+				));
+			}
+		}
+		else
+			$src = new NixFile($this->sourceObj['url']);
+
+		$dependency["src"] = new NixFunInvocation(new NixExpression("composerEnv.buildZipPackage"), array(
+			"name" => strtr($this->package["name"], "/", "-").$reference,
+			"src" => $src
+		));
+
+		return $dependency;
+	}
+
+	public function toNixExpr($indentLevel, $format)
+	{
+		return NixGenerator::phpToIndentedNix($this->toNixAST(), $indentLevel, $format);
+	}
+}
+?>
diff --git a/src/Composer2Nix/Expressions/CompositionExpression.php b/src/Composer2Nix/Expressions/CompositionExpression.php
new file mode 100644
index 0000000..f7e1e71
--- /dev/null
+++ b/src/Composer2Nix/Expressions/CompositionExpression.php
@@ -0,0 +1,57 @@
+<?php
+namespace Composer2Nix\Expressions;
+use PNDP\NixGenerator;
+use PNDP\AST\NixAttrReference;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFunction;
+use PNDP\AST\NixFunInvocation;
+use PNDP\AST\NixFile;
+use PNDP\AST\NixImport;
+use PNDP\AST\NixInherit;
+use PNDP\AST\NixLet;
+use PNDP\AST\NixObject;
+use Composer2Nix\NixASTNode;
+
+class CompositionExpression extends NixASTNode
+{
+	public function __construct($outputFile, $composerEnvFile)
+	{
+		$this->outputFile = $outputFile;
+		$this->composerEnvFile = $composerEnvFile;
+	}
+
+	private function prefixRelativePath($target)
+	{
+		if(substr($target, 0, 1) == "/" || substr($target, 0, 2) == "./" || substr($target, 0, 3) == "../")
+			return $target;
+		else
+			return "./".$target;
+	}
+
+	public function toNixAST()
+	{
+		return new NixFunction(array(
+			"pkgs" => new NixFunInvocation(new NixImport(new NixExpression("<nixpkgs>")), array(
+				"system" => new NixInherit()
+			)),
+			"system" => new NixAttrReference(new NixExpression("builtins"), new NixExpression("currentSystem")),
+			"noDev" => false
+		), new NixLet(array(
+			"composerEnv" => new NixFunInvocation(new NixImport(new NixFile($this->prefixRelativePath($this->composerEnvFile))), array(
+				"stdenv" => new NixInherit("pkgs"),
+				"writeTextFile" => new NixInherit("pkgs"),
+				"fetchurl" => new NixInherit("pkgs"),
+				"php" => new NixInherit("pkgs"),
+				"unzip" => new NixInherit("pkgs")
+			))
+		), new NixFunInvocation(new NixImport(new NixFile($this->prefixRelativePath($this->outputFile))), array(
+			"composerEnv" => new NixInherit(),
+			"noDev" => new NixInherit(),
+			"fetchurl" => new NixInherit("pkgs"),
+			"fetchgit" => new NixInherit("pkgs"),
+			"fetchhg" => new NixInherit("pkgs"),
+			"fetchsvn" => new NixInherit("pkgs")
+		))));
+	}
+}
+?>
diff --git a/src/Composer2Nix/Expressions/PackagesExpression.php b/src/Composer2Nix/Expressions/PackagesExpression.php
new file mode 100644
index 0000000..6c19185
--- /dev/null
+++ b/src/Composer2Nix/Expressions/PackagesExpression.php
@@ -0,0 +1,102 @@
+<?php
+namespace Composer2Nix\Expressions;
+use Composer2Nix\ComposerConfig;
+use Composer2Nix\Dependencies\Dependency;
+use PNDP\NixGenerator;
+use PNDP\AST\NixAttrSet;
+use PNDP\AST\NixExpression;
+use PNDP\AST\NixFile;
+use PNDP\AST\NixFunction;
+use PNDP\AST\NixFunInvocation;
+use PNDP\AST\NixInherit;
+use PNDP\AST\NixLet;
+use PNDP\AST\NixNoDefault;
+use PNDP\AST\NixObject;
+use PNDP\AST\NixURL;
+use Composer2Nix\NixASTNode;
+
+class PackagesExpression extends NixASTNode
+{
+	public $executable;
+
+	public $symlinkDependencies;
+
+	public $config;
+
+	public $preferredInstall;
+
+	public function __construct(ComposerConfig $config, $executable, $symlinkDependencies, $preferredInstall)
+	{
+		$this->executable = $executable;
+		$this->symlinkDependencies = $symlinkDependencies;
+		$this->config = $config;
+		$this->preferredInstall = $preferredInstall;
+	}
+
+	private function generateDependenciesExpr(array $packages)
+	{
+		$dependencies = array();
+
+		foreach($packages as $package)
+		{
+			$dependency = Dependency::constructDependency($package, $this->preferredInstall);
+			$dependencies[$package["name"]] = $dependency;
+		}
+
+		return new NixAttrSet($dependencies);
+	}
+
+	private function generatePackageMetaDataExpr()
+	{
+		$meta = array();
+
+		if(array_key_exists("homepage", $this->config->values))
+			$meta["homepage"] = new NixURL($this->config->values["homepage"]);
+
+		if(array_key_exists("license", $this->config->values))
+		{
+			if(is_string($this->config->values["license"])) // If the license is a string, just take it
+				$meta["license"] = $this->config->values["license"];
+			else if(is_array($this->config->values["license"])) // If the license is an array, compose a comma , separated string from it
+			{
+				if(count($this->config->values["license"]) > 0)
+					$meta["license"] = $this->config->values["license"][0];
+
+				for($i = 1; $i < count($this->config->values["license"]); $i++)
+					$meta["license"] .= ", ".$this->config->values["license"][$i];
+			}
+		}
+
+		return new NixAttrSet($meta);
+	}
+
+	private function generatePackageBuild()
+	{
+		return new NixFunInvocation(new NixExpression("composerEnv.buildPackage"), array(
+			"name" => $this->config->packageName,
+			"src" => new NixFile("./."),
+			"executable" => $this->executable,
+			"packages" => new NixInherit(),
+			"devPackages" => new NixInherit(),
+			"noDev" => new NixInherit(),
+			"symlinkDependencies" => $this->symlinkDependencies,
+			"meta" => $this->generatePackageMetaDataExpr()
+		));
+	}
+
+	public function toNixAST()
+	{
+		return new NixFunction(array(
+			"composerEnv" => new NixNoDefault(),
+			"fetchurl" => new NixNoDefault(),
+			"fetchgit" => null,
+			"fetchhg" => null,
+			"fetchsvn" => null,
+			"noDev" => false
+		), new NixLet(array(
+			"packages" => $this->generateDependenciesExpr($this->config->packages),
+			"devPackages" => $this->generateDependenciesExpr($this->config->devPackages)
+		), $this->generatePackageBuild()));
+	}
+}
+?>
diff --git a/src/Composer2Nix/Generator.php b/src/Composer2Nix/Generator.php
index 9975c71..d2c3ef0 100644
--- a/src/Composer2Nix/Generator.php
+++ b/src/Composer2Nix/Generator.php
@@ -2,290 +2,44 @@
 namespace Composer2Nix;
 use Exception;
 use PNDP\NixGenerator;
-use PNDP\AST\NixAttrReference;
-use PNDP\AST\NixAttrSet;
-use PNDP\AST\NixExpression;
-use PNDP\AST\NixFile;
-use PNDP\AST\NixFunction;
-use PNDP\AST\NixFunInvocation;
-use PNDP\AST\NixImport;
-use PNDP\AST\NixInherit;
-use PNDP\AST\NixLet;
-use PNDP\AST\NixNoDefault;
-use PNDP\AST\NixURL;
+use Composer2Nix\Expressions\CompositionExpression;
+use Composer2Nix\Expressions\PackagesExpression;
 
 class Generator
 {
-	private static function selectSourceObject($preferredInstall, $package)
+	private static function writeExprToFile($filename, $expr)
 	{
-		if($preferredInstall === "source")
-		{
-			if(array_key_exists("source", $package))
-				return $package["source"];
-			else if(array_key_exists("dist", $package))
-				return $package["dist"];
-			else
-				throw new Exception("Encountered a dangling package reference");
-		}
-		else
-		{
-			if(array_key_exists("dist", $package))
-				return $package["dist"];
-			else if(array_key_exists("source", $package))
-				return $package["source"];
-			else
-				throw new Exception("Encountered a dangling package reference");
-		}
-	}
-
-	private static function prefixRelativePath($target)
-	{
-		if(substr($target, 0, 1) == "/" || substr($target, 0, 2) == "./" || substr($target, 0, 3) == "../")
-			return $target;
-		else
-			return "./".$target;
-	}
-
-	private static function generatePackagesAttrSet(array $packages, $preferredInstall)
-	{
-		$dependencies = array();
-
-		foreach($packages as $package)
-		{
-			$dependency = array();
-
-			if(array_key_exists("target-dir", $package))
-				$dependency["targetDir"] = $package["target-dir"];
-			else
-				$dependency["targetDir"] = "";
-
-			$sourceObj = Generator::selectSourceObject($preferredInstall, $package);
-
-			switch($sourceObj["type"])
-			{
-				case "path":
-					$dependency["src"] = new NixFile($sourceObj['url']);
-					break;
-
-				case "zip":
-					if($sourceObj["reference"] == "")
-						$reference = "";
-					else
-						$reference = "-".$sourceObj["reference"];
-
-					if(substr($sourceObj["url"], 0, 7) === "http://" || substr($sourceObj["url"], 0, 8) === "https://")
-					{
-						$hash = shell_exec('nix-prefetch-url "'.$sourceObj['url'].'"');
-						$src = new NixFunInvocation(new NixFile("fetchurl"), array(
-							"url" => new NixURL($sourceObj["url"]),
-							"sha256" => substr($hash, 0, -1)
-						));
-					}
-					else
-						$src = new NixFile($sourceObj['url']);
-
-					$dependency["src"] = new NixFunInvocation(new NixExpression("composerEnv.buildZipPackage"), array(
-						"name" => strtr($package["name"], "/", "-").$reference,
-						"src" => $src
-					));
-					break;
-
-				case "git":
-					$outputStr = shell_exec('nix-prefetch-git "'.$sourceObj['url'].'" '.$sourceObj["reference"]);
-
-					$output = json_decode($outputStr, true);
-					$hash = $output["sha256"];
-
-					$dependency["src"] = new NixFunInvocation(new NixExpression("fetchgit"), array(
-						"name" => strtr($package["name"], "/", "-").'-'.$sourceObj["reference"],
-						"url" => $sourceObj["url"],
-						"rev" => $sourceObj["reference"],
-						"sha256" => $hash
-					));
-					break;
-
-				case "hg":
-					$hash = shell_exec('nix-prefetch-hg "'.$sourceObj['url'].'" '.$sourceObj["reference"]);
-					$dependency["src"] = new NixFunInvocation(new NixExpression("fetchhg"), array(
-						"name" => strtr($package["name"], "/", "-").'-'.$sourceObj["reference"],
-						"url" => $sourceObj["url"],
-						"rev" => $sourceObj["reference"],
-						"sha256" => $hash
-					));
-					break;
-
-				case "svn":
-					$hash = shell_exec('nix-prefetch-svn "'.$sourceObj['url'].'" '.$sourceObj["reference"]);
-					$dependency["src"] = new NixFunInvocation(new NixExpression("fetchsvn"), array(
-						"name" => strtr($package["name"], "/", "-").'-'.$sourceObj["reference"],
-						"url" => $sourceObj["url"],
-						"rev" => $sourceObj["reference"],
-						"sha256" => $hash
-					));
-					break;
-
-				default:
-					throw new Exception("Cannot convert dependency of type: ".$sourceObj["type"]);
-			}
-
-			$dependencies[$package["name"]] = $dependency;
-		}
-
-		return new NixAttrSet($dependencies);
-	}
-
-	private static function generatePackagesExpression(array $config, $outputFile, $name, $preferredInstall, array $packages, array $devPackages, $executable, $symlinkDependencies)
-	{
-		$handle = fopen($outputFile, "w");
+		$handle = fopen($filename, "w");
 
 		if($handle === false)
-			throw new Exception("Cannot write to: ".$outputFile);
+			throw new Exception("Cannot write to: ".$filename);
 
-		$packagesAttrSet = Generator::generatePackagesAttrSet($packages, $preferredInstall);
-		$devpackagesAttrSet = Generator::generatePackagesAttrSet($devPackages, $preferredInstall);
-
-		/* Compose meta properties */
-		$meta = array();
-
-		if(array_key_exists("homepage", $config))
-			$meta["homepage"] = $config["homepage"];
-
-		if(array_key_exists("license", $config))
-		{
-			if(is_string($config["license"]))
-				$meta["license"] = $config["license"];
-			else if(is_array($config["license"]))
-			{
-				if(count($config["license"]) > 0)
-					$meta["license"] = $config["license"][0];
-
-				for($i = 1; $i < count($config["license"]); $i++)
-					$meta["license"] .= ", ".$config["license"][$i];
-			}
-		}
-
-		/* Compose package function invocation */
-		$expr = new NixFunction(array(
-			"composerEnv" => new NixNoDefault(),
-			"fetchurl" => new NixNoDefault(),
-			"fetchgit" => null,
-			"fetchhg" => null,
-			"fetchsvn" => null,
-			"noDev" => false
-		), new NixLet(array(
-			"packages" => $packagesAttrSet,
-			"devPackages" => $devpackagesAttrSet
-		), new NixFunInvocation(new NixExpression("composerEnv.buildPackage"), array(
-			"name" => $name,
-			"src" => new NixFile("./."),
-			"executable" => $executable,
-			"packages" => new NixInherit(),
-			"devPackages" => new NixInherit(),
-			"noDev" => new NixInherit(),
-			"symlinkDependencies" => $symlinkDependencies,
-			"meta" => new NixAttrSet($meta)
-		))));
-
-		$exprStr = NixGenerator::phpToNix($expr, true);
-		fwrite($handle, $exprStr);
+		fwrite($handle, NixGenerator::phpToNix($expr, true));
 		fclose($handle);
 	}
 
+	private static function generatePackagesExpression($outputFile, ComposerConfig $config, $executable, $symlinkDependencies, $preferredInstall)
+	{
+		Generator::writeExprToFile($outputFile, new PackagesExpression($config, $executable, $symlinkDependencies, $preferredInstall));
+	}
+
 	private static function generateCompositionExpression($compositionFile, $outputFile, $composerEnvFile)
 	{
-		$handle = fopen($compositionFile, "w");
+		Generator::writeExprToFile($compositionFile, new CompositionExpression($outputFile, $composerEnvFile));
+	}
 
-		if($handle === false)
-			throw new Exception("Cannot write to: ".$compositionFile);
-
-		$expr = new NixFunction(array(
-			"pkgs" => new NixFunInvocation(new NixImport(new NixExpression("<nixpkgs>")), array(
-				"system" => new NixInherit()
-			)),
-			"system" => new NixAttrReference(new NixExpression("builtins"), new NixExpression("currentSystem")),
-			"noDev" => false
-		), new NixLet(array(
-			"composerEnv" => new NixFunInvocation(new NixImport(new NixFile(Generator::prefixRelativePath($composerEnvFile))), array(
-				"stdenv" => new NixInherit("pkgs"),
-				"writeTextFile" => new NixInherit("pkgs"),
-				"fetchurl" => new NixInherit("pkgs"),
-				"php" => new NixInherit("pkgs"),
-				"unzip" => new NixInherit("pkgs")
-			))
-		), new NixFunInvocation(new NixImport(new NixFile(Generator::prefixRelativePath($outputFile))), array(
-			"composerEnv" => new NixInherit(),
-			"noDev" => new NixInherit(),
-			"fetchurl" => new NixInherit("pkgs"),
-			"fetchgit" => new NixInherit("pkgs"),
-			"fetchhg" => new NixInherit("pkgs"),
-			"fetchsvn" => new NixInherit("pkgs")
-		))));
-
-		$exprStr = NixGenerator::phpToNix($expr, true);
-		fwrite($handle, $exprStr);
-		fclose($handle);
+	private static function copyComposerEnv($composerEnvFile, $noCopyComposerEnv)
+	{
+		if(!$noCopyComposerEnv && !copy(dirname(__FILE__)."/composer-env.nix", $composerEnvFile))
+			throw new Exception("Cannot copy composer-env.nix to".$composerEnvFile);
 	}
 
 	public static function generateNixExpressions($name, $executable, $preferredInstall, $noDev, $configFile, $lockFile, $outputFile, $compositionFile, $composerEnvFile, $noCopyComposerEnv, $symlinkDependencies)
 	{
-		/* Open the composer.json file and decode it */
-		$composerJSONStr = file_get_contents($configFile);
-
-		if($composerJSONStr === false)
-			throw new Exception("Cannot open contents of: ".$configFile);
-
-		$config = json_decode($composerJSONStr, true);
-
-		/* If no package name has been provided, attempt to use the name in the composer config file */
-		if($name === null)
-		{
-			if(array_key_exists("name", $config))
-				$name = $config["name"];
-			else
-			{
-				throw new Exception("Cannot determine a package name! Either add a name\n".
-					"property to the composer.json file or provide a --name parameter!");
-			}
-		}
-
-		$name = strtr($name, "/", "-"); // replace / by - since / is not allowed in Nix package names
-
-		/* Open the lock file and decode it */
-
-		if(file_exists($lockFile))
-		{
-			$composerLockStr = file_get_contents($lockFile);
-
-			if($composerLockStr === false)
-				throw new Exception("Cannot open contents of: ".$lockFile);
-
-			$lockConfig = json_decode($composerLockStr, true);
-			
-			if(array_key_exists("packages", $lockConfig))
-				$packages = $lockConfig["packages"];
-			else
-				$packages = array();
-
-			if(!$noDev && array_key_exists("packages-dev", $lockConfig))
-				$devPackages = $lockConfig["packages-dev"];
-			else
-				$devPackages = array();
-		}
-		else
-		{
-			$packages = array();
-			$devPackages = array();
-		}
-
-		/* Generate packages expression */
-		Generator::generatePackagesExpression($config, $outputFile, $name, $preferredInstall, $packages, $devPackages, $executable, $symlinkDependencies);
-
-		/* Generate composition expression */
+		$config = new ComposerConfig($configFile, $lockFile, $name, $noDev);
+		Generator::generatePackagesExpression($outputFile, $config, $executable, $symlinkDependencies, $preferredInstall);
 		Generator::generateCompositionExpression($compositionFile, $outputFile, $composerEnvFile);
-
-		/* Copy composer-env.nix */
-		if(!$noCopyComposerEnv && !copy(dirname(__FILE__)."/composer-env.nix", $composerEnvFile))
-			throw new Exception("Cannot copy composer-env.nix!");
+		Generator::copyComposerEnv($composerEnvFile, $noCopyComposerEnv);
 	}
 }
 ?>
diff --git a/src/Composer2Nix/NixASTNode.php b/src/Composer2Nix/NixASTNode.php
new file mode 100644
index 0000000..241f695
--- /dev/null
+++ b/src/Composer2Nix/NixASTNode.php
@@ -0,0 +1,17 @@
+<?php
+// TODO: move to PNDP
+
+namespace Composer2Nix;
+use PNDP\NixGenerator;
+use PNDP\AST\NixObject;
+
+abstract class NixASTNode extends NixObject
+{
+	abstract public function toNixAST();
+
+	public function toNixExpr($indentLevel, $format)
+	{
+		return NixGenerator::phpToIndentedNix($this->toNixAST(), $indentLevel, $format);
+	}
+}
+?>