diff --git a/README.md b/README.md
index 556461a18..08fa5018c 100644
--- a/README.md
+++ b/README.md
@@ -2,12 +2,12 @@
 
 Golang interpreter written in PHP.
 
-# Example
+## Example
 
 ```php
 use GoPhp\Interpreter;
 
-$interpreter = new Interpreter(<<<GO
+$interp = Interpreter::create(<<<GO
     package main
     
     type person struct {
@@ -29,11 +29,10 @@ $interpreter = new Interpreter(<<<GO
     }
 GO);
 
-$interpreter->run();
+$result = $interp->run();
 ```
 
 See [examples](examples/) for more.
-
 To run examples:
 
 ```
@@ -43,11 +42,9 @@ php main.php
 
 ## WIP
 
-This is a work-in-progress project.
-
-Already implemented:
+This is a toy project, currently work-in-progress.
 
-* see [tests](tests/Functional/files/)
+To see what is already implemented, refer to [tests](tests/Functional/files/).
 
 ## Development
 
@@ -63,4 +60,4 @@ run tests:
 make test
 ```
 
-run `make help` for more commands.
\ No newline at end of file
+run `make help` for more commands.
diff --git a/bin/go-php b/bin/go-php
index 612675167..2f4efad69 100755
--- a/bin/go-php
+++ b/bin/go-php
@@ -184,7 +184,7 @@ function main(array $argv): never
     $stderr = new ResourceOutputStream(STDERR);
     $errorHandler = new OutputToStream($stderr);
 
-    $runtime = new Interpreter(
+    $runtime = Interpreter::create(
         source: $src,
         errorHandler: $errorHandler,
         envVars: new EnvVarSet(
@@ -196,7 +196,7 @@ function main(array $argv): never
 
     $result = $runtime->run();
 
-    exit($result->value);
+    exit($result->exitCode->value);
 }
 
 error_reporting(E_ALL);
diff --git a/examples/helloworld/main.php b/examples/helloworld/main.php
index 71c96ca1d..dfac332ac 100644
--- a/examples/helloworld/main.php
+++ b/examples/helloworld/main.php
@@ -8,7 +8,7 @@
 use GoPhp\Stream\StringStreamProvider;
 
 $stdout = '';
-$interp = new Interpreter(
+$interp = Interpreter::create(
     source: <<<'GO'
         package main
         
@@ -19,7 +19,7 @@
     streams: new StringStreamProvider($stdout, $stdout),
 );
 
-$exitCode = $interp->run();
+$result = $interp->run();
 
 print "Output:\n$stdout\n";
-print "Exit code: $exitCode->value\n";
+print "Exit code: $result->exitCode->value\n";
diff --git a/examples/sorting/main.php b/examples/sorting/main.php
index a266b870f..078b814c7 100644
--- a/examples/sorting/main.php
+++ b/examples/sorting/main.php
@@ -11,16 +11,15 @@
 $goRoot = __DIR__;
 $goFile = __DIR__ . '/src/main.go';
 $goSrc = file_get_contents($goFile);
-
 $stdout = '';
 
-$interp = new Interpreter(
+$interp = Interpreter::create(
     source: $goSrc,
     streams: new StringStreamProvider($stdout, $stdout),
     envVars: new EnvVarSet($goRoot)
 );
 
-$exitCode = $interp->run();
+$result = $interp->run();
 
 print "Output:\n$stdout\n";
-print "Exit code: $exitCode->value\n";
+print "Exit code: $result->exitCode->value\n";
diff --git a/psalm.xml b/psalm.xml
index cdfbfc47f..a4ef816b6 100644
--- a/psalm.xml
+++ b/psalm.xml
@@ -17,6 +17,5 @@
 
     <issueHandlers>
         <ImplicitToStringCast errorLevel="suppress" />
-        <TypeDoesNotContainType errorLevel="suppress" />
     </issueHandlers>
 </psalm>
diff --git a/src/CallStackCollectorDebugger.php b/src/CallStackCollectorDebugger.php
new file mode 100644
index 000000000..9b6f7be20
--- /dev/null
+++ b/src/CallStackCollectorDebugger.php
@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GoPhp;
+
+use GoPhp\Error\PanicError;
+
+use function count;
+use function array_shift;
+
+final class CallStackCollectorDebugger implements Debugger
+{
+    public const DEFAULT_STACK_TRACE_DEPTH = 128;
+
+    /** @var list<InvokableCall|PanicError> */
+    private array $stackTrace = [];
+
+    public function __construct(
+        private readonly bool $enableDebug = true,
+        private readonly int $maxTraceDepth = self::DEFAULT_STACK_TRACE_DEPTH,
+    ) {}
+
+    public function addStackTrace(InvokableCall|PanicError $call): void
+    {
+        if (!$this->enableDebug) {
+            return;
+        }
+
+        $this->stackTrace[] = $call;
+
+        if (count($this->stackTrace) > $this->maxTraceDepth) {
+            array_shift($this->stackTrace);
+        }
+    }
+
+    /**
+     * @return list<InvokableCall|PanicError>
+     */
+    public function getStackTrace(): array
+    {
+        return $this->stackTrace;
+    }
+}
diff --git a/src/Debugger.php b/src/Debugger.php
new file mode 100644
index 000000000..ce66593b2
--- /dev/null
+++ b/src/Debugger.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GoPhp;
+
+use GoPhp\Error\PanicError;
+
+interface Debugger
+{
+    public function addStackTrace(InvokableCall|PanicError $call): void;
+
+    /**
+     * @return list<InvokableCall|PanicError>
+     */
+    public function getStackTrace(): array;
+}
diff --git a/src/Error/InterfaceTypeError.php b/src/Error/InterfaceTypeError.php
index 6eb747046..6ec9acdf0 100644
--- a/src/Error/InterfaceTypeError.php
+++ b/src/Error/InterfaceTypeError.php
@@ -34,7 +34,7 @@ public static function cannotUseAsInterfaceType(WrappedValue|WrappedType $value,
     public static function fromOther(self $error, WrappedType $interfaceType): self
     {
         if (!isset($error->value, $error->missingMethod)) {
-            throw InternalError::unreachable('Cannot convert error from other error');
+            throw InternalError::unreachable('cannot convert error from other error');
         }
 
         return self::cannotUseAsType(
diff --git a/src/GoValue/Slice/SliceValue.php b/src/GoValue/Slice/SliceValue.php
index 1f573430a..b542b68a0 100644
--- a/src/GoValue/Slice/SliceValue.php
+++ b/src/GoValue/Slice/SliceValue.php
@@ -167,7 +167,6 @@ public function append(GoValue $value): void
             $this->grow();
         }
 
-        /** @psalm-suppress PossiblyNullReference */
         $this->values[$this->len++] = $value;
     }
 
@@ -268,6 +267,9 @@ private function exceedsCapacity(): bool
         return $this->len - $this->pos + 1 > $this->cap;
     }
 
+    /**
+     * @psalm-assert !null $this->values
+     */
     private function grow(): void
     {
         $copies = [];
diff --git a/src/Interpreter.php b/src/Interpreter.php
index 3ed477d3d..21bddf6e1 100644
--- a/src/Interpreter.php
+++ b/src/Interpreter.php
@@ -124,104 +124,161 @@
 final class Interpreter
 {
     private static None $noneJump;
+    private readonly JumpStack $jumpStack;
+    private readonly DeferredStack $deferredStack;
+    private readonly ScopeResolver $scopeResolver;
+    private readonly InvokableCallList $initializers;
+    private readonly TypeResolver $typeResolver;
     private Ast $ast;
-    private Iota $iota;
-    private PanicPointer $panicPointer;
-    private Environment $env;
-    private JumpStack $jumpStack;
-    private DeferredStack $deferredStack;
-    private ScopeResolver $scopeResolver;
-    private InvokableCallList $initializers;
     private bool $constContext = false;
     private int $switchContext = 0;
-    private readonly Argv $argv;
-    private readonly ErrorHandler $errorHandler;
     private ?FuncValue $entryPoint = null;
-    private ImportHandler $importHandler;
-    private readonly string $source;
-    private readonly StreamProvider $streams;
-    private readonly FuncTypeValidator $entryPointValidator;
-    private readonly FuncTypeValidator $initValidator;
-    private readonly TypeResolver $typeResolver;
 
-    /**
-     * @param list<GoValue> $argv
-     */
     public function __construct(
-        string $source,
-        array $argv = [],
-        ?BuiltinProvider $builtin = null,
-        ?ErrorHandler $errorHandler = null,
-        StreamProvider $streams = new StdStreamProvider(),
-        FuncTypeValidator $entryPointValidator = new ZeroArityValidator(ENTRY_POINT_FUNC, ENTRY_POINT_PACKAGE),
-        FuncTypeValidator $initValidator = new ZeroArityValidator(INITIALIZER_FUNC),
-        EnvVarSet $envVars = new EnvVarSet(),
-        bool $toplevel = false,
+        private readonly string $source,
+        private readonly Argv $argv,
+        private readonly ErrorHandler $errorHandler,
+        private readonly StreamProvider $streams,
+        private readonly FuncTypeValidator $entryPointValidator,
+        private readonly FuncTypeValidator $initValidator,
+        private readonly ImportHandler $importHandler,
+        private readonly Iota $iota,
+        private PanicPointer $panicPointer,
+        private Environment $env,
+        private readonly ?Debugger $debugger,
     ) {
         $this->jumpStack = new JumpStack();
         $this->deferredStack = new DeferredStack();
         $this->scopeResolver = new ScopeResolver();
         $this->initializers = new InvokableCallList();
-        $this->importHandler = new ImportHandler($envVars);
-        $this->streams = $streams;
-        $this->entryPointValidator = $entryPointValidator;
-        $this->initValidator = $initValidator;
-
-        $this->errorHandler = $errorHandler === null
-            ? new OutputToStream($this->streams->stderr())
-            : $errorHandler;
-
-        if ($builtin === null) {
-            $builtin = new StdBuiltinProvider($this->streams->stderr());
-        }
-
-        $this->iota = $builtin->iota();
-        $this->panicPointer = $builtin->panicPointer();
-        $this->env = Environment::fromEnclosing($builtin->env());
-        $this->argv = (new ArgvBuilder($argv))->build();
-        $this->source = $toplevel ? self::wrapSource($source) : $source;
         $this->typeResolver = new TypeResolver(
             $this->scopeResolver,
             $this->tryEvalConstExpr(...),
             $this->env,
         );
-        self::$noneJump = new None();
     }
 
     /**
-     * @throws InternalError unexpected error during execution
+     * Creates an interpreter instance
+     *
+     * @param string $source Source code to execute
+     * @param array $argv Command line arguments
+     * @param BuiltinProvider|null $builtin Builtin package provider
+     * @param ErrorHandler|null $errorHandler Error handler
+     * @param StreamProvider $streams Stream provider of stdout, stderr, stdin
+     * @param FuncTypeValidator $entryPointValidator Validator for entry point function
+     * @param FuncTypeValidator $initValidator Validator for package initializer functions
+     * @param EnvVarSet $envVars Environment variables
+     * @param bool $toplevel Whether the source is a top level code or not
+     * @param bool $debug Whether to enable debug mode or not
+     * @param Debugger|null $debugger Debugger, if $debug is set to false, this is ignored
+     * @param array $customFileExtensions Custom file extensions to include when importing
+     *
+     * @return self
      */
-    public function run(): ExitCode
+    public static function create(
+        string $source,
+        array $argv = [],
+        ?BuiltinProvider $builtin = null,
+        ?ErrorHandler $errorHandler = null,
+        StreamProvider $streams = new StdStreamProvider(),
+        FuncTypeValidator $entryPointValidator = new ZeroArityValidator(
+            ENTRY_POINT_FUNC,
+            ENTRY_POINT_PACKAGE,
+        ),
+        FuncTypeValidator $initValidator = new ZeroArityValidator(INITIALIZER_FUNC),
+        EnvVarSet $envVars = new EnvVarSet(),
+        bool $toplevel = false,
+        bool $debug = false,
+        ?Debugger $debugger = null,
+        array $customFileExtensions = [],
+    ): self {
+        static $init = false;
+        if (!$init) {
+            $init = true;
+            self::$noneJump = new None();
+        }
+
+        $errorHandler ??= new OutputToStream($streams->stderr());
+        $builtin ??= new StdBuiltinProvider($streams->stderr());
+        $importHandler = new ImportHandler($envVars, $customFileExtensions);
+
+        if ($debug) {
+            $debugger ??= new CallStackCollectorDebugger();
+        } else {
+            $debugger = null;
+        }
+
+        return new self(
+            source: $toplevel ? self::wrapSource($source, $entryPointValidator) : $source,
+            argv: (new ArgvBuilder($argv))->build(),
+            errorHandler: $errorHandler,
+            streams: $streams,
+            entryPointValidator: $entryPointValidator,
+            initValidator: $initValidator,
+            importHandler: $importHandler,
+            iota: $builtin->iota(),
+            panicPointer: $builtin->panicPointer(),
+            env: Environment::fromEnclosing($builtin->env()),
+            debugger: $debugger,
+        );
+    }
+
+    /**
+     * @throws InternalError Unexpected error during execution
+     * @return RuntimeResult Result of execution
+     */
+    public function run(): RuntimeResult
     {
+        $resultBuilder = new RuntimeResultBuilder();
+        if ($this->debugger !== null) {
+            $resultBuilder->setDebugger($this->debugger);
+        }
+
         try {
             $ast = $this->parseSourceToAst($this->source);
             $this->setAst($ast);
             $this->evalDeclsInOrder();
-
-            if ($this->entryPoint === null) {
-                if ($this->scopeResolver->entryPointPackage === $this->entryPointValidator->getPackageName()) {
-                    throw RuntimeError::noEntryPointFunction(
-                        $this->entryPointValidator->getFuncName(),
-                        $this->entryPointValidator->getPackageName(),
-                    );
-                }
-
-                throw RuntimeError::notEntryPointPackage(
-                    $this->scopeResolver->entryPointPackage,
-                    $this->entryPointValidator->getPackageName(),
-                );
-            }
-
+            $this->checkEntryPoint();
             $call = new InvokableCall($this->entryPoint, Argv::fromEmpty());
             $this->callFunc($call);
         } catch (RuntimeError|PanicError $error) {
             $this->errorHandler->onError($error);
-            return ExitCode::Failure;
+            $resultBuilder->setExitCode(ExitCode::Failure);
+            $resultBuilder->setError($error);
+
+            return $resultBuilder->build();
         } catch (AbortExecutionError) {
-            return ExitCode::Failure;
+            $resultBuilder->setExitCode(ExitCode::Failure);
+
+            return $resultBuilder->build();
         }
 
-        return ExitCode::Success;
+        $resultBuilder->setExitCode(ExitCode::Success);
+
+        return $resultBuilder->build();
+    }
+
+    /**
+     * @psalm-assert !null $this->entryPoint
+     */
+    private function checkEntryPoint(): void
+    {
+        if ($this->entryPoint !== null) {
+            return;
+        }
+
+        if ($this->scopeResolver->entryPointPackage === $this->entryPointValidator->getPackageName()) {
+            throw RuntimeError::noEntryPointFunction(
+                $this->entryPointValidator->getFuncName(),
+                $this->entryPointValidator->getPackageName(),
+            );
+        }
+
+        throw RuntimeError::notEntryPointPackage(
+            $this->scopeResolver->entryPointPackage,
+            $this->entryPointValidator->getPackageName(),
+        );
     }
 
     private function evalDeclsInOrder(): void
@@ -626,6 +683,7 @@ private function callFunc(InvokableCall $fn): GoValue
 
         try {
             $value = $fn();
+            $this->debugger?->addStackTrace($fn);
             $this->releaseDeferredStack();
 
             return $value;
@@ -1511,12 +1569,12 @@ private function releaseDeferredStack(): void
         }
     }
 
-    private function wrapSource(string $source): string
+    private static function wrapSource(string $source, FuncTypeValidator $entryPointValidator): string
     {
         return <<<GO
-        package {$this->entryPointValidator->getPackageName()}
+        package {$entryPointValidator->getPackageName()}
         
-        func {$this->entryPointValidator->getFuncName()}() {
+        func {$entryPointValidator->getFuncName()}() {
             {$source}
         }
         GO;
diff --git a/src/PanicPointer.php b/src/PanicPointer.php
index 02dbeebef..82fb20e70 100644
--- a/src/PanicPointer.php
+++ b/src/PanicPointer.php
@@ -8,7 +8,5 @@
 
 final class PanicPointer
 {
-    public function __construct(
-        public ?PanicError $panic = null,
-    ) {}
+    public ?PanicError $panic = null;
 }
diff --git a/src/RuntimeResult.php b/src/RuntimeResult.php
new file mode 100644
index 000000000..a0a6d8d65
--- /dev/null
+++ b/src/RuntimeResult.php
@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GoPhp;
+
+use GoPhp\Error\GoError;
+use GoPhp\GoValue\GoValue;
+
+final class RuntimeResult
+{
+    public function __construct(
+        public readonly ExitCode $exitCode,
+        public readonly ?GoValue $res,
+        public readonly ?Debugger $debugger,
+        public readonly ?GoError $error,
+    ) {}
+}
diff --git a/src/RuntimeResultBuilder.php b/src/RuntimeResultBuilder.php
new file mode 100644
index 000000000..0752c1456
--- /dev/null
+++ b/src/RuntimeResultBuilder.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GoPhp;
+
+use GoPhp\Error\GoError;
+use GoPhp\Error\InternalError;
+use GoPhp\GoValue\GoValue;
+
+final class RuntimeResultBuilder
+{
+    private ?GoValue $result = null;
+    private ?Debugger $debugger = null;
+    private ?GoError $error = null;
+    private ?ExitCode $exitCode = null;
+
+    public function setExitCode(ExitCode $exitCode): void
+    {
+        $this->exitCode = $exitCode;
+    }
+
+    public function setResult(GoValue $result): void
+    {
+        $this->result = $result;
+    }
+
+    public function setDebugger(Debugger $debugger): void
+    {
+        $this->debugger = $debugger;
+    }
+
+    public function setError(GoError $error): void
+    {
+        $this->error = $error;
+    }
+
+    public function build(): RuntimeResult
+    {
+        if ($this->exitCode === null) {
+            throw new InternalError('exit code is not set');
+        }
+
+        return new RuntimeResult(
+            $this->exitCode,
+            $this->result,
+            $this->debugger,
+            $this->error,
+        );
+    }
+}
diff --git a/tests/Functional/InterpreterTest.php b/tests/Functional/InterpreterTest.php
index 2f928eb1a..ece3ec2b1 100644
--- a/tests/Functional/InterpreterTest.php
+++ b/tests/Functional/InterpreterTest.php
@@ -33,7 +33,7 @@ public function testSourceFiles(string $goProgram, string $expectedOutput): void
             $stdin,
         );
 
-        $interpreter = new Interpreter(
+        $interpreter = Interpreter::create(
             source: $goProgram,
             streams: $streams,
             envVars: new EnvVarSet(