diff --git a/modules/collection/build.gradle b/modules/collection/build.gradle
new file mode 100644
index 0000000..e69de29
diff --git a/modules/collection/gradle.properties b/modules/collection/gradle.properties
new file mode 100644
index 0000000..2718f53
--- /dev/null
+++ b/modules/collection/gradle.properties
@@ -0,0 +1,7 @@
+version=0.0.1
+
+pluginVersion=0.1
+pluginId=smnp.collection
+pluginClass=
+pluginProvider=Bartłomiej Pluta
+pluginDependencies=
\ No newline at end of file
diff --git a/modules/collection/src/main/kotlin/io/smnp/ext/CollectionModule.kt b/modules/collection/src/main/kotlin/io/smnp/ext/CollectionModule.kt
new file mode 100644
index 0000000..b25e2e7
--- /dev/null
+++ b/modules/collection/src/main/kotlin/io/smnp/ext/CollectionModule.kt
@@ -0,0 +1,9 @@
+package io.smnp.ext
+
+import org.pf4j.Extension
+
+@Extension
+class CollectionModule : LanguageModuleProvider("smnp.collection") {
+   override fun files() = listOf("list.mus")
+   override fun dependencies() = listOf("smnp.lang")
+}
\ No newline at end of file
diff --git a/modules/collection/src/main/resources/list.mus b/modules/collection/src/main/resources/list.mus
new file mode 100644
index 0000000..8cb54bb
--- /dev/null
+++ b/modules/collection/src/main/resources/list.mus
@@ -0,0 +1,15 @@
+function flatten(...lists: list) {
+    return _flatten(lists as list ^ _flatten(list, []), []);
+}
+
+function _flatten(list: list, output: list) {
+    list as element ^ {
+        if (typeOf(element) == "list") {
+            output = _flatten(element, output);
+        } else {
+            output = output + [element];
+        }
+    }
+
+    return output;
+}
\ No newline at end of file
diff --git a/modules/debug/build.gradle b/modules/debug/build.gradle
new file mode 100644
index 0000000..e69de29
diff --git a/modules/debug/gradle.properties b/modules/debug/gradle.properties
new file mode 100644
index 0000000..8d4e5ea
--- /dev/null
+++ b/modules/debug/gradle.properties
@@ -0,0 +1,7 @@
+version=0.0.1
+
+pluginVersion=0.1
+pluginId=smnp.lang.debug
+pluginClass=
+pluginProvider=Bartłomiej Pluta
+pluginDependencies=
\ No newline at end of file
diff --git a/modules/debug/src/main/kotlin/io/smnp/ext/DebugModule.kt b/modules/debug/src/main/kotlin/io/smnp/ext/DebugModule.kt
new file mode 100644
index 0000000..9e943b6
--- /dev/null
+++ b/modules/debug/src/main/kotlin/io/smnp/ext/DebugModule.kt
@@ -0,0 +1,9 @@
+package io.smnp.ext
+
+import io.smnp.ext.function.CallStackFunction
+import org.pf4j.Extension
+
+@Extension
+class DebugModule : NativeModuleProvider("smnp.lang.debug") {
+   override fun functions() = listOf(CallStackFunction())
+}
\ No newline at end of file
diff --git a/modules/debug/src/main/kotlin/io/smnp/ext/function/CallStackFunction.kt b/modules/debug/src/main/kotlin/io/smnp/ext/function/CallStackFunction.kt
new file mode 100644
index 0000000..24bce6e
--- /dev/null
+++ b/modules/debug/src/main/kotlin/io/smnp/ext/function/CallStackFunction.kt
@@ -0,0 +1,15 @@
+package io.smnp.ext.function
+
+import io.smnp.callable.function.Function
+import io.smnp.callable.function.FunctionDefinitionTool
+import io.smnp.callable.signature.Signature
+import io.smnp.type.model.Value
+
+class CallStackFunction : Function("callstack") {
+   override fun define(new: FunctionDefinitionTool) {
+      new function Signature.simple() body { env, _ ->
+         env.printCallStack()
+         Value.void()
+      }
+   }
+}
\ No newline at end of file
diff --git a/modules/lang/src/main/kotlin/io/smnp/ext/lang/LangModule.kt b/modules/lang/src/main/kotlin/io/smnp/ext/lang/LangModule.kt
index 17883a8..c1d1abc 100644
--- a/modules/lang/src/main/kotlin/io/smnp/ext/lang/LangModule.kt
+++ b/modules/lang/src/main/kotlin/io/smnp/ext/lang/LangModule.kt
@@ -1,13 +1,13 @@
 package io.smnp.ext.lang
 
 import io.smnp.ext.NativeModuleProvider
-import io.smnp.ext.lang.function.DebugFunction
+import io.smnp.ext.lang.function.TypeOfFunction
 import io.smnp.ext.lang.method.ListAccessMethod
 import io.smnp.ext.lang.method.MapAccessMethod
 import org.pf4j.Extension
 
 @Extension
 class LangModule : NativeModuleProvider("smnp.lang") {
-    override fun functions() = listOf(DebugFunction())
+    override fun functions() = listOf(TypeOfFunction())
     override fun methods() = listOf(ListAccessMethod(), MapAccessMethod())
 }
\ No newline at end of file
diff --git a/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/DebugFunction.kt b/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/DebugFunction.kt
deleted file mode 100644
index a91dd59..0000000
--- a/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/DebugFunction.kt
+++ /dev/null
@@ -1,15 +0,0 @@
-package io.smnp.ext.lang.function
-
-import io.smnp.callable.function.Function
-import io.smnp.callable.function.FunctionDefinitionTool
-import io.smnp.callable.signature.Signature.Companion.simple
-import io.smnp.type.model.Value
-
-class DebugFunction : Function("debug") {
-    override fun define(new: FunctionDefinitionTool) {
-        new function simple() body { env, _ ->
-            env.printCallStack()
-            Value.void()
-        }
-    }
-}
\ No newline at end of file
diff --git a/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/TypeOfFunction.kt b/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/TypeOfFunction.kt
new file mode 100644
index 0000000..bef2fa1
--- /dev/null
+++ b/modules/lang/src/main/kotlin/io/smnp/ext/lang/function/TypeOfFunction.kt
@@ -0,0 +1,15 @@
+package io.smnp.ext.lang.function
+
+import io.smnp.callable.function.Function
+import io.smnp.callable.function.FunctionDefinitionTool
+import io.smnp.callable.signature.Signature.Companion.simple
+import io.smnp.type.matcher.Matcher.Companion.allTypes
+import io.smnp.type.model.Value
+
+class TypeOfFunction : Function("typeOf") {
+   override fun define(new: FunctionDefinitionTool) {
+      new function simple(allTypes()) body { _, (obj) ->
+         Value.string(obj.type.toString()) // TODO
+      }
+   }
+}
\ No newline at end of file
diff --git a/settings.gradle b/settings.gradle
index f409ff9..c0802dd 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -4,4 +4,6 @@ include 'app'
 include 'modules'
 
 include 'modules:lang'
-include 'modules:io'
\ No newline at end of file
+include 'modules:debug'
+include 'modules:io'
+include 'modules:collection'
\ No newline at end of file