diff --git a/src/main/kotlin/function/FunctionNames.java b/src/main/kotlin/function/FunctionNames.java
deleted file mode 100644
index 5e8005b..0000000
--- a/src/main/kotlin/function/FunctionNames.java
+++ /dev/null
@@ -1,13 +0,0 @@
-package function;
-
-import java.lang.annotation.ElementType;
-import java.lang.annotation.Retention;
-import java.lang.annotation.RetentionPolicy;
-import java.lang.annotation.Target;
-
-@Retention(RetentionPolicy.RUNTIME)
-@Target(ElementType.TYPE)
-public @interface FunctionNames {
-
-    String[] value();
-}
diff --git a/src/main/kotlin/function/FunctionNames.kt b/src/main/kotlin/function/FunctionNames.kt
new file mode 100644
index 0000000..cd6394f
--- /dev/null
+++ b/src/main/kotlin/function/FunctionNames.kt
@@ -0,0 +1,10 @@
+package function
+
+import java.lang.annotation.Retention
+import java.lang.annotation.RetentionPolicy.RUNTIME
+import kotlin.annotation.AnnotationTarget.CLASS
+import kotlin.annotation.AnnotationTarget.FILE
+
+@Retention(RUNTIME)
+@Target(CLASS, FILE)
+annotation class FunctionNames(vararg val value: String)
diff --git a/src/main/kotlin/function/LispFunction.java b/src/main/kotlin/function/LispFunction.java
deleted file mode 100644
index bd2c48b..0000000
--- a/src/main/kotlin/function/LispFunction.java
+++ /dev/null
@@ -1,17 +0,0 @@
-package function;
-
-import sexpression.Cons;
-import sexpression.SExpression;
-
-public abstract class LispFunction {
-
-    public abstract SExpression call(Cons argumentList);
-
-    public boolean isArgumentListEvaluated() {
-        return true;
-    }
-
-    public boolean isMacro() {
-        return false;
-    }
-}
diff --git a/src/main/kotlin/function/LispFunction.kt b/src/main/kotlin/function/LispFunction.kt
new file mode 100644
index 0000000..159bdc3
--- /dev/null
+++ b/src/main/kotlin/function/LispFunction.kt
@@ -0,0 +1,15 @@
+package function
+
+import sexpression.Cons
+import sexpression.SExpression
+
+abstract class LispFunction {
+
+    open val isArgumentListEvaluated: Boolean
+        get() = true
+
+    open val isMacro: Boolean
+        get() = false
+
+    abstract fun call(argumentList: Cons): SExpression
+}
diff --git a/src/main/kotlin/function/LispSpecialFunction.java b/src/main/kotlin/function/LispSpecialFunction.java
deleted file mode 100644
index 3b8953d..0000000
--- a/src/main/kotlin/function/LispSpecialFunction.java
+++ /dev/null
@@ -1,9 +0,0 @@
-package function;
-
-public abstract class LispSpecialFunction extends LispFunction {
-
-    @Override
-    public boolean isArgumentListEvaluated() {
-        return false;
-    }
-}
diff --git a/src/main/kotlin/function/LispSpecialFunction.kt b/src/main/kotlin/function/LispSpecialFunction.kt
new file mode 100644
index 0000000..ad55f88
--- /dev/null
+++ b/src/main/kotlin/function/LispSpecialFunction.kt
@@ -0,0 +1,7 @@
+package function
+
+abstract class LispSpecialFunction : LispFunction() {
+
+    override val isArgumentListEvaluated: Boolean
+        get() = false
+}
diff --git a/src/main/kotlin/function/UserDefinedMacro.java b/src/main/kotlin/function/UserDefinedMacro.java
deleted file mode 100644
index 02f0baf..0000000
--- a/src/main/kotlin/function/UserDefinedMacro.java
+++ /dev/null
@@ -1,15 +0,0 @@
-package function;
-
-import sexpression.Cons;
-
-public class UserDefinedMacro extends UserDefinedSpecialFunction {
-
-    public UserDefinedMacro(String name, Cons lambdaList, Cons body) {
-        super(name, lambdaList, body);
-    }
-
-    @Override
-    public boolean isMacro() {
-        return true;
-    }
-}
diff --git a/src/main/kotlin/function/UserDefinedMacro.kt b/src/main/kotlin/function/UserDefinedMacro.kt
new file mode 100644
index 0000000..33671bb
--- /dev/null
+++ b/src/main/kotlin/function/UserDefinedMacro.kt
@@ -0,0 +1,10 @@
+package function
+
+import sexpression.Cons
+
+class UserDefinedMacro(name: String, lambdaList: Cons, body: Cons)
+    : UserDefinedSpecialFunction(name, lambdaList, body) {
+
+    override val isMacro: Boolean
+        get() = true
+}
diff --git a/src/main/kotlin/function/UserDefinedSpecialFunction.java b/src/main/kotlin/function/UserDefinedSpecialFunction.java
deleted file mode 100644
index 848c398..0000000
--- a/src/main/kotlin/function/UserDefinedSpecialFunction.java
+++ /dev/null
@@ -1,15 +0,0 @@
-package function;
-
-import sexpression.Cons;
-
-public class UserDefinedSpecialFunction extends UserDefinedFunction {
-
-    public UserDefinedSpecialFunction(String name, Cons lambdaList, Cons body) {
-        super(name, lambdaList, body);
-    }
-
-    @Override
-    public boolean isArgumentListEvaluated() {
-        return false;
-    }
-}
diff --git a/src/main/kotlin/function/UserDefinedSpecialFunction.kt b/src/main/kotlin/function/UserDefinedSpecialFunction.kt
new file mode 100644
index 0000000..12d82cc
--- /dev/null
+++ b/src/main/kotlin/function/UserDefinedSpecialFunction.kt
@@ -0,0 +1,10 @@
+package function
+
+import sexpression.Cons
+
+open class UserDefinedSpecialFunction(name: String, lambdaList: Cons, body: Cons)
+    : UserDefinedFunction(name, lambdaList, body) {
+
+    override val isArgumentListEvaluated: Boolean
+        get() = false
+}
diff --git a/src/main/kotlin/table/FunctionTable.kt b/src/main/kotlin/table/FunctionTable.kt
index ac58649..10b970d 100644
--- a/src/main/kotlin/table/FunctionTable.kt
+++ b/src/main/kotlin/table/FunctionTable.kt
@@ -124,7 +124,7 @@ object FunctionTable {
             addAllFunctionNamesToTable(function, functionNames.value)
     }
 
-    private fun addAllFunctionNamesToTable(function: Class<out LispFunction>, names: Array<String>) {
+    private fun addAllFunctionNamesToTable(function: Class<out LispFunction>, names: Array<out String>) {
         for (name in names)
             table[name] = createInstance(function, name)
     }