refactor Function and FunctionBuilder

common/addons/api-terrascript/src/main/java/com/dfsek/terra/addons/terrascript/api/Function.java

@@ -0,0 +1,22 @@
+package com.dfsek.terra.addons.terrascript.api;
+
+import java.util.Map;
+
+public interface Function<T> extends Returnable<T> {
+    Function<?> NULL = new Function<Object>() {
+        @Override
+        public ReturnType returnType() {
+            return null;
+        }
+
+        @Override
+        public Object apply(ImplementationArguments implementationArguments, Map<String, Variable<?>> variableMap) {
+            return null;
+        }
+
+        @Override
+        public Position getPosition() {
+            return null;
+        }
+    };
+}

common/addons/api-terrascript/src/main/java/com/dfsek/terra/addons/terrascript/api/FunctionBuilder.java

@@ -0,0 +1,11 @@
+package com.dfsek.terra.addons.terrascript.api;
+
+import java.util.List;
+
+public interface FunctionBuilder<T extends Function<?>> {
+    T build(List<Returnable<?>> argumentList, Position position) throws ParseException;
+
+    int argNumber();
+
+    Returnable.ReturnType getArgument(int position);
+}