You can use compiler_interface hpp outside

base.cpp

@@ -1,3 +1,4 @@
+#define CORE_BASE
 
 #if defined(__clang__)
 # define COMPILER_CLANG 1

build.bat

@@ -5,8 +5,9 @@ rem cl main.cpp -I.. user32.lib
 clang core_main.cpp -O0 -Wall -Wno-unused-function -fno-exceptions -fdiagnostics-absolute-paths -g -o main.exe -Wl,user32.lib
 rem ubuntu run clang core_main.cpp -O0 -Wall -Wno-unused-function -fno-exceptions -fdiagnostics-absolute-paths -g -o core.out
 
-rem main.exe -testing
+clang test.cpp
 
+rem main.exe -testing
 rem echo Building arms race
 rem call examples/arms_race/build_arms_race.bat
 rem main examples/arms_race/arms_race.core

core_compiler_interface.hpp

@@ -11,8 +11,8 @@ struct Ast_Lambda;
 struct Ast_Type;
 struct Ast_Expr;
 
-#ifndef CORE_STRINGS
+#ifndef CORE_BASE
-#define CORE_STRINGS
+#define CORE_BASE
 struct String{
   uint8_t *str;
   int64_t len;
@@ -25,6 +25,33 @@ union Intern_String{  // Basically just String
     int64_t len; 
   };
 };
+
+template<class T>
+struct Array {
+  void *allocator;
+  T  *data;
+  int64_t cap;
+  int64_t len;
+};
+
+template<class T>
+struct List_Node{
+  List_Node<T> *next;
+  List_Node<T> *prev;
+  int cap;
+  int len;
+  T data[];
+};
+
+template<class T>
+struct List{
+  int block_size            = 0;
+  int allocation_multiplier = 0;
+  List_Node<T> *first       = 0;
+  List_Node<T> *last        = 0;
+  List_Node<T> *first_free  = 0;
+};
+
 #endif
 
 enum Token_Kind{