diff --git a/include/common/fzl_extern.h b/include/common/fzl_extern.h
index 59971f6..9836114 100644
--- a/include/common/fzl_extern.h
+++ b/include/common/fzl_extern.h
@@ -2,68 +2,82 @@
 #define FZL_EXTERN_H
 
 #include <common/fzl_types.h>
+#include <stdbool.h>
 #include <stddef.h>
 
-// External library entry types
 typedef enum
 {
-  FZL_EXTERN_KIND_PRIMITIVE,
   FZL_EXTERN_KIND_HANDLE,
   FZL_EXTERN_KIND_STRUCT,
   FZL_EXTERN_KIND_REF,
   FZL_EXTERN_KIND_ALIAS,
 } fzl_extern_kind_t;
 
-// External library structure field descriptor
+// Type reference descriptor
+typedef struct
+{
+  bool is_primitive;
+  union
+  {
+    fzl_type_t primitive;
+    size_t type_slot;
+  };
+} fzl_extern_type_ref_t;
+
+// Structure field descriptor
 typedef struct
 {
   char *name;
-  fzl_type_t type;
+  fzl_extern_type_ref_t type;
 } fzl_extern_struct_field_t;
 
-// Extern symbol type descriptor
-typedef struct fzl_extern_type
+// Type descriptor
+typedef struct
 {
   size_t lib_slot;
+  char *name;
   fzl_extern_kind_t kind;
-  char *symbol_name;
-  char *used_name;
 
   union
   {
-    // Structure data
+    // Structure
     struct
     {
-      fzl_extern_struct_field_t **fields;
+      fzl_extern_struct_field_t *fields;
       size_t fields_count;
     } structure;
 
-    // Reference
-    struct fzl_extern_type *ref_of;
+    // Pointer (ref)
+    fzl_extern_type_ref_t ref_target;
 
-    // Aliasing type
-    fzl_type_t alias;
-
-    // Primitive type
-    // NOTE: same type as `.alias` just for readable format
-    fzl_type_t primitive;
+    // Alias
+    fzl_extern_type_ref_t alias_target;
   };
 } fzl_extern_type_t;
 
-// Extern symbol function descriptor
+// Function argument descriptor
+typedef struct
+{
+  char *name;
+  fzl_extern_type_ref_t type;
+  bool is_out;
+} fzl_extern_arg_t;
+
+// Function descriptor
 typedef struct
 {
   size_t lib_slot;
   char *symbol_name;
   char *used_name;
 
-  fzl_extern_type_t *ret_type;
+  bool has_return;
+  fzl_extern_type_ref_t ret_type;
 
-  fzl_extern_type_t **args;
+  fzl_extern_arg_t *args;
   size_t args_count;
 } fzl_extern_fn_t;
 
-// External library descriptor
+// Library descriptor
 typedef struct
 {
   char *name;
diff --git a/include/compiler/fzl_walker.h b/include/compiler/fzl_walker.h
index 8947136..e8aca6d 100644
--- a/include/compiler/fzl_walker.h
+++ b/include/compiler/fzl_walker.h
@@ -1,6 +1,7 @@
 #ifndef FZL_WALKER_H
 #define FZL_WALKER_H
 
+#include <common/fzl_extern.h>
 #include <common/fzl_opcodes.h>
 #include <common/fzl_types.h>
 #include <compiler/fzl_parser.h>
@@ -73,6 +74,15 @@ typedef struct
 
   fzl_ctable_t *classes[64];
   size_t classes_count;
+
+  fzl_extern_lib_t extern_libs[64];
+  size_t extern_libs_count;
+
+  fzl_extern_type_t extern_types[256];
+  size_t extern_types_count;
+
+  fzl_extern_fn_t extern_fns[256];
+  size_t extern_fns_count;
 } fzl_walker_t;
 
 // Allocate new walker
diff --git a/src/compiler/fzl_walker.c b/src/compiler/fzl_walker.c
index 5ddd728..88b51fc 100644
--- a/src/compiler/fzl_walker.c
+++ b/src/compiler/fzl_walker.c
@@ -1,3 +1,4 @@
+#include "common/fzl_extern.h"
 #include <common/fzl_builtins.h>
 #include <common/fzl_opcodes.h>
 #include <common/fzl_types.h>
@@ -61,6 +62,14 @@ fzl_walker_t *fzl_mkwalker(fzl_node_t *root)
   walker->classes_count = 0;
   memset(walker->classes, 0, sizeof(walker->classes));
 
+  walker->extern_libs_count  = 0;
+  walker->extern_types_count = 0;
+  walker->extern_fns_count   = 0;
+
+  memset(walker->extern_libs, 0, sizeof(walker->extern_libs));
+  memset(walker->extern_types, 0, sizeof(walker->extern_types));
+  memset(walker->extern_fns, 0, sizeof(walker->extern_fns));
+
   return walker;
 }
 
@@ -203,7 +212,28 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
   {
     switch (node->type)
     {
-      case FZL_NODETYPE_EXTERN:    // TODO: create meta
+      case FZL_NODETYPE_EXTERN:
+        walker->extern_libs[walker->extern_libs_count++] =
+            (fzl_extern_lib_t){.name = node->ext.libname};
+
+        for (size_t i = 0; i < node->ext.typedefs_count; i++)
+        {
+          fzl_walk_res_t res = walk(walker, node->ext.typedefs[i]);
+          if (res.error)
+            return res;
+        }
+
+        for (size_t i = 0; i < node->ext.fns_count; i++)
+        {
+          fzl_walk_res_t res = walk(walker, node->ext.fns[i]);
+          if (res.error)
+            return res;
+        }
+
+        current_res = (fzl_walk_res_t){
+            .error = false, .type = FZL_TYPE_NULL, .classname = NULL};
+        break;
+
       case FZL_NODETYPE_EXTERN_FN: // TODO: write to meta
       case FZL_NODETYPE_REFERENCE: // TODO: write to meta
       case FZL_NODETYPE_STRUCT:    // TODO: write to meta