diff --git a/src/include/ast.h b/src/include/ast.h
index 4a5814b..31ea3b6 100644
--- a/src/include/ast.h
+++ b/src/include/ast.h
@@ -4,8 +4,18 @@
 #include <stdlib.h>
 
 typedef enum {
-    AST_TYPE_NUM,   // A number.
-    AST_TYPE_CALL,  // A function call.
+    // Primitive types.
+    AST_TYPE_NUM,   // A number (float).
+    AST_TYPE_STR,   // A string
+    AST_TYPE_INT,   // An integer.
+    AST_TYPE_SYM,   // A symbol.
+
+    // Complex types:
+    AST_TYPE_VEC,   // A vector (fixed size, fixed type).
+    AST_TYPE_LIST,  // A list (variable size, variable type).
+
+    // Misc. types.
+    AST_TYP AST_TYPE_CALL,  // A function call.
     AST_TYPE_VDEF,  // A variable definition.
     AST_TYPE_VREF,  // A variable reference.
     AST_TYPE_BLOCK, // A block of code (scope).