refactor(ast): one file per ast_type -- FINISHED

src/utils/ast/ast_base.h

@@ -0,0 +1,25 @@
+#ifndef AST_BASE_H
+#define AST_BASE_H
+
+enum ast_type
+{
+    AST_END,
+    AST_LIST,
+    AST_IF,
+    AST_CMD
+};
+
+struct ast
+{
+    enum ast_type type;
+
+    /**
+     * Data associated with this AST node. It can be one of the following:
+     * - NULL (AST_END)
+     * - struct ast_if* (AST_IF)
+     * - struct ast_cmd* (AST_CMD)
+     */
+    void *data;
+};
+
+#endif /* ! AST_BASE_H */