diff --git a/src/utils/Makefile.am b/src/utils/Makefile.am
index 600ee40..9fd1be1 100644
--- a/src/utils/Makefile.am
+++ b/src/utils/Makefile.am
@@ -3,6 +3,10 @@ lib_LIBRARIES = libutils.a
 libutils_a_SOURCES =  \
 	string_utils/string_utils.c \
 	ast/ast.c \
+	ast/ast_if.c \
+	ast/ast_command.c \
+	ast/ast_list.c \
+	ast/ast_void.c \
 	lists/lists.c \
 	args/args.c
 
diff --git a/src/utils/ast/ast.h b/src/utils/ast/ast.h
index 64ee195..79eeff3 100644
--- a/src/utils/ast/ast.h
+++ b/src/utils/ast/ast.h
@@ -1,32 +1,12 @@
 #ifndef AST_H
 #define AST_H
 
+#include "utils/ast/ast_base.h"
 #include "utils/ast/ast_command.h"
 #include "utils/ast/ast_if.h"
 #include "utils/ast/ast_list.h"
 #include "utils/ast/ast_void.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;
-};
-
 /* @brief: returns an ast* with corresponding data and type.
  *
  * @note: this function should only be called by ast_create_[TYPE] functions.
@@ -36,6 +16,6 @@ struct ast *ast_create(enum ast_type type, void *data);
 /* @brief: frees the given ast. If ast is NULL, does nothing.
  *
  */
-void ast_free(struct ast *node)
+void ast_free(struct ast *node);
 
 #endif /* ! AST_H */
diff --git a/src/utils/ast/ast_base.h b/src/utils/ast/ast_base.h
new file mode 100644
index 0000000..aa20b76
--- /dev/null
+++ b/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 */
diff --git a/src/utils/ast/ast_command.c b/src/utils/ast/ast_command.c
index a1eafcb..9eb2dd7 100644
--- a/src/utils/ast/ast_command.c
+++ b/src/utils/ast/ast_command.c
@@ -30,8 +30,9 @@ bool ast_is_cmd(struct ast *node)
     return node->type == AST_CMD;
 }
 
-void ast_free_cmd(struct ast_cmd *cmd_data)
+void ast_free_cmd(struct ast_cmd **cmd_data)
 {
-    list_deep_destroy(cmd_data->cmd);
-    free(cmd_data);
+    list_deep_destroy((*cmd_data)->cmd);
+    free(*cmd_data);
+    *cmd_data = NULL;
 }
diff --git a/src/utils/ast/ast_command.h b/src/utils/ast/ast_command.h
index 9a623a8..f7d22a1 100644
--- a/src/utils/ast/ast_command.h
+++ b/src/utils/ast/ast_command.h
@@ -4,7 +4,7 @@
 #include <stdbool.h>
 
 #include "utils/lists/lists.h"
-#include "utils/ast/ast.h"
+#include "utils/ast/ast_base.h"
 
 struct ast_cmd
 {
@@ -28,8 +28,8 @@ struct ast_cmd *ast_get_cmd(struct ast *node);
 struct ast *ast_create_cmd(struct list *cmd);
 
 /*
- * @brief: frees the given ast_cmd.
+ * @brief: frees the given ast_cmd and sets the pointer to NULL.
  */
-void ast_free_cmd(struct ast_cmd *cmd_data)
+void ast_free_cmd(struct ast_cmd **cmd_data);
 
 #endif /* ! AST_COMMAND_H */
diff --git a/src/utils/ast/ast_if.c b/src/utils/ast/ast_if.c
index 50d4c5e..242d5fd 100644
--- a/src/utils/ast/ast_if.c
+++ b/src/utils/ast/ast_if.c
@@ -31,14 +31,15 @@ bool ast_is_if(struct ast *node)
     return node->type == AST_IF;
 }
 
-void ast_free_if(struct ast_if *if_data)
+void ast_free_if(struct ast_if **if_data)
 {
-    if (if_data == NULL)
+    if (if_data == NULL || *if_data == NULL)
         return;
 
-    ast_free(if_data->condition);
-    ast_free(if_data->then_clause);
-    ast_free(if_data->else_clause);
+    ast_free((*if_data)->condition);
+    ast_free((*if_data)->then_clause);
+    ast_free((*if_data)->else_clause);
 
-    free(if_data);
+    free(*if_data);
+    *if_data = NULL;
 }
diff --git a/src/utils/ast/ast_if.h b/src/utils/ast/ast_if.h
index 69d97ec..2036eb7 100644
--- a/src/utils/ast/ast_if.h
+++ b/src/utils/ast/ast_if.h
@@ -3,7 +3,7 @@
 
 #include <stdbool.h>
 
-#include "utils/ast/ast.h"
+#include "utils/ast/ast_base.h"
 
 struct ast_if
 {
@@ -29,8 +29,8 @@ struct ast_if *ast_get_if(struct ast *node);
 struct ast *ast_create_if(struct ast *condition, struct ast *then_clause,
                           struct ast *else_clause);
 /*
- * @brief: frees the given ast_if.
+ * @brief: frees the given ast_if and sets the pointer to NULL.
  */
-void ast_free_if(struct ast_if *if_data)
+void ast_free_if(struct ast_if **if_data);
 
 #endif /* ! AST_IF_H */
diff --git a/src/utils/ast/ast_list.c b/src/utils/ast/ast_list.c
index de178ee..fae1f1a 100644
--- a/src/utils/ast/ast_list.c
+++ b/src/utils/ast/ast_list.c
@@ -1,16 +1,33 @@
 #include "utils/ast/ast.h"
 
-struct ast *ast_create_list(struct list *ast_list);
+struct ast *ast_create_list(struct list *list)
+{
+    struct ast_list *ast_list = malloc(sizeof(struct ast_list));
+    if (ast_list == NULL)
+        return NULL;
 
-struct ast_list *ast_get_list(struct ast *node);
+    ast_list->list = list;
+
+    return ast_create(AST_LIST, ast_list);
+}
+
+struct ast_list *ast_get_list(struct ast *node)
+{
+    assert(node != NULL);
+    return (struct ast_list*)node->data;
+}
 
 bool ast_is_list(struct ast *node)
-
-void ast_free_list(struct ast_list *ast_list)
 {
-    if (ast_list == NULL)
+    return node->type == AST_LIST;
+}
+
+void ast_free_list(struct ast_list **ast_list)
+{
+    if (*ast_list == NULL || ast_list == NULL)
         return;
 
-    list_deep_destroy(ast_list->children);
-    free(ast_list);
+    list_deep_destroy((*ast_list)->children);
+    free(*ast_list);
+    *ast_list = NULL;
 }
diff --git a/src/utils/ast/ast_list.h b/src/utils/ast/ast_list.h
index af7be28..6f1cbd9 100644
--- a/src/utils/ast/ast_list.h
+++ b/src/utils/ast/ast_list.h
@@ -3,7 +3,14 @@
 
 #include <stdbool.h>
 
-#include "utils/ast/ast.h"
+#include "utils/ast/ast_base.h"
+#include "utils/lists/lists.h"
+
+struct ast_list
+{
+    struct list *children; // A list of ASTs (ast*)
+};
+
 
 /**
  * Creates a new AST node representing a list of ASTs
@@ -21,11 +28,10 @@ struct ast_list *ast_get_list(struct ast *node);
  */
 bool ast_is_list(struct ast *node);
 
-struct ast_list
-{
-    struct list *children; // A list of ASTs (ast*)
-};
-
+/* @brief: frees the given ast list.
+ *
+ * @warning: should only be called by ast_free() function.
+ */
 void ast_free_list(struct ast_list *ast_list);
 
 #endif /* ! AST_LIST_H */
diff --git a/src/utils/ast/ast_void.h b/src/utils/ast/ast_void.h
index c3fb123..866a8d8 100644
--- a/src/utils/ast/ast_void.h
+++ b/src/utils/ast/ast_void.h
@@ -4,7 +4,7 @@
 #include <stdbool.h>
 
 #include "utils/lists/lists.h"
-#include "utils/ast/ast.h"
+#include "utils/ast/ast_base.h"
 
 /**
  * Checks if the given AST node is of type AST_VOID.