diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..dbce466
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+.vs/
+.vscode/
+build/
+*.cppcheck
+*.dot
+*.png
+*.svg
+*.ps
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2d6d934..8e8a3fe 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -24,6 +24,9 @@ else()
     target_compile_options(Graph PRIVATE -Wall -Wextra -pedantic)
 endif()
 
+# link math
+target_link_libraries(Graph PRIVATE m)
+
 # Optionally, set the output directory for the executable
 # set_target_properties(Graph PROPERTIES
 #     RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/bin"
diff --git a/lex.c b/lex.c
index 37067d5..7283047 100644
--- a/lex.c
+++ b/lex.c
@@ -130,7 +130,7 @@ struct token *lex_token(struct lexer *lex) {
     return &lex->tok;
 }
 
-void lex_print_position(struct lexer *lex) {
+void lex_print_position(const struct lexer *lex) {
     int i;
     int pos = lex->prev_p - lex->start;
     
@@ -146,7 +146,7 @@ void lex_print_position(struct lexer *lex) {
 
 #ifdef LEX_DEBUG
 
-void lex_debug_print_token(struct token *tok) {
+void lex_debug_print_token(const struct token *tok) {
     static const char *token_str[] = {
         "TOK_EOF",
         "TOK_ERROR",
@@ -162,28 +162,30 @@ void lex_debug_print_token(struct token *tok) {
         "TOK_RIGHT_PAREN"
     };
 
-    static const char *fn_str[] = {
-        "FN_ABS",
-        "FN_EXP",
-        "FN_LN",
-        "FN_LOG",
-        "FN_SIN",
-        "FN_COS",
-        "FN_TAN",
-        "FN_ASIN",
-        "FN_ACOS",
-        "FN_ATAN",
-        "FN_SINH",
-        "FN_COSH",
-        "FN_TANH"
-    };
 
     printf("%-20s ", token_str[tok->type]);
 
     if (tok->type == TOK_NUMBER)
         printf("%.2f\n", tok->val.num);
-    else if (tok->type == TOK_FUNCTION)
+    else if (tok->type == TOK_FUNCTION) {
+        static const char *fn_str[] = {
+            "FN_ABS",
+            "FN_EXP",
+            "FN_LN",
+            "FN_LOG",
+            "FN_SIN",
+            "FN_COS",
+            "FN_TAN",
+            "FN_ASIN",
+            "FN_ACOS",
+            "FN_ATAN",
+            "FN_SINH",
+            "FN_COSH",
+            "FN_TANH"
+        };
+
         printf("%s\n", fn_str[tok->val.fn]);
+    }
     else
         printf("\n");
 }
diff --git a/lex.h b/lex.h
index cc5dca6..503660c 100644
--- a/lex.h
+++ b/lex.h
@@ -51,11 +51,11 @@ extern void lex_free(struct lexer *lex);
 extern void lex_next(struct lexer *lex);
 extern struct token *lex_token(struct lexer *lex);
 
-extern void lex_print_position(struct lexer *lex);
+extern void lex_print_position(const struct lexer *lex);
 
 
 #ifdef LEX_DEBUG
-extern void lex_debug_print_token(struct token *tok);
+extern void lex_debug_print_token(const struct token *tok);
 #endif /* LEX_DEBUG */
 
 #endif /* LEX_H */
\ No newline at end of file
diff --git a/main.c b/main.c
index 164963b..c46f9d4 100644
--- a/main.c
+++ b/main.c
@@ -32,9 +32,14 @@ int main(int argc, char *argv[]) {
         file = fopen("out.ps", "w");
         ps_export_graph(file, node, &graph);
         fclose(file);
+
+        file = fopen("graph.dot", "w");
+        node_debug_print_gv(node, file);
+        fclose(file);
+
+        node_free(node);
     }
 
-    node_free(node);
 
     return 0;
 }
\ No newline at end of file
diff --git a/parser.c b/parser.c
index 6855ba4..5c457ce 100644
--- a/parser.c
+++ b/parser.c
@@ -84,8 +84,8 @@ static struct expr_node* parse_bracketed(struct lexer* lex) {
     return node;
 }
 
-static struct expr_node* parse_base(struct lexer* lex) {
-    struct expr_node* inner;
+static struct expr_node *parse_base(struct lexer *lex) {
+    struct expr_node *node, *inner;
 
     if (token_is(lex, TOK_NUMBER)) {
         double val = token_num(lex);
@@ -104,7 +104,11 @@ static struct expr_node* parse_base(struct lexer* lex) {
         if (!(inner = parse_bracketed(lex)))
             return NULL;
 
-        return node_create_fn(fn, inner);
+        if (!(node = node_create_fn(fn, inner))) {
+            node_free(inner);
+        }
+
+        return node;
     }
 
     if (token_is(lex, TOK_LEFT_PAREN)) {
diff --git a/ps_graph.c b/ps_graph.c
index 85ac994..3aea447 100644
--- a/ps_graph.c
+++ b/ps_graph.c
@@ -4,7 +4,7 @@
 #define HALF_GRAPH_SIZE (GRAPH_SIZE / 2)
 #define GRID_STEP (GRAPH_SIZE / 10)
 
-void ps_export_graph(FILE *file, struct expr_node *node, struct graph_range *range) {
+void ps_export_graph(FILE *file, const struct expr_node *node, const struct graph_range *range) {
     int i;
     double x;
     int first = 1;
diff --git a/ps_graph.h b/ps_graph.h
index be4fb6d..2f2ea8f 100644
--- a/ps_graph.h
+++ b/ps_graph.h
@@ -10,6 +10,6 @@ struct graph_range {
 	double step;
 };
 
-extern void ps_export_graph(FILE *file, struct expr_node *node, struct graph_range *range);
+extern void ps_export_graph(FILE *file, const struct expr_node *node, const struct graph_range *range);
 
 #endif
\ No newline at end of file
diff --git a/tree.c b/tree.c
index 6989833..9356611 100644
--- a/tree.c
+++ b/tree.c
@@ -112,22 +112,23 @@ static void debug_print_binop(struct expr_node *node, const char* name, int inde
     debug_print(node->vals.binop.right, indent + 1);
 }
 
+static const char* fn_str[] = {
+    "FN_ABS",
+    "FN_EXP",
+    "FN_LN",
+    "FN_LOG",
+    "FN_SIN",
+    "FN_COS",
+    "FN_TAN",
+    "FN_ASIN",
+    "FN_ACOS",
+    "FN_ATAN",
+    "FN_SINH",
+    "FN_COSH",
+    "FN_TANH"
+};
+
 static void debug_print(struct expr_node *node, int indent) {
-    static const char* fn_str[] = {
-        "FN_ABS",
-        "FN_EXP",
-        "FN_LN",
-        "FN_LOG",
-        "FN_SIN",
-        "FN_COS",
-        "FN_TAN",
-        "FN_ASIN",
-        "FN_ACOS",
-        "FN_ATAN",
-        "FN_SINH",
-        "FN_COSH",
-        "FN_TANH"
-    };
 
     switch (node->type) {
         case EXPR_ADD:
@@ -181,7 +182,72 @@ void node_debug_print(struct expr_node *node) {
     debug_print(node, 0);
 }
 
-double node_eval(struct expr_node *node, double x) {
+static void debug_print_gv(const struct expr_node *node, FILE *output);
+
+static void debug_print_binop_gv(const struct expr_node *node, FILE *output, const char *name) {
+    fprintf(output, "node%p [label=\"%s\"]\n", (void*)node, name);
+    debug_print_gv(node->vals.binop.left, output);
+    debug_print_gv(node->vals.binop.right, output);
+    fprintf(output, "node%p -> node%p [label=left]\n", (void*)node, (void*)node->vals.binop.left);
+    fprintf(output, "node%p -> node%p [label=right]\n", (void*)node, (void*)node->vals.binop.right);
+}
+
+static void debug_print_gv(const struct expr_node *node, FILE *output) {
+
+    switch (node->type) {
+        case EXPR_ADD:
+            debug_print_binop_gv(node, output, "ADD");
+            break;
+
+        case EXPR_SUB:
+            debug_print_binop_gv(node, output, "SUB");
+            break;
+
+        case EXPR_MULT:
+            debug_print_binop_gv(node, output, "MULT");
+            break;
+
+        case EXPR_DIV:
+            debug_print_binop_gv(node, output, "DIV");
+            break;
+
+        case EXPR_POW:
+            debug_print_binop_gv(node, output, "POW");
+            break;
+
+        case EXPR_NEG:
+            fprintf(output, "node%p [label=\"NEG\"]\n", (void*)node);
+            debug_print_gv(node->vals.unop, output);
+            fprintf(output, "node%p -> node%p [label=unop]\n", (void*)node, (void*)node->vals.unop);
+            break;
+
+        case EXPR_CONST:
+            fprintf(output, "node%p [label=\"CONST: %.2f\"]\n", (void*)node, node->vals.num);
+            break;
+
+        case EXPR_X:
+            fprintf(output, "node%p [label=\"X\"]\n", (void*)node);
+            break;
+
+        case EXPR_FN:
+            fprintf(output, "node%p [label=\"FN: %s\"]\n", (void*)node, fn_str[node->vals.fn.fn]);
+            debug_print_gv(node->vals.fn.arg, output);
+            fprintf(output, "node%p -> node%p [label=arg]\n", (void*)node, (void*)node->vals.fn.arg);
+            break;
+
+        default:
+            break;
+    }
+}
+
+void node_debug_print_gv(const struct expr_node *node, FILE *output) {
+    fprintf(output, "digraph G {\n");
+    debug_print_gv(node, output);
+    fprintf(output, "}\n");
+}
+
+
+double node_eval(const struct expr_node *node, double x) {
     switch (node->type) {
         case EXPR_CONST:
             return node->vals.num;
diff --git a/tree.h b/tree.h
index cd9be8f..ff99970 100644
--- a/tree.h
+++ b/tree.h
@@ -42,8 +42,9 @@ extern struct expr_node *node_create_x(void);
 extern struct expr_node *node_create_fn(enum math_fn fn, struct expr_node *arg);
 
 extern void node_debug_print(struct expr_node *node);
+extern void node_debug_print_gv(const struct expr_node *node, FILE *output);
 
-extern double node_eval(struct expr_node *node, double x);
+extern double node_eval(const struct expr_node *node, double x);
 
 extern void node_free(struct expr_node *node);