diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2cffd3d..d300c72 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -31,16 +31,15 @@ add_library(calculator_lib
     src/lexer.c
     src/parser.c
     src/evaluator.c
-    src/ASTNodeArray.c
 )
 
 target_include_directories(calculator_lib
     PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include
 )
 
-# 🔥 aquí está la magia
 target_link_libraries(calculator_lib
     PUBLIC arena
+    PUBLIC arraylist
 )
 
 add_executable(calculator src/main.c)
diff --git a/include/lexer.h b/include/lexer.h
index 9ca60c0..ed8c1e2 100644
--- a/include/lexer.h
+++ b/include/lexer.h
@@ -1,6 +1,7 @@
 #ifndef LEXER_H
 #define LEXER_H
 
+#include "arraylist.h"
 #include <stddef.h>
 #include <stdbool.h>
 #include <stdint.h>
@@ -19,15 +20,6 @@ typedef enum {
     OP_DIV
 } Operator;
 
-typedef enum {
-    ARRAY_OK = 0,
-    ARRAY_NULL,
-    ARRAY_EMPTY,
-    ARRAY_OUT_OF_BOUNDS,
-    ARRAY_NULL_ARG,
-    ARRAY_ALLOC,
-} ASTNodeArrayErr;
-
 typedef enum {
     LEXER_OK = 0,
     LEXER_INT_OVERFLOW,
@@ -52,25 +44,34 @@ typedef struct ASTNode {
     } data;
 } ASTNode;
 
-// I prefer ot have a dynamic array for storing the "tokens"
 typedef struct {
-    size_t len;
-    size_t cap;
-    ASTNode *data;
-} ASTNodeArray;
+    bool is_valid;
+    union {
+        LexerErr err;
+        ArrayList *arr;
+    };
+} TokenizeResult;
 
-ASTNodeArray ASTNodeArray_init(size_t size);
-void ASTNodeArray_free(ASTNodeArray *arr);
-ASTNodeArrayErr ASTNodeArray_push(ASTNodeArray *arr, ASTNode node);
-ASTNodeArrayErr ASTNodeArray_get(const ASTNodeArray *arr, size_t index, ASTNode *out);
-// Out in pop can be NULL so it doesn't return anything
-ASTNodeArrayErr ASTNodeArray_pop(ASTNodeArray *arr, size_t index, ASTNode *out);
-size_t ASTNodeArray_len(ASTNodeArray *arr);
+typedef struct {
+    bool is_valid;
+    union {
+        LexerErr err;
+        ASTNode node;
+    };
+} ASTNodeResult;
+
+typedef struct {
+    bool is_valid;
+    union {
+        LexerErr err;
+        int64_t number;
+    };
+} I64Result;
 
 // Lexer funtions as well as few functionality
-LexerErr tokenize(const char* input, ASTNodeArray *out);
-LexerErr tokenize_number(const char* input, size_t *offset, ASTNode *out);
-LexerErr string_to_integer(const char buf[], int64_t *number);
+TokenizeResult tokenize(const char* input);
+ASTNodeResult tokenize_number(const char* input, size_t *offset);
+I64Result string_to_integer(const char buf[]);
 bool isoperator(int c);
 Operator char_to_operator(int c);
 char operator_to_char(Operator op);
diff --git a/include/parser.h b/include/parser.h
index 7c2fa4f..158b348 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -3,33 +3,39 @@
 
 #include "lexer.h"
 #include "arena.h"
+#include "arraylist.h"
 #include <stdint.h>
 
 typedef struct {
     ASTNode *head;
 } AST;
 
-typedef struct {
-    ASTNodeArray *arr;
-    size_t pos;
-} ASTNodeSlice;
+typedef enum {
+    PARSER_OK = 0,
+    PARSER_UNEXPECTED_TOKEN,
+    PARSER_MISSING_OPERAND,
+    PARSER_UNMATCHED_PAREN,
+    PARSER_OUT_OF_MEMORY,
+} ParserErr;
 
 typedef struct {
-    Arena arena;
-    ASTNode *tree;
+    bool is_valid;
+    union {
+        ParserErr err;
+        struct {
+            Arena arena;
+            ASTNode *tree;
+        };
+    };
 } ParseResult;
 
-ASTNode ASTNodeSlice_peek(ASTNodeSlice *slice);
-ASTNode ASTNodeSlice_next(ASTNodeSlice *slice);
-bool ASTNodeSlice_is_valid(ASTNodeSlice *slice);
-
-ASTNode *nud(ASTNodeSlice *slice);
-ASTNode *led(ASTNodeSlice *slice, size_t right_precedence);
+ASTNode *nud(ArraySlice *slice);
+ASTNode *led(ArraySlice *slice, size_t right_precedence);
 
 uint8_t node_lbp(ASTNode node);
 uint8_t node_rbp(ASTNode node);
 
-ParseResult parse(ASTNodeArray *arr);
-ASTNode *parse_expr(ASTNodeSlice *slice, Arena *arena, uint8_t min_bp);
+ParseResult parse(TokenizeResult tokens);
+ASTNode *parse_expr(ArraySlice *slice, Arena *arena, uint8_t min_bp);
 
 #endif // !PARSER_H
diff --git a/src/ASTNodeArray.c b/src/ASTNodeArray.c
deleted file mode 100644
index a9f2053..0000000
--- a/src/ASTNodeArray.c
+++ /dev/null
@@ -1,108 +0,0 @@
-#include "lexer.h"
-#include <stdlib.h>
-
-#define NODE_ARRAY_DEFAULT_SIZE 64
-// Helps  state machine for the lexer :)
-typedef enum {
-    WAIT_FOR_NUMBER,
-    WAIT_FOR_OPERATOR,
-} LexerState;
-
-ASTNodeArray ASTNodeArray_init(size_t size) {
-    ASTNodeArray new;
-    new.len = 0;      // if 0 then use default
-    new.cap = size == 0 ? NODE_ARRAY_DEFAULT_SIZE : size;
-    new.data = malloc(new.cap * sizeof(ASTNode));
-    return new;
-}
-
-void ASTNodeArray_free(ASTNodeArray *arr) {
-    free(arr->data);
-    arr->cap = 0;
-    arr->len = 0;
-}
-
-ASTNodeArrayErr ASTNodeArray_get(const ASTNodeArray *arr, size_t index, ASTNode *out) {
-    if (arr == NULL) {
-        return ARRAY_NULL;
-    }
-
-    if (out == NULL) {
-        return ARRAY_NULL_ARG;
-    }
-
-    if (arr->len == 0) {
-        return ARRAY_EMPTY;
-    }
-
-    if (index >= arr->len) {
-        return ARRAY_OUT_OF_BOUNDS;
-    }
-
-    *out = arr->data[index];
-
-    return ARRAY_OK;
-}
-
-ASTNodeArrayErr ASTNodeArray_push(ASTNodeArray *arr, ASTNode node) {
-    if (arr == NULL) {
-        return ARRAY_NULL;
-    }
-
-    if (arr->len >= arr->cap) {
-        size_t new_cap = arr->cap * 2;
-        ASTNode *tmp = realloc(arr->data, new_cap * sizeof(ASTNode));
-        if (tmp == NULL) {
-            return ARRAY_ALLOC;
-        }
-        arr->data = tmp;
-        arr->cap = new_cap;
-    }
-
-    arr->data[arr->len] = node;
-    arr->len = arr->len + 1;
-
-    return ARRAY_OK;
-}
-
-ASTNodeArrayErr ASTNodeArray_pop(ASTNodeArray *arr, size_t index, ASTNode *out) {
-    if (arr == NULL) {
-        return ARRAY_NULL;
-    }
-
-    if (arr->len == 0) {
-        return ARRAY_EMPTY;
-    }
-
-    if (index >= arr->len) {
-        return ARRAY_OUT_OF_BOUNDS;
-    }
-
-    if (arr->cap / 4 > arr->len) {
-        size_t new_cap = arr->cap / 2;
-        ASTNode *tmp = realloc(arr->data, new_cap * sizeof(ASTNode));
-        if (tmp == NULL) {
-            return ARRAY_ALLOC;
-        }
-        arr->data = tmp;
-        arr->cap = new_cap;
-    }
-    
-    if (out != NULL) {
-        ASTNode node_to_delete = arr->data[index];
-        *out = node_to_delete;
-    }
-
-    for (size_t i = index; i < arr->len - 1; i++) {
-        arr->data[index] = arr->data[index + 1];
-    }
-
-    return ARRAY_OK;
-}
-
-size_t ASTNodeArray_len(ASTNodeArray *arr) {
-    if (arr == NULL) {
-        return 0;
-    }
-    return arr->len;
-}
diff --git a/src/lexer.c b/src/lexer.c
index 7febdfc..7baf998 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -1,6 +1,7 @@
 #include "lexer.h"
+#include "arraylist.h"
 #include <ctype.h>
-#include <math.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <strings.h>
@@ -12,32 +13,31 @@ typedef enum {
 } LexerState;
 
 
-LexerErr tokenize(const char *input, ASTNodeArray *out) {
+TokenizeResult tokenize(const char *input) {
     size_t offset = 0;
     LexerState state = WAIT_FOR_NUMBER;
-    ASTNodeArray arr = ASTNodeArray_init(0); // 0 defaults to 64
+    ArrayList *arr = arraylist_init(64, sizeof(ASTNode));
 
     while (input[offset] != '\n' && input[offset] != '\0') {
         int current = input[offset];
 
         if (isdigit(current)) {
             if (state != WAIT_FOR_NUMBER) {
-                ASTNodeArray_free(&arr);
-                return LEXER_WRONG_SYNTAX;
+                arraylist_destroy(&arr);
+                return (TokenizeResult) {.is_valid = false, .err = LEXER_WRONG_SYNTAX};
             }
-            ASTNode new_node;
-            LexerErr result = tokenize_number(input, &offset, &new_node);
+            ASTNodeResult result = tokenize_number(input, &offset);
 
-            if (result != LEXER_OK) {
-                ASTNodeArray_free(&arr);
-                return result;
+            if (!result.is_valid) {
+                arraylist_destroy(&arr);
+                return (TokenizeResult) {.is_valid = false, .err = result.err};
             }
 
-            ASTNodeArray_push(&arr, new_node);
+            arraylist_push_back(arr, &result.node);
             state = WAIT_FOR_OPERATOR;
         } else if (isoperator(current)) {
             if (state != WAIT_FOR_OPERATOR) {
-                return LEXER_WRONG_SYNTAX;
+                return (TokenizeResult) {.is_valid = false, .err =LEXER_WRONG_SYNTAX};
             }
             ASTNode new_node = {
                 .type = NODE_BINARY_OP,
@@ -46,29 +46,28 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
                 .data.binary.left = NULL,
             };
 
-            ASTNodeArray_push(&arr, new_node);
+            arraylist_push_back(arr, &new_node);
             state = WAIT_FOR_NUMBER;
         } else if (isspace(current)) {
             // Nothing...
         } else {
-            ASTNodeArray_free(&arr);
-            return LEXER_NOT_RECOGNIZED_SYMBOL;
+            arraylist_destroy(&arr);
+            return (TokenizeResult) {.is_valid = false, .err = LEXER_NOT_RECOGNIZED_SYMBOL};
         }
 
         offset++;
     }
 
-    if (arr.len < 1) {
-        return LEXER_EMPTY_INPUT;
+    if (arraylist_size(arr) < 1) {
+        return (TokenizeResult) {.is_valid = false, .err = LEXER_EMPTY_INPUT};
     }
 
-    *out = arr;
-    return LEXER_OK;
+    return (TokenizeResult) {.is_valid = true, .arr = arr};
 }
 
 // CURRENTLY, it only supports ints, not clear how floating
 // point is implemented but i'll figure it out
-LexerErr tokenize_number(const char *input, size_t *offset, ASTNode *out) {
+ASTNodeResult tokenize_number(const char *input, size_t *offset) {
     char buf[128] = { '\0' };
     size_t buf_pos = 0;
     bool is_integer = true; // Will later be used to differentiate fractions
@@ -78,7 +77,7 @@ LexerErr tokenize_number(const char *input, size_t *offset, ASTNode *out) {
         buf[buf_pos] = input[current];
         
         if (buf_pos >= sizeof(buf)) {
-            return LEXER_BUF_OVERFLOW;
+            return (ASTNodeResult) {.is_valid = false, .err = LEXER_BUF_OVERFLOW};
         }
         current++;
         buf_pos++;
@@ -87,18 +86,19 @@ LexerErr tokenize_number(const char *input, size_t *offset, ASTNode *out) {
     ASTNode new_node;
     if (is_integer) {
         new_node.type = NODE_INTEGER;
-        LexerErr status = string_to_integer(buf, &new_node.data.integer);
-        if (status == LEXER_OK) {
-            *out = new_node;
+        I64Result status = string_to_integer(buf);
+        if (!status.is_valid) {
+            return (ASTNodeResult) {.is_valid = false, .err = status.err};
         }
+        new_node.data.integer = status.number;
         *offset = current;
-        return status;
+        return (ASTNodeResult) {.is_valid = true, .node = new_node};
     }
 
-    return LEXER_FAILED_NUMBER_CONVERSION;
+    return (ASTNodeResult) {.is_valid = false, .err = LEXER_FAILED_NUMBER_CONVERSION};
 }
 
-LexerErr string_to_integer(const char *buf, int64_t *number) {
+I64Result string_to_integer(const char *buf) {
     int c = 0;
     int64_t count = 0;
     while (buf[c] != '\0') {
@@ -106,7 +106,7 @@ LexerErr string_to_integer(const char *buf, int64_t *number) {
         int digit = buf[c] - '0';
 
         if (count > (INT64_MAX - digit) / 10) {
-            return LEXER_INT_OVERFLOW;
+            return (I64Result) {.is_valid = false, .err = LEXER_INT_OVERFLOW};
         }
         count = count * 10;
         count += digit;
@@ -114,8 +114,7 @@ LexerErr string_to_integer(const char *buf, int64_t *number) {
         c++;
     }
 
-    *number = count;
-    return LEXER_OK;
+    return (I64Result) {.is_valid = true, .number = count};
 }
 
 bool isoperator(int c) {
diff --git a/src/main.c b/src/main.c
index 9cc1240..2c5827f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,4 +1,3 @@
-#include "arena.h"
 #include "evaluator.h"
 #include "lexer.h"
 #include "parser.h"
@@ -19,10 +18,9 @@ int main(void) {
     }
     buf[pos] = '\0';
 
-    ASTNodeArray context;
-    tokenize(buf, &context);
+    TokenizeResult tokens = tokenize(buf);
 
-    ParseResult par = parse(&context);
+    ParseResult par = parse(tokens);
     int64_t result = evaluate(par);
 
 
diff --git a/src/parser.c b/src/parser.c
index 9f454ef..a3efae0 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1,4 +1,5 @@
 #include "parser.h"
+#include "arraylist.h"
 #include "lexer.h"
 #include "arena.h"
 #include <stdalign.h>
@@ -41,38 +42,17 @@ uint8_t node_rbp(ASTNode node) {
     }
 }
 
-ASTNode ASTNodeSlice_next(ASTNodeSlice *slice) {
-    return slice->arr->data[slice->pos++];
-}
-
-ASTNode ASTNodeSlice_peek(ASTNodeSlice *slice) {
-    return slice->arr->data[slice->pos];
-}
-
-bool ASTNodeSlice_is_valid(ASTNodeSlice *slice) {
-    if (slice->arr->len < 1) {
-        return false;
-    }
-    if (slice->pos >= slice->arr->len) {
-        return false;
-    }
-
-    return true;
-}
-
-ParseResult parse(ASTNodeArray *arr) {
-    ASTNodeSlice context = {
-        .arr = arr,
-        .pos = 0,
-    };
-    Arena arena = arena_init(sizeof(ASTNode) * arr->len).arena;
+ParseResult parse(TokenizeResult tokens) {
+    ArraySlice *context = arraylist_slice(tokens.arr, 0, arraylist_size(tokens.arr));
+    Arena arena = arena_init(sizeof(ASTNode) * arraylist_size(tokens.arr)).arena;
 
     return (ParseResult) {
+        .is_valid = true,
         .arena = arena,
-        .tree = parse_expr(&context, &arena, 0)};
+        .tree = parse_expr(context, &arena, 0)};
 }
 
-ASTNode *parse_expr(ASTNodeSlice *slice, Arena *arena, uint8_t min_bp) {
+ASTNode *parse_expr(ArraySlice *slice, Arena *arena, uint8_t min_bp) {
     arena_ensure_capacity(
         arena,
         sizeof(ASTNode),
@@ -87,14 +67,15 @@ ASTNode *parse_expr(ASTNodeSlice *slice, Arena *arena, uint8_t min_bp) {
         )
     );
 
-    *left_side = ASTNodeSlice_next(slice);
+    arrayslice_next(slice, left_side);
 
     while (true) {
-        if (!ASTNodeSlice_is_valid(slice)) {
+        if (!arrayslice_is_valid(slice)) {
             break;
         }
 
-        ASTNode operator = ASTNodeSlice_peek(slice);
+        ASTNode operator;
+        arrayslice_peek(slice, &operator);
         uint8_t rbp = node_rbp(operator);
         uint8_t lbp = node_lbp(operator);
 
@@ -102,7 +83,7 @@ ASTNode *parse_expr(ASTNodeSlice *slice, Arena *arena, uint8_t min_bp) {
             break;
         }
 
-        ASTNodeSlice_next(slice);
+        arrayslice_next(slice, NULL);
         ASTNode *right_side = parse_expr(slice, arena, rbp);
 
         arena_ensure_capacity(
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index b48356f..fba3b31 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -1,15 +1,9 @@
 find_package(cmocka REQUIRED)
 
-add_executable(test_nodeArray test_ASTNodeArray.c)
 add_executable(test_lexer test_lexer.c)
 add_executable(test_parser test_parser.c)
 add_executable(test_evaluator test_evaluator.c)
 
-target_link_libraries(test_nodeArray
-    calculator_lib
-    cmocka::cmocka
-)
-
 target_link_libraries(test_lexer
     calculator_lib
     cmocka::cmocka
@@ -25,7 +19,6 @@ target_link_libraries(test_evaluator
     cmocka::cmocka
 )
 
-add_test(NAME nodeArray_tests COMMAND test_nodeArray)
 add_test(NAME lexer_tests COMMAND test_lexer)
 add_test(NAME parser_tests COMMAND test_parser)
 add_test(NAME evaluator_tests COMMAND test_evaluator)
diff --git a/test/test_ASTNodeArray.c b/test/test_ASTNodeArray.c
deleted file mode 100644
index 59c98cb..0000000
--- a/test/test_ASTNodeArray.c
+++ /dev/null
@@ -1,86 +0,0 @@
-#include "lexer.h"
-#include <stdarg.h>
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdint.h>
-#include <setjmp.h>
-#include <cmocka.h>
-
-static void test_array_push(void **state) {
-    (void) state;
-
-    // We use 2 to force resize and checking anything wrong with malloc
-    ASTNodeArray arr = ASTNodeArray_init(2);
-    ASTNode node1 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 90 }
-    };
-
-    ASTNode node2 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 80 }
-    };
-
-    ASTNode node3 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 70 }
-    };
-
-    assert_int_equal(ASTNodeArray_push(&arr, node1), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 1);
-
-    assert_int_equal(ASTNodeArray_push(&arr, node2), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 2);
-
-    assert_int_equal(ASTNodeArray_push(&arr, node3), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 3);
-
-    ASTNodeArray_free(&arr);
-}
-
-static void test_array_pop(void **state) {
-    (void) state;
-
-    // Set to force desize
-    ASTNodeArray arr = ASTNodeArray_init(16);
-    ASTNode node1 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 90 }
-    };
-
-    ASTNode node2 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 80 }
-    };
-
-    ASTNode node3 = {
-        .type = NODE_INTEGER,
-        .data = { .integer = 70 }
-    };
-
-    assert_int_equal(ASTNodeArray_push(&arr, node1), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 1);
-
-    assert_int_equal(ASTNodeArray_push(&arr, node2), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 2);
-
-    assert_int_equal(ASTNodeArray_push(&arr, node3), ARRAY_OK);
-    assert_int_equal(ASTNodeArray_len(&arr), 3);
-
-    ASTNode node4;
-    assert_int_equal(ASTNodeArray_pop(&arr, 1, &node4), ARRAY_OK);
-    assert_int_equal(node4.type, NODE_INTEGER);
-    assert_int_equal(node4.data.integer, 80);
-
-    ASTNodeArray_free(&arr);
-}
-
-
-int main(void) {
-    const struct CMUnitTest tests[] = {
-        cmocka_unit_test(test_array_push),
-        cmocka_unit_test(test_array_pop),
-    };
-
-    return cmocka_run_group_tests(tests, NULL, NULL);
-}
diff --git a/test/test_evaluator.c b/test/test_evaluator.c
index a8f5bd1..c97cdb2 100644
--- a/test/test_evaluator.c
+++ b/test/test_evaluator.c
@@ -13,10 +13,8 @@ static void test_basic_evaluation(void** state) {
     (void) state;
 
     char expr[256] = "2 + 4 * 40 / 2";
-    ASTNodeArray context;
-
-    tokenize(expr, &context);
-    ParseResult result = parse(&context);
+    TokenizeResult tokens = tokenize(expr);
+    ParseResult result = parse(tokens);
     int64_t value = evaluate(result);
 
     assert_int_equal(value, 82);
diff --git a/test/test_lexer.c b/test/test_lexer.c
index db9b914..364ff5b 100644
--- a/test/test_lexer.c
+++ b/test/test_lexer.c
@@ -1,3 +1,4 @@
+#include "arraylist.h"
 #include "lexer.h"
 #include <stdarg.h>
 #include <stdbool.h>
@@ -10,37 +11,37 @@ static void test_tokenize_normal_expresion(void **state) {
     (void) state;
 
     char expr[256] = "2 + 3 / 66 * 789";
-    ASTNodeArray tokens;
     ASTNode node;
-    
-    assert_int_equal(tokenize(expr, &tokens), LEXER_OK);
-    assert_int_equal(tokens.len, 7);
+    TokenizeResult tokens = tokenize(expr);
 
-    ASTNodeArray_get(&tokens, 0, &node);
+    assert_true(tokens.is_valid);
+    assert_int_equal(arraylist_size(tokens.arr), 7);
+
+    arraylist_get(tokens.arr, 0, &node);
     assert_int_equal(node.type, NODE_INTEGER);
     assert_int_equal(node.data.integer, 2);
 
-    ASTNodeArray_get(&tokens, 1, &node);
+    arraylist_get(tokens.arr, 1, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
     assert_int_equal(node.data.binary.op, OP_ADD);
 
-    ASTNodeArray_get(&tokens, 2, &node);
+    arraylist_get(tokens.arr, 2, &node);
     assert_int_equal(node.type, NODE_INTEGER);
     assert_int_equal(node.data.integer, 3);
 
-    ASTNodeArray_get(&tokens, 3, &node);
+    arraylist_get(tokens.arr, 3, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
     assert_int_equal(node.data.binary.op, OP_DIV);
 
-    ASTNodeArray_get(&tokens, 4, &node);
+    arraylist_get(tokens.arr, 4, &node);
     assert_int_equal(node.type, NODE_INTEGER);
     assert_int_equal(node.data.integer, 66);
 
-    ASTNodeArray_get(&tokens, 5, &node);
+    arraylist_get(tokens.arr, 5, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
     assert_int_equal(node.data.binary.op, OP_MUL);
 
-    ASTNodeArray_get(&tokens, 6, &node);
+    arraylist_get(tokens.arr, 6, &node);
     assert_int_equal(node.type, NODE_INTEGER);
     assert_int_equal(node.data.integer, 789);
 }
@@ -49,28 +50,20 @@ static void test_tokenize_unrecognized_symbol(void **state) {
     (void) state;
 
     char expr[256] = " 2 j 3 / 66 } 789";
-    ASTNodeArray tokens = {
-        .len = 0,
-        .cap = 0,
-    };
+    TokenizeResult tokens = tokenize(expr);
 
-    assert_int_equal(tokenize(expr, &tokens), LEXER_NOT_RECOGNIZED_SYMBOL);
-    assert_int_equal(tokens.len, 0);
-    assert_int_equal(tokens.cap, 0);
+    assert_false(tokens.is_valid);
+    assert_uint_equal(tokens.err, LEXER_NOT_RECOGNIZED_SYMBOL);
 }
 
 static void test_tokenize_wrong_sintax(void **state) {
     (void) state;
 
     char expr[256] = "2 3 / 66 789";
-    ASTNodeArray tokens = {
-        .len = 0,
-        .cap = 0,
-    };
+    TokenizeResult tokens = tokenize(expr);
 
-    assert_int_equal(tokenize(expr, &tokens), LEXER_WRONG_SYNTAX);
-    assert_int_equal(tokens.len, 0);
-    assert_int_equal(tokens.cap, 0);
+    assert_false(tokens.is_valid);
+    assert_uint_equal(tokens.err, LEXER_WRONG_SYNTAX);
 }
 
 static void test_string_to_number_normal(void **state) {
@@ -78,23 +71,24 @@ static void test_string_to_number_normal(void **state) {
 
     char num[16] = "2333t55";
     size_t offset = 0;
-    ASTNode result;
+    ASTNodeResult result = tokenize_number(num, &offset);
 
-    assert_int_equal(tokenize_number(num, &offset, &result), LEXER_OK);
+    assert_true(result.is_valid);
 
     assert_int_equal(offset, 4); // equal to t position in string
-    assert_int_equal(result.type, NODE_INTEGER);
-    assert_int_equal(result.data.integer, 2333);
+    assert_int_equal(result.node.type, NODE_INTEGER);
+    assert_int_equal(result.node.data.integer, 2333);
 }
 
 static void test_string_to_number_overflow(void **state) {
     (void) state;
 
-    // Number is INT64_MAX but with a extra 8 at the end
-    char num[32] = "92233720368547758078yy7";
+    // Number is INT64_MAX but with a extra 899 at the end
+    char num[32] = "92233720368547758079";
     size_t offset = 0;
-    ASTNode result;
-    assert_int_equal(tokenize_number(num, &offset, &result), LEXER_INT_OVERFLOW);
+    ASTNodeResult result = tokenize_number(num, &offset);
+    assert_false(result.is_valid);
+    assert_uint_equal(result.err, LEXER_INT_OVERFLOW);
     // Technically it can trigger a buf overflow error but obvioulsy 
     // it will trigger int overflow error first
 }
diff --git a/test/test_parser.c b/test/test_parser.c
index 0fe3c20..c147030 100644
--- a/test/test_parser.c
+++ b/test/test_parser.c
@@ -1,4 +1,5 @@
 #include "arena.h"
+#include "arraylist.h"
 #include "lexer.h"
 #include "parser.h"
 #include <stdarg.h>
@@ -12,13 +13,12 @@ static void test_parsing_basic_expression(void **state) {
     (void) state;
 
     char expr[256] = "2 + 3 / 66 * 789";
-    ASTNodeArray tokens;
-    ASTNode node;
-    
-    assert_int_equal(tokenize(expr, &tokens), LEXER_OK);
-    assert_int_equal(tokens.len, 7);
+    TokenizeResult tokens = tokenize(expr);
 
-    ParseResult result = parse(&tokens);
+    assert_true(tokens.is_valid);
+    assert_int_equal(arraylist_size(tokens.arr), 7);
+
+    ParseResult result = parse(tokens);
     // Assert head is +
     assert_int_equal(result.tree->type, NODE_BINARY_OP);
     assert_int_equal(result.tree->data.binary.op, OP_ADD);