diff --git a/src/lex.c b/src/lex.c
index cca87ab..82ef786 100644
--- a/src/lex.c
+++ b/src/lex.c
@@ -1,5 +1,6 @@
 #include <stdlib.h>
 #include <ctype.h>
+#include <stdbool.h>
 
 #include "lex.h"
 #include "input.h"
@@ -8,72 +9,143 @@
 #include "sym.h"
 #include "ast.h"
 
-bool look_done = false;
-struct Token look_tok;
+#define MAX_IDENTIFIER_LENGTH 256
 
-struct Token lex()
-{
-    int ch;
-    struct Token tok;
+typedef enum {
+    TOKEN_END_OF_PROGRAM,
+    TOKEN_OPERATOR_ADD,
+    TOKEN_OPERATOR_SUB,
+    TOKEN_OPERATOR_MUL,
+    TOKEN_OPERATOR_DIV,
+    TOKEN_LEFT_PARENTHESIS,
+    TOKEN_RIGHT_PARENTHESIS,
+    TOKEN_ASSIGNMENT,
+    TOKEN_SEMICOLON,
+    TOKEN_IDENTIFIER,
+    TOKEN_NUMBER,
+    TOKEN_ERROR
+} TokenType;
 
-    // If lookaheaded 
-    if (look_done) {
-        look_done = false;
+typedef struct {
+    TokenType type;
+    void* attribute;
+    int line;
+    int column;
+    char* error_message;
+} Token;
 
-        return look_tok;    
+typedef struct {
+    char* buffer;
+    int position;
+    int length;
+    int line;
+    int column;
+} InputBuffer;
+
+InputBuffer input_buffer;
+
+void init_input_buffer() {
+    input_buffer.buffer = NULL;
+    input_buffer.position = 0;
+    input_buffer.length = 0;
+    input_buffer.line = 1;
+    input_buffer.column = 0;
+}
+
+void free_input_buffer() {
+    if (input_buffer.buffer != NULL) {
+        free(input_buffer.buffer);
+        input_buffer.buffer = NULL;
+    }
+}
+
+bool load_input_buffer(const char* filename) {
+    free_input_buffer();
+
+    FILE* file = fopen(filename, "rb");
+    if (file == NULL) {
+        return false;
+    }
+
+    fseek(file, 0, SEEK_END);
+    input_buffer.length = ftell(file);
+    fseek(file, 0, SEEK_SET);
+
+    input_buffer.buffer = (char*)malloc(input_buffer.length + 1);
+    if (input_buffer.buffer == NULL) {
+        fclose(file);
+        return false;
+    }
+
+    input_buffer.position = 0;
+    input_buffer.buffer[input_buffer.length] = '\0';
+
+    size_t result = fread(input_buffer.buffer, 1, input_buffer.length, file);
+    fclose(file);
+
+    if (result != input_buffer.length) {
+        free_input_buffer();
+        return false;
+    }
+
+    return true;
+}
+
+int read_char() {
+    if (input_buffer.position >= input_buffer.length) {
+        return EOF;
+    }
+
+    char c = input_buffer.buffer[input_buffer.position++];
+    input_buffer.column++;
+
+    if (c == '\n') {
+        input_buffer.line++;
+        input_buffer.column = 0;
+    }
+
+    return (int)c;
+}
+
+void unread_char(int c) {
+    if (c == EOF) {
+        return;
     }
 
-    eat:
-    switch (ch = fgetc(get_file())) {
-        case ' ': case '\n': goto eat;
-        case EOF: tok.type = EOP; break;
-        case '+': tok.type = OP1; tok.attr = ADD_TYPE; break;
-        case '-': tok.type = OP1; tok.attr = SUB_TYPE; break;
-        case '*': tok.type = OP2; tok.attr = MUL_TYPE; break;
-        case '/': tok.type = OP2; tok.attr = DIV_TYPE; break;       
-        case '(': tok.type = LBR; break;
-        case ')': tok.type = RBR; break;
-        case '=': tok.type = EQ; break;
-        case ';': tok.type = SEM; break;
-        default: 
-            // ID
-            if (isalpha(ch)) {
-                char *id_name = safe_malloc(MAX_LEN);
-                int len = 0;
-                id_name[len++] = ch;
-                do {
-                    if (MAX_LEN == len)
-                        fatal_error("Lexer: Variable name is too long");
-                    id_name[len++] = (ch = fgetc(get_file()));
-                } while (isalpha(ch) || isdigit(ch)); 
-                id_name[len - 1] = '\0';
-            
-                tok.type = ID;
-                tok.attr = add_sym(id_name); 
-
-            // NUM
-            } else if (isdigit(ch)) {
-                int val = ch - '0';
-                while (isdigit(ch = fgetc(get_file())))
-                    val = val * 10 + (ch - '0');
-
-                tok.type = NUM;
-                tok.attr = val;
-            
-            // Error
-            } else {
-                fatal_error("Lexer: Unexpected symbol");
-            }
-
-            ungetc(ch, get_file());
+    input_buffer.position--;
+    input_buffer.column--;
+
+    if (c == '\n') {
+        input_buffer.line--;
+        int i = input_buffer.position - 1;
+        while (i >= 0 && input_buffer.buffer[i] != '\n') {
+            i--;
         }
-    return tok;
+        input_buffer.column = input_buffer.position - i - 1;
+    }
+}
+
+bool is_identifier_start(int c) {
+    return isalpha(c) || c == '_';
 }
 
-struct Token lookahead()
-{
-    look_tok = lex();
-    look_done = true;
+bool is_identifier_body(int c) {
+    return isalnum(c) || c == '_';
+}
+
+Token lex_identifier() {
+    char* buffer = (char*)malloc(MAX_IDENTIFIER_LENGTH + 1);
+    int i = 0;
+
+    int c = read_char();
+    while (is_identifier_body(c) && i < MAX_IDENTIFIER_LENGTH) {
+        buffer[i++] = (char)c;
+        c = read_char();
+    }
+    unread_char(c);
+    buffer[i] = '\0';
 
-    return look_tok;
-}
\ No newline at end of file
+    Token token;
+    token.type = TOKEN_IDENTIFIER;
+    token.attribute = add_sym(buffer);
+    token.line = input
diff --git a/src/sym.c b/src/sym.c
index 9fcbaf5..2ee60b5 100644
--- a/src/sym.c
+++ b/src/sym.c
@@ -5,36 +5,45 @@
 #include "func.h"
 
 struct Table* symbol_table[MAX_SYMBOL_TABLE_SIZE];
-int table_size = 0;
+size_t table_size = 0;
 
-struct Table *get_sym(int id)
+struct Table *get_sym(size_t id)
 {
     return symbol_table[id];
 }
 
-int add_sym(char *name)
+size_t add_sym(const char *name)
 {
-    int i;
-    for (i = 0; i < table_size; i++) {
+    for (size_t i = 0; i < table_size; i++) {
         if (strcmp(symbol_table[i]->name, name) == 0)
             return symbol_table[i]->id;
     }
 
     struct Table *item = safe_malloc(sizeof(struct Table));
+    if (item == NULL) {
+        fprintf(stderr, "Error: Memory allocation failed\n");
+        exit(EXIT_FAILURE);
+    }
+
     item->id = table_size;
-    item->name = name;
+    item->name = safe_malloc(strlen(name) + 1);
+    if (item->name == NULL) {
+        fprintf(stderr, "Error: Memory allocation failed\n");
+        exit(EXIT_FAILURE);
+    }
+    strcpy(item->name, name);
 
     symbol_table[table_size] = item;
 
     return table_size++; 
 }
 
-void set_sym(int id, int val)
+void set_sym(const size_t id, const int val)
 {
     symbol_table[id]->val = val;
 }
 
-int get_table_size()
+size_t get_table_size()
 {
     return table_size;
-}
\ No newline at end of file
+}
diff --git a/src/sym.h b/src/sym.h
index 77a85b1..da85092 100644
--- a/src/sym.h
+++ b/src/sym.h
@@ -1,20 +1,30 @@
-#ifndef SYM_TABLE
-#define SYM_TABLE
+#ifndef SYM_H
+#define SYM_H
 
-#define MAX_SYMBOL_TABLE_SIZE 100
+#include "defs.h"
 
-#include "libtinycompiler_export.h"
+#define MAX_SYMBOL_TABLE_SIZE 1024
 
-struct Table
-{
-    int id;
-    int val;
-    char *name;
+struct Table {
+int id;
+char *name;
+int val;
 };
 
-LIBTINYCOMPILER_EXPORT struct Table *get_sym(int id);
-LIBTINYCOMPILER_EXPORT int add_sym(char *name);
-LIBTINYCOMPILER_EXPORT void set_sym(int id, int val);
-LIBTINYCOMPILER_EXPORT int get_table_size();
+// Returns the symbol table entry with the given id.
+// If the id is out of range, behavior is undefined.
+struct Table *get_sym(int id);
+
+// Adds a symbol to the symbol table and returns its id.
+// If the symbol already exists in the table, returns its existing id.
+// If the symbol table is full, behavior is undefined.
+int add_sym(char *name);
+
+// Sets the value of the symbol with the given id.
+// If the id is out of range, behavior is undefined.
+void set_sym(int id, int val);
+
+// Returns the number of symbols in the symbol table.
+int get_table_size();
 
 #endif
\ No newline at end of file
diff --git a/src/vm.c b/src/vm.c
index 85429cf..bc0fcae 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -1,5 +1,4 @@
 #include <stdio.h>
-
 #include "vm.h"
 #include "stack.h"
 #include "sym.h"
@@ -12,28 +11,52 @@ byte next_byte()
     return *cur_byte++;
 }
 
-void run(byte *code)
+void run(const byte *code)
 {
-    int arg1, arg2;
+    if (code == NULL) {
+        fprintf(stderr, "Error: Byte code is NULL\n");
+        return;
+    }
 
     cur_byte = code;
 
-    next_op:
-    switch (next_byte()) {
-        case PUSH: push(next_byte()); goto next_op;
-        case READ: push(get_sym(next_byte())->val); goto next_op;
-        case WRITE: set_sym(next_byte(), pop()); goto next_op; 
-        case ADD: POP_BOTH; push(arg1 + arg2); goto next_op; 
-        case SUB: POP_BOTH; push(arg1 - arg2); goto next_op;
-        case MUL: POP_BOTH; push(arg1 * arg2); goto next_op;
-        case DIV: POP_BOTH; push(arg1 / arg2); goto next_op;
-        case RET: {
-            int i;
-            for (i = 0; i < get_table_size(); i++) {
-                printf("%s = %i\n", get_sym(i)->name, get_sym(i)->val);
-            }
-        }
+    while (1) {
+        byte opcode = next_byte();
 
-            return;
+        switch (opcode) {
+            case PUSH:
+                push(next_byte());
+                break;
+            case READ:
+                push(get_sym(next_byte())->val);
+                break;
+            case WRITE:
+                set_sym(next_byte(), pop());
+                break; 
+            case ADD:
+                POP_BOTH;
+                push(arg1 + arg2);
+                break; 
+            case SUB:
+                POP_BOTH;
+                push(arg1 - arg2);
+                break;
+            case MUL:
+                POP_BOTH;
+                push(arg1 * arg2);
+                break;
+            case DIV:
+                POP_BOTH;
+                push(arg1 / arg2);
+                break;
+            case RET:
+                for (int i = 0; i < get_table_size(); i++) {
+                    printf("%s = %i\n", get_sym(i)->name, get_sym(i)->val);
+                }
+                return;
+            default:
+                fprintf(stderr, "Error: Unknown opcode %d\n", opcode);
+                return;
+        }
     }
-}
\ No newline at end of file
+}
diff --git a/src/vm.h b/src/vm.h
index 65d1a05..d9db131 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -4,8 +4,13 @@
 #include "libtinycompiler_export.h"
 #include "defs.h"
 
-#define POP_BOTH arg2 = pop(); arg1 = pop()
-
-LIBTINYCOMPILER_EXPORT void run(byte *code);
+/**
+ * Runs the bytecode in the specified code buffer.
+ *
+ * @param code The byte code to execute. This buffer must remain valid throughout
+ *        the execution of the function and must contain a sequence of bytecode
+ *        instructions. If the buffer is NULL or empty, the function has no effect.
+ */
+LIBTINYCOMPILER_EXPORT void run(const byte *code);
 
 #endif
\ No newline at end of file