diff --git a/Makefile b/Makefile
index eb6498f..8ba893c 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@ all: lisp
 CC = gcc
 CFLAGS = -Wall -Wextra
 
-OBJS = enums.c.o main.c.o object.c.o tokens.c.o
+OBJS = enums.c.o lexer.c.o main.c.o object.c.o tokens.c.o
 
 run: lisp
 	./lisp
diff --git a/lexer.c b/lexer.c
new file mode 100644
index 0000000..9d90a39
--- /dev/null
+++ b/lexer.c
@@ -0,0 +1,195 @@
+#include "lexer.h"
+
+#include "enums.h"
+#include "tokens.h"
+
+#include <assert.h>
+#include <ctype.h>
+#include <stdlib.h>
+
+static char buffer[1024];
+static size_t buffer_index = 0;
+static enum State state = STATE_INIT;
+
+static void buffer_add(char chr);
+static void buffer_clean();
+static void token_add(enum State state, char *val);
+
+void buffer_add(char chr)
+{
+    assert(buffer_index < 1000);
+    buffer[buffer_index++] = chr;
+    buffer[buffer_index] = 0;
+}
+
+void buffer_clean()
+{
+    buffer_index = 0;
+}
+
+void token_add(enum State state, char *val)
+{
+    if (state == STATE_WHITESPACE) return;
+
+    enum TokenType token_type;
+    assert(State_to_token_type(state, &token_type));
+
+    tokens_push(token_type, val);
+}
+
+void lex(const char chr)
+{
+    switch (state) {
+    case STATE_INIT:
+        if (chr == '(') {
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (isalpha(chr)) {
+            state = STATE_ATOM;
+            buffer_add(chr);
+        } else if (isdigit(chr)) {
+            state = STATE_NUM;
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    case STATE_WHITESPACE:
+        if (chr == '(') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            buffer_add(chr);
+        } else if (isalpha(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_ATOM;
+            buffer[buffer_index++] = chr;
+        } else if (isdigit(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_NUM;
+            buffer[buffer_index++] = chr;
+        } else {
+            abort();
+        }
+        break;
+    case STATE_OPEN:
+        if (chr == '(') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (isalpha(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_ATOM;
+            buffer_add(chr);
+        } else if (isdigit(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_NUM;
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    case STATE_CLOSE:
+        if (chr == '(') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (isalpha(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_ATOM;
+            buffer_add(chr);
+        } else if (isdigit(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_NUM;
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    case STATE_ATOM:
+        if (chr == '(') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (isalnum(chr)) {
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    case STATE_NUM:
+        if (chr == '(') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_OPEN;
+            buffer_add(chr);
+        } else if (chr == ')') {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_CLOSE;
+            buffer_add(chr);
+        } else if (isspace(chr)) {
+            token_add(state, buffer);
+            buffer_clean();
+            state = STATE_WHITESPACE;
+            buffer_add(chr);
+        } else if (isdigit(chr)) {
+            buffer_add(chr);
+        } else {
+            abort();
+        }
+        break;
+    }
+}
diff --git a/lexer.h b/lexer.h
new file mode 100644
index 0000000..668becd
--- /dev/null
+++ b/lexer.h
@@ -0,0 +1,6 @@
+#ifndef __LEXER_H__
+#define __LEXER_H__
+
+void lex(char chr);
+
+#endif
diff --git a/main.c b/main.c
index 901e039..f831977 100644
--- a/main.c
+++ b/main.c
@@ -1,30 +1,16 @@
 #include "enums.h"
+#include "lexer.h"
 #include "object.h"
 #include "tokens.h"
 
 #include <assert.h>
-#include <ctype.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-static char buffer[1024];
-static size_t buffer_index = 0;
-
-static enum State state = STATE_INIT;
-
 static void error(const char *msg);
 
-/*********
- * Lexer *
- *********/
-
-static void buffer_add(char chr);
-static void buffer_clean();
-static void token_add(enum State state, char *val);
-static void lex(char chr);
-
 /**********
  * Parser *
  **********/
@@ -84,189 +70,6 @@ void error(const char *msg)
     exit(EXIT_FAILURE);
 }
 
-/*********
- * Lexer *
- *********/
-
-void buffer_add(char chr)
-{
-    if (buffer_index >= 1000) error("token too long");
-    buffer[buffer_index++] = chr;
-    buffer[buffer_index] = 0;
-}
-
-void buffer_clean()
-{
-    buffer_index = 0;
-}
-
-void token_add(enum State state, char *val)
-{
-    if (state == STATE_WHITESPACE) return;
-
-    enum TokenType token_type;
-    if (!State_to_token_type(state, &token_type)) error("invalid state");
-
-    tokens_push(token_type, val);
-}
-
-void lex(char chr)
-{
-    switch (state) {
-    case STATE_INIT:
-        if (chr == '(') {
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            state = STATE_WHITESPACE;
-            buffer_add(chr);
-        } else if (isalpha(chr)) {
-            state = STATE_ATOM;
-            buffer_add(chr);
-        } else if (isdigit(chr)) {
-            state = STATE_NUM;
-            buffer_add(chr);
-        } else {
-            error("invalid char (STATE_INIT)");
-        }
-        break;
-    case STATE_WHITESPACE:
-        if (chr == '(') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            buffer_add(chr);
-        } else if (isalpha(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_ATOM;
-            buffer[buffer_index++] = chr;
-        } else if (isdigit(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_NUM;
-            buffer[buffer_index++] = chr;
-        } else {
-            error("invalid char (STATE_WHITESPACE)");
-        }
-        break;
-    case STATE_OPEN:
-        if (chr == '(') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_WHITESPACE;
-            buffer_add(chr);
-        } else if (isalpha(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_ATOM;
-            buffer_add(chr);
-        } else if (isdigit(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_NUM;
-            buffer_add(chr);
-        } else {
-            error("invalid char (STATE_OPEN)");
-        }
-        break;
-    case STATE_CLOSE:
-        if (chr == '(') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_WHITESPACE;
-            buffer_add(chr);
-        } else if (isalpha(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_ATOM;
-            buffer_add(chr);
-        } else if (isdigit(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_NUM;
-            buffer_add(chr);
-        } else {
-            error("invalid char (STATE_CLOSE)");
-        }
-        break;
-    case STATE_ATOM:
-        if (chr == '(') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_WHITESPACE;
-            buffer_add(chr);
-        } else if (isalnum(chr)) {
-            buffer_add(chr);
-        } else {
-            error("invalid char (STATE_ATOM)");
-        }
-        break;
-    case STATE_NUM:
-        if (chr == '(') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_OPEN;
-            buffer_add(chr);
-        } else if (chr == ')') {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_CLOSE;
-            buffer_add(chr);
-        } else if (isspace(chr)) {
-            token_add(state, buffer);
-            buffer_clean();
-            state = STATE_WHITESPACE;
-            buffer_add(chr);
-        } else if (isdigit(chr)) {
-            buffer_add(chr);
-        } else {
-            error("invalid char (STATE_NUM)");
-        }
-        break;
-    }
-}
-
 /**********
  * Parser *
  **********/