diff --git a/include/lexer.h b/include/lexer.h
index 943e4a5..d695d16 100644
--- a/include/lexer.h
+++ b/include/lexer.h
@@ -73,5 +73,6 @@ 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);
 bool isoperator(int c);
+Operator char_to_operator(int c);
 
 #endif // !LEXER_H
diff --git a/include/parser.h b/include/parser.h
index e69de29..be689b0 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -0,0 +1,14 @@
+#include "lexer.h"
+
+typedef struct {
+    ASTNode *head;
+} AST;
+
+typedef enum {
+    PARSER_NUD, // Null Denotation
+    PARSER_LED, // Left Denotation
+} ParserState;
+
+size_t node_lbp(Operator op);
+size_t node_rbp(Operator op);
+AST parse(ASTNodeArray arr);
diff --git a/src/lexer.c b/src/lexer.c
index c793c4d..6a1e901 100644
--- a/src/lexer.c
+++ b/src/lexer.c
@@ -141,7 +141,7 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
             }
             ASTNode new_node = {
                 .type = NODE_BINARY_OP,
-                .data.binary.op = current,
+                .data.binary.op = char_to_operator(current),
                 .data.binary.right = NULL,
                 .data.binary.left = NULL,
             };
@@ -158,6 +158,10 @@ LexerErr tokenize(const char *input, ASTNodeArray *out) {
         offset++;
     }
 
+    if (arr.len < 1) {
+        return LEXER_EMPTY_INPUT;
+    }
+
     *out = arr;
     return LEXER_OK;
 }
@@ -225,3 +229,22 @@ bool isoperator(int c) {
             return false;
     }
 }
+
+Operator char_to_operator(int c) {
+    switch (c) {
+        case '+':
+            return OP_ADD;
+            break;
+        case '-':
+            return OP_SUB;
+            break;
+        case '*':
+            return OP_MUL;
+            break;
+        case '/':
+            return OP_DIV;
+            break;
+        default: // I mean shouldn't be used, we assume
+            return -1;
+    }
+}
diff --git a/src/parser.c b/src/parser.c
index e69de29..238cd0a 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -0,0 +1,27 @@
+#include "parser.h"
+#include "lexer.h"
+#include <stdlib.h>
+
+size_t node_lbp(Operator op) {
+    switch (op) {
+        case OP_ADD:
+        case OP_SUB:
+            return 10;
+            break;
+        case OP_DIV:
+        case OP_MUL:
+            return 20;
+    }
+}
+
+size_t node_rbp(Operator op) {
+    switch (op) {
+        case OP_ADD:
+        case OP_SUB:
+            return 10;
+            break;
+        case OP_DIV:
+        case OP_MUL:
+            return 20;
+    }
+}
diff --git a/test/test_lexer.c b/test/test_lexer.c
index 2506441..db9b914 100644
--- a/test/test_lexer.c
+++ b/test/test_lexer.c
@@ -22,7 +22,7 @@ static void test_tokenize_normal_expresion(void **state) {
 
     ASTNodeArray_get(&tokens, 1, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, '+');
+    assert_int_equal(node.data.binary.op, OP_ADD);
 
     ASTNodeArray_get(&tokens, 2, &node);
     assert_int_equal(node.type, NODE_INTEGER);
@@ -30,7 +30,7 @@ static void test_tokenize_normal_expresion(void **state) {
 
     ASTNodeArray_get(&tokens, 3, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, '/');
+    assert_int_equal(node.data.binary.op, OP_DIV);
 
     ASTNodeArray_get(&tokens, 4, &node);
     assert_int_equal(node.type, NODE_INTEGER);
@@ -38,7 +38,7 @@ static void test_tokenize_normal_expresion(void **state) {
 
     ASTNodeArray_get(&tokens, 5, &node);
     assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, '*');
+    assert_int_equal(node.data.binary.op, OP_MUL);
 
     ASTNodeArray_get(&tokens, 6, &node);
     assert_int_equal(node.type, NODE_INTEGER);