diff --git a/include/evaluator.h b/include/evaluator.h
index e69de29..8e1ea47 100644
--- a/include/evaluator.h
+++ b/include/evaluator.h
@@ -0,0 +1,9 @@
+#ifndef EVALUATOR_H
+#define EVALUATOR_H
+
+#include "lexer.h"
+#include <stdint.h>
+
+uint64_t evaluate(ASTNode *tree);
+
+#endif // !EVALUATOR_H
diff --git a/include/parser.h b/include/parser.h
index 64f5df4..911d964 100644
--- a/include/parser.h
+++ b/include/parser.h
@@ -1,3 +1,6 @@
+#ifndef PARSER_H
+#define PARSER_H
+
 #include "lexer.h"
 #include <stdint.h>
 
@@ -23,3 +26,4 @@ uint8_t node_rbp(ASTNode node);
 AST parse(ASTNodeArray *arr);
 ASTNode *parse_expr(ASTNodeSlice *slice, uint8_t min_bp);
 
+#endif // !PARSER_H
diff --git a/src/evaluator.c b/src/evaluator.c
index e69de29..fc0048d 100644
--- a/src/evaluator.c
+++ b/src/evaluator.c
@@ -0,0 +1,22 @@
+#include "evaluator.h"
+#include "lexer.h"
+#include <stdint.h>
+
+uint64_t evaluate(ASTNode *tree) {
+    if (tree->type == NODE_BINARY_OP) {
+        switch (tree->data.binary.op) {
+            case OP_ADD:
+                return evaluate(tree->data.binary.left) + evaluate(tree->data.binary.left);
+            case OP_SUB:
+                return evaluate(tree->data.binary.left) - evaluate(tree->data.binary.left);
+            case OP_MUL:
+                return evaluate(tree->data.binary.left) * evaluate(tree->data.binary.left);
+            case OP_DIV:
+                return evaluate(tree->data.binary.left) / evaluate(tree->data.binary.left);
+
+        }
+    } else {
+        return tree->data.integer;
+    }
+}
+
diff --git a/test/test_evaluator.c b/test/test_evaluator.c
new file mode 100644
index 0000000..cf97930
--- /dev/null
+++ b/test/test_evaluator.c
@@ -0,0 +1,32 @@
+#include "lexer.h"
+#include "parser.h"
+#include "evaluator.h"
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <setjmp.h>
+#include <cmocka.h>
+#include <stdlib.h>
+
+static void test_basic_evaluation(void** state) {
+    (void) state;
+
+    char expr[256] = "2 + 4 * 40 / 2";
+    ASTNodeArray context;
+
+    tokenize(expr, &context);
+    AST tree = parse(&context);
+    uint64_t value = evaluate(tree.head);
+
+    assert_int_equal(value, 82);
+}
+
+int main(void) {
+    const struct CMUnitTest tests[] = {
+        cmocka_unit_test(test_basic_evaluation),
+    };
+
+    cmocka_run_group_tests(tests, NULL, NULL);
+    return EXIT_SUCCESS;
+}
diff --git a/test/test_parser.c b/test/test_parser.c
index 70e550d..83a6592 100644
--- a/test/test_parser.c
+++ b/test/test_parser.c
@@ -17,34 +17,6 @@ static void test_parsing_basic_expression(void **state) {
     assert_int_equal(tokenize(expr, &tokens), LEXER_OK);
     assert_int_equal(tokens.len, 7);
 
-    ASTNodeArray_get(&tokens, 0, &node);
-    assert_int_equal(node.type, NODE_INTEGER);
-    assert_int_equal(node.data.integer, 2);
-
-    ASTNodeArray_get(&tokens, 1, &node);
-    assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, OP_ADD);
-
-    ASTNodeArray_get(&tokens, 2, &node);
-    assert_int_equal(node.type, NODE_INTEGER);
-    assert_int_equal(node.data.integer, 3);
-
-    ASTNodeArray_get(&tokens, 3, &node);
-    assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, OP_DIV);
-
-    ASTNodeArray_get(&tokens, 4, &node);
-    assert_int_equal(node.type, NODE_INTEGER);
-    assert_int_equal(node.data.integer, 66);
-
-    ASTNodeArray_get(&tokens, 5, &node);
-    assert_int_equal(node.type, NODE_BINARY_OP);
-    assert_int_equal(node.data.binary.op, OP_MUL);
-
-    ASTNodeArray_get(&tokens, 6, &node);
-    assert_int_equal(node.type, NODE_INTEGER);
-    assert_int_equal(node.data.integer, 789);
-
     AST tree = parse(&tokens);
     // Assert head is +
     assert_int_equal(tree.head->type, NODE_BINARY_OP);