diff --git a/src/jasinta.py b/src/jasinta.py
--- a/src/jasinta.py
+++ b/src/jasinta.py
@@ -1,4 +1,4 @@
-from std import lib as stdlib
+from std import lib as stdlib, Number
 
 
 class Undefined:
@@ -10,12 +10,14 @@ def evaluate(node, context):
 		return None
 
 	node_type = node["type"]
+	# retrieve an already existing object from the context
 	if node_type == "Identifier":
 		for ctx in reversed(context):
 			if node["name"] in ctx:
 				return ctx[node["name"]]
 		return Undefined
 
+	# create a new object
 	cls = node_index[node_type]
 	obj = cls(node)
 	return obj.eval(context)
@@ -69,7 +71,7 @@ class BinaryExpression:
 
 		# in fact this doesn't follow JavaScript "+" semantics
 		if self.node["operator"] == "+":
-			return left+right
+			return Number(left.val+right.val)
 		else:
 			raise NotImplementedError
 
@@ -110,7 +112,15 @@ class Literal:
 		self.node = node
 
 	def eval(self, context):
-		return self.node["value"]
+		val = self.node["value"]
+
+		if isinstance(val, float):
+			if int(val) == val:
+				return Number(int(val))
+			else:
+				return Number(val)
+		else:
+			raise NotImplementedError
 
 
 node_index = {cls.__name__: cls for cls in [
diff --git a/src/std.py b/src/std.py
--- a/src/std.py
+++ b/src/std.py
@@ -1,3 +1,8 @@
+class Number:
+	def __init__(self, x):
+		self.val = x
+
+
 lib = {
-	"document": {"write": print}
+	"document": {"write": lambda x: print(x.val)}
 }
diff --git a/tests/test_jasinta.py b/tests/test_jasinta.py
--- a/tests/test_jasinta.py
+++ b/tests/test_jasinta.py
@@ -1,22 +1,18 @@
 from unittest import TestCase
-from unittest.mock import MagicMock
+from unittest.mock import patch
 
 from pyjsparser import parse
 
 from jasinta import interpret
-import std as jasinta_std
 
 
 class TestBasicAddition(TestCase):
-	def setUp(self):
-		self.mock_print = MagicMock()
-		jasinta_std.lib["document"]["write"] = self.mock_print
-
-	def test_interpret(self):
+	@patch("builtins.print")
+	def test_interpret(self, mock_print):
 		s = """var a=3;
 var b=1;
 var c=a+b;
 document.write(c);"""
 
 		interpret(parse(s))
-		self.mock_print.assert_called_with(4.0)
+		mock_print.assert_called_with(4)