diff --git a/examples/arrays.mq b/examples/arrays.mq
new file mode 100644
index 0000000..c7231e8
--- /dev/null
+++ b/examples/arrays.mq
@@ -0,0 +1,11 @@
+var numbers = [1;2;3;4;5];
+
+var for = [array iteration |
+	var iter = [i | if (i < (len array)) [
+		iteration (numbers.i);
+		iter (i+1)
+	]];
+	iter 0
+];
+
+for numbers say;
diff --git a/src/interpreter.cc b/src/interpreter.cc
index 438c6d8..644ac29 100644
--- a/src/interpreter.cc
+++ b/src/interpreter.cc
@@ -95,6 +95,16 @@ Interpreter::Interpreter(std::ostream& out)
 		return {};
 	});
 
+	global.force_define("len", +[](Interpreter &, std::vector<Value> args) -> Result<Value> {
+		assert(args.size() == 1, "len only accepts one argument");
+		assert(args.front().type == Value::Type::Block, "Only blocks can be measure");
+		if (args.front().blk.body.type != Ast::Type::Sequence) {
+			return Value::number(Number(1));
+		} else {
+			return Value::number(Number(args.front().blk.body.arguments.size()));
+		}
+	});
+
 	operators["+"] = binary_operator<std::plus<>>();
 	operators["-"] = binary_operator<std::minus<>>();
 	operators["*"] = binary_operator<std::multiplies<>>();
@@ -107,6 +117,13 @@ Interpreter::Interpreter(std::ostream& out)
 
 	operators["=="] = equality_operator<std::equal_to<>>();
 	operators["!="] = equality_operator<std::not_equal_to<>>();
+
+	operators["."] = +[](Interpreter &i, std::vector<Value> args) -> Result<Value> {
+		assert(args.size() == 2, "Operator . requires two arguments"); // TODO(assert)
+		assert(args.front().type == Value::Type::Block, "Only blocks can be indexed"); // TODO(assert)
+		assert(args.back().type == Value::Type::Number, "Only numbers can be used for indexing"); // TODO(assert)
+		return std::move(args.front()).blk.index(i, std::move(args.back()).n.as_int());
+	};
 }
 
 Result<Value> Interpreter::eval(Ast &&ast)
diff --git a/src/lexer.cc b/src/lexer.cc
index 75f6d76..bbb51fb 100644
--- a/src/lexer.cc
+++ b/src/lexer.cc
@@ -5,8 +5,9 @@
 constexpr std::string_view Notes_Symbols = "abcedefgh";
 constexpr std::string_view Valid_Operator_Chars =
 	"+-*/:%" // arithmetic
-	"|&^"  // logic & bit operations
-	"<>=!" // comparisons
+	"|&^"    // logic & bit operations
+	"<>=!"   // comparisons
+	"."      // indexing
 	;
 
 constexpr auto Keywords = std::array {
@@ -84,14 +85,6 @@ auto Lexer::next_token() -> Result<Token>
 			return { Token::Type::Parameter_Separator, finish(), token_location };
 	}
 
-	// Number literals like .75
-	if (peek() == '.') {
-		consume();
-		while (consume_if(unicode::is_digit)) {}
-		if (token_length != 1)
-			return { Token::Type::Numeric, finish(), token_location };
-	}
-
 	if (consume_if(unicode::is_digit)) {
 		while (consume_if(unicode::is_digit)) {}
 		if (peek() == '.') {
diff --git a/src/musique.hh b/src/musique.hh
index 7a0c7e8..a262ba5 100644
--- a/src/musique.hh
+++ b/src/musique.hh
@@ -444,6 +444,7 @@ struct Block
 	std::shared_ptr<Env> context;
 
 	Result<Value> operator()(Interpreter &i, std::vector<Value> params);
+	Result<Value> index(Interpreter &i, unsigned position);
 };
 
 template<typename T, typename ...XS>
@@ -530,8 +531,13 @@ private:
 
 struct Interpreter
 {
+	/// Output of IO builtins like `say`
 	std::ostream &out;
+
+	/// Operators defined for language
 	std::unordered_map<std::string, Intrinsic> operators;
+
+	/// Current environment (current scope)
 	std::shared_ptr<Env> env;
 
 	Interpreter();
diff --git a/src/tests/lex.cc b/src/tests/lex.cc
index e66a6e0..5178d42 100644
--- a/src/tests/lex.cc
+++ b/src/tests/lex.cc
@@ -114,7 +114,6 @@ suite lexer_test = [] {
 	"Numeric tokens"_test = [] {
 		expect_token_type_and_value(Token::Type::Numeric, "0");
 		expect_token_type_and_value(Token::Type::Numeric, "123456789");
-		expect_token_type_and_value(Token::Type::Numeric, ".75");
 		expect_token_type_and_value(Token::Type::Numeric, "0.75");
 		expect_token_type_and_value(Token::Type::Numeric, "123456789.123456789");
 		expect_token_type_and_value(Token::Type::Numeric, "123.", "123");
diff --git a/src/value.cc b/src/value.cc
index 344212b..878e765 100644
--- a/src/value.cc
+++ b/src/value.cc
@@ -152,3 +152,16 @@ Result<Value> Block::operator()(Interpreter &i, std::vector<Value> arguments)
 	i.env = old_scope;
 	return result;
 }
+
+// TODO Add memoization
+Result<Value> Block::index(Interpreter &i, unsigned position)
+{
+	assert(parameters.size() == 0, "cannot index into block with parameters (for now)");
+	if (body.type != Ast::Type::Sequence) {
+		assert(position == 0, "Out of range"); // TODO(assert)
+		return i.eval((Ast)body);
+	}
+
+	assert(position < body.arguments.size(), "Out of range"); // TODO(assert)
+	return i.eval((Ast)body.arguments[position]);
+}