diff --git a/musique/format.cc b/musique/format.cc
index f35d1de..9ba9b07 100644
--- a/musique/format.cc
+++ b/musique/format.cc
@@ -19,6 +19,7 @@ Value_Formatter Value_Formatter::nest(Context nested) const
 
 std::optional<Error> Value_Formatter::format(std::ostream& os, Interpreter &interpreter, Value const& value)
 {
+	static_assert(requires { os << value; });
 	return std::visit(Overloaded {
 		[&](Intrinsic const& intrinsic) -> std::optional<Error> {
 			for (auto const& [key, val] : Env::global->variables) {
@@ -48,6 +49,9 @@ std::optional<Error> Value_Formatter::format(std::ostream& os, Interpreter &inte
 			return {};
 		},
 		[&](Block const& block) -> std::optional<Error> {
+			if (block.body.arguments.front().type == Ast::Type::Concurrent)
+				unimplemented("Nice printing of concurrent blocks is not implemented yet");
+
 			if (block.is_collection()) {
 				os << '(';
 				for (auto i = 0u; i < block.size(); ++i) {
@@ -62,6 +66,17 @@ std::optional<Error> Value_Formatter::format(std::ostream& os, Interpreter &inte
 			}
 			return {};
 		},
+		[&](Set const& set) -> std::optional<Error> {
+			os << '{';
+			for (auto it = set.elements.begin(); it != set.elements.end(); ++it) {
+				if (it != set.elements.begin()) {
+					os << ", ";
+				}
+				Try(nest(Inside_Block).format(os, interpreter, *it));
+			}
+			os << '}';
+			return {};
+		},
 		[&](auto&&) -> std::optional<Error> {
 			os << value;
 			return {};
diff --git a/musique/interpreter/builtin_functions.cc b/musique/interpreter/builtin_functions.cc
index 04a5fea..38d236d 100644
--- a/musique/interpreter/builtin_functions.cc
+++ b/musique/interpreter/builtin_functions.cc
@@ -838,6 +838,14 @@ static Result<Value> builtin_flat(Interpreter &i, std::vector<Value> args)
 	return Try(into_flat_array(i, std::move(args)));
 }
 
+/// Constructs set from given arguments
+static Result<Value> builtin_set(Interpreter&, std::vector<Value> args)
+{
+	Set set;
+	std::move(args.begin(), args.end(), std::inserter(set.elements, set.elements.end()));
+	return set;
+}
+
 /// Pick random value from arugments
 static Result<Value> builtin_pick(Interpreter &i, std::vector<Value> args)
 {
@@ -1154,6 +1162,7 @@ void Interpreter::register_builtin_functions()
 	global.force_define("rotate",         builtin_rotate);
 	global.force_define("round",          apply_numeric_transform<&Number::round>);
 	global.force_define("scan",           builtin_scan);
+	global.force_define("set",            builtin_set);
 	global.force_define("set_len",        builtin_set_len);
 	global.force_define("set_oct",        builtin_set_oct);
 	global.force_define("shuffle",        builtin_shuffle);
diff --git a/musique/interpreter/interpreter.cc b/musique/interpreter/interpreter.cc
index ff59be8..36271fb 100644
--- a/musique/interpreter/interpreter.cc
+++ b/musique/interpreter/interpreter.cc
@@ -448,7 +448,8 @@ static void snapshot(std::ostream& out, Value const& value) {
 			out << ")";
 		},
 		[](Intrinsic const&) { unreachable(); },
-		[](Macro const&) { unreachable(); }
+		[](Macro const&) { unreachable(); },
+		[](Set const&) { unimplemented("Snapshoting is not supported yet"); }
 	}, value.data);
 }
 
diff --git a/musique/value/array.hh b/musique/value/array.hh
index 8869224..8c0a167 100644
--- a/musique/value/array.hh
+++ b/musique/value/array.hh
@@ -8,6 +8,8 @@
 struct Interpreter;
 struct Value;
 
+// TODO Array should have an ability to be invoked with duration parameter like singular note
+
 /// Eager Array
 struct Array : Collection
 {
diff --git a/musique/value/block.hh b/musique/value/block.hh
index ae5aad7..a545d35 100644
--- a/musique/value/block.hh
+++ b/musique/value/block.hh
@@ -11,6 +11,8 @@ struct Env;
 struct Interpreter;
 struct Value;
 
+// TODO Block should have an ability to be invoked with duration parameter like singular note
+
 /// Lazy Array / Continuation / Closure type thingy
 struct Block : Collection, Function
 {
diff --git a/musique/value/hash.cc b/musique/value/hash.cc
new file mode 100644
index 0000000..5722e89
--- /dev/null
+++ b/musique/value/hash.cc
@@ -0,0 +1,50 @@
+#include <musique/value/hash.hh>
+#include <musique/value/value.hh>
+
+size_t std::hash<Set>::operator()(Set const& set) const noexcept
+{
+	return std::accumulate(
+		set.elements.cbegin(), set.elements.cend(),
+		size_t(0),
+		[](size_t hash, Value const& element) {
+			return hash_combine(hash, std::hash<Value>{}(element));
+		}
+	);
+}
+
+std::size_t std::hash<Value>::operator()(Value const& value) const noexcept
+{
+	auto const value_hash = std::visit(Overloaded {
+		[](Nil) {
+			return std::size_t(0);
+		},
+
+		[](Intrinsic i) {
+			return size_t(i.function_pointer);
+		},
+
+		[](Block const& b) {
+			return hash_combine(std::hash<Ast>{}(b.body), b.parameters.size());
+		},
+
+		[this](Array const& array) {
+			return std::accumulate(
+				array.elements.begin(), array.elements.end(), size_t(0),
+				[this](size_t h, Value const& v) { return hash_combine(h, operator()(v)); }
+			);
+		},
+
+		[](Chord const& chord) {
+			return std::accumulate(chord.notes.begin(), chord.notes.end(), size_t(0), [](size_t h, Note const& n) {
+				h = hash_combine(h, std::hash<std::optional<int>>{}(n.base));
+				h = hash_combine(h, std::hash<std::optional<Number>>{}(n.length));
+				h = hash_combine(h, std::hash<std::optional<i8>>{}(n.octave));
+				return h;
+			});
+		},
+
+		[]<typename T>(T const& t) { return std::hash<T>{}(t); },
+	}, value.data);
+
+	return hash_combine(value_hash, size_t(value.data.index()));
+}
diff --git a/musique/value/hash.hh b/musique/value/hash.hh
new file mode 100644
index 0000000..60f47f2
--- /dev/null
+++ b/musique/value/hash.hh
@@ -0,0 +1,17 @@
+#ifndef MUSIQUE_VALUE_HASH_HH
+#define MUSIQUE_VALUE_HASH_HH
+
+#include <functional>
+
+#define Hash_For(Name) \
+	struct Name; \
+	template<> \
+	struct std::hash<Name> { \
+		size_t operator()(Name const&) const noexcept; \
+	}; \
+
+Hash_For(Block)
+Hash_For(Set)
+Hash_For(Value)
+
+#endif // MUSIQUE_VALUE_HASH_HH
diff --git a/musique/value/set.cc b/musique/value/set.cc
new file mode 100644
index 0000000..d00a78e
--- /dev/null
+++ b/musique/value/set.cc
@@ -0,0 +1,60 @@
+#include <musique/value/value.hh>
+#include <musique/value/set.hh>
+
+
+Result<Value> Set::operator()(Interpreter&, std::vector<Value> params) const
+{
+	auto copy = *this;
+
+	if (auto a = match<Number>(params)) {
+		auto [length] = *a;
+		for (auto& value : copy.elements) {
+			if (auto chord = get_if<Chord>(value)) {
+				// FIXME This const_cast should be unnesesary
+				for (auto &note : const_cast<Chord*>(chord)->notes) {
+					note.length = length;
+				}
+				continue;
+			}
+		}
+	}
+
+	// TODO Error reporting when parameters doesnt match
+	// TODO reconsider different options for this data structure invocation
+	return copy;
+}
+
+Result<Value> Set::index(Interpreter&, unsigned position) const
+{
+	if (elements.size() < position) {
+		return errors::Out_Of_Range {
+			.required_index = position,
+			.size = elements.size()
+		};
+	}
+	// FIXME std::unordered_set::iterator has forward iterator, which means
+	// that any element lookup has complecity O(n). This may have serious
+	// performance implications and further investigation is needed.
+	return *std::next(elements.begin(), position);
+}
+
+usize Set::size() const
+{
+	return elements.size();
+}
+
+bool Set::is_collection() const
+{
+	return true;
+}
+
+std::strong_ordering Set::operator<=>(Set const&) const
+{
+	unimplemented();
+}
+
+std::ostream& operator<<(std::ostream& out, Set const& set)
+{
+	unimplemented();
+	return out;
+}
diff --git a/musique/value/set.hh b/musique/value/set.hh
new file mode 100644
index 0000000..610db76
--- /dev/null
+++ b/musique/value/set.hh
@@ -0,0 +1,36 @@
+#ifndef MUSIQUE_VALUE_SET_HH
+#define MUSIQUE_VALUE_SET_HH
+
+#include <unordered_set>
+#include <utility>
+
+// Needs to be always first, before all the implicit template instantiations
+#include <musique/value/hash.hh>
+
+#include <musique/value/collection.hh>
+#include <musique/value/function.hh>
+#include <musique/common.hh>
+
+struct Value;
+
+struct Set : Collection, Function
+{
+	std::unordered_set<Value> elements;
+
+	~Set() = default;
+
+	Result<Value> operator()(Interpreter &i, std::vector<Value> params) const override;
+
+	Result<Value> index(Interpreter &i, unsigned position) const override;
+
+	usize size() const override;
+
+	bool is_collection() const override;
+
+	bool operator==(Set const&) const = default;
+	std::strong_ordering operator<=>(Set const&) const;
+};
+
+std::ostream& operator<<(std::ostream& out, Set const& set);
+
+#endif
diff --git a/musique/value/value.cc b/musique/value/value.cc
index 8f12de2..a26971e 100644
--- a/musique/value/value.cc
+++ b/musique/value/value.cc
@@ -107,6 +107,11 @@ Value::Value(Chord chord)
 {
 }
 
+Value::Value(Set &&set)
+	: data(std::move(set))
+{
+}
+
 Result<Value> Value::operator()(Interpreter &i, std::vector<Value> args) const
 {
 	if (auto func = get_if<Function>(data)) {
@@ -188,7 +193,10 @@ std::ostream& operator<<(std::ostream& os, Value const& v)
 		[&](Nil)    { os << "nil"; },
 		[&](Intrinsic) { os << "<intrinisic>"; },
 		[&](Block const&) { os << "<block>"; },
-		[&](auto const& s) { os << s; }
+		[&](auto const& s) {
+			static_assert(requires { os << s; });
+			os << s;
+		}
 	}, v.data);
 	return os;
 }
@@ -205,6 +213,7 @@ std::string_view type_name(Value const& v)
 		[&](Nil const&)       { return "nil"; },
 		[&](Number const&)    { return "number"; },
 		[&](Symbol const&)    { return "symbol"; },
+		[&](Set const&)       { return "set"; },
 	}, v.data);
 }
 
@@ -228,28 +237,3 @@ Result<std::vector<Value>> flatten(Interpreter &i, std::vector<Value> args)
 	return flatten(i, std::span(args));
 }
 
-std::size_t std::hash<Value>::operator()(Value const& value) const
-{
-	auto const value_hash = std::visit(Overloaded {
-		[](Nil) { return std::size_t(0); },
-		[](Intrinsic i) { return size_t(i.function_pointer); },
-		[](Block const& b) { return hash_combine(std::hash<Ast>{}(b.body), b.parameters.size()); },
-		[this](Array const& array) {
-			return std::accumulate(
-				array.elements.begin(), array.elements.end(), size_t(0),
-				[this](size_t h, Value const& v) { return hash_combine(h, operator()(v)); }
-			);
-		},
-		[](Chord const& chord) {
-			return std::accumulate(chord.notes.begin(), chord.notes.end(), size_t(0), [](size_t h, Note const& n) {
-				h = hash_combine(h, std::hash<std::optional<int>>{}(n.base));
-				h = hash_combine(h, std::hash<std::optional<Number>>{}(n.length));
-				h = hash_combine(h, std::hash<std::optional<i8>>{}(n.octave));
-				return h;
-			});
-		},
-		[]<typename T>(T const& t) { return std::hash<T>{}(t); },
-	}, value.data);
-
-	return hash_combine(value_hash, size_t(value.data.index()));
-}
diff --git a/musique/value/value.hh b/musique/value/value.hh
index 21d3fc3..8255b87 100644
--- a/musique/value/value.hh
+++ b/musique/value/value.hh
@@ -1,6 +1,9 @@
 #ifndef MUSIQUE_VALUE_HH
 #define MUSIQUE_VALUE_HH
 
+// Needs to be always first, before all the implicit template instantiations
+#include <musique/value/hash.hh>
+
 #include <musique/accessors.hh>
 #include <musique/common.hh>
 #include <musique/lexer/token.hh>
@@ -10,6 +13,7 @@
 #include <musique/value/chord.hh>
 #include <musique/value/intrinsic.hh>
 #include <musique/value/note.hh>
+#include <musique/value/set.hh>
 
 struct Nil
 {
@@ -40,6 +44,7 @@ struct Value
 	Value(char const* s);              ///< Create value of type symbol holding provided symbol
 	Value(std::string s);              ///< Create value of type symbol holding provided symbol
 	Value(std::string_view s);         ///< Create value of type symbol holding provided symbol
+	Value(Set &&set);                  ///< Create value of type set holding provided set
 	explicit Value(std::vector<Value> &&array); ///< Create value of type array holding provided array
 
 	// TODO Most strings should not be allocated by Value, but reference to string allocated previously
@@ -54,6 +59,7 @@ struct Value
 		Intrinsic,
 		Block,
 		Array,
+		Set,
 		Chord,
 		Macro
 	> data = Nil{};
@@ -108,9 +114,6 @@ inline T* get_if(Value& v) { return get_if<T>(v.data); }
 /// Returns type name of Value type
 std::string_view type_name(Value const& v);
 
-std::ostream& operator<<(std::ostream& os, Value const& v);
-template<> struct std::hash<Value>  { std::size_t operator()(Value  const&) const; };
-
 template<typename T>
 Result<Value> wrap_value(Result<T> &&value)
 {
@@ -170,4 +173,6 @@ constexpr auto match(Values& ...values) -> std::optional<std::tuple<T&...>>
 	} (std::make_index_sequence<sizeof...(T)>{});
 }
 
+std::ostream& operator<<(std::ostream& os, Value const& v);
+
 #endif