---
id: types
title: Types
---

LIGO is strongly and statically typed. This means that the compiler checks your program at compilation time and makes sure there won't be any type related runtime errors. LIGO types are built on top of Michelson's type system.

## Built-in types

For quick referrence, you can find all the built-in types [here](https://gitlab.com/ligolang/ligo/blob/dev/src/passes/operators/operators.ml#L35).

## Type aliases

Type aliasing is great for creating a readable / maintainable smart contract. One well typed type/variable is worth a thousand words. For example we can choose to *alias* a string as an animal breed - this will allow us to comunicate our intent with added clarity.

<!--DOCUSAURUS_CODE_TABS-->
<!--Pascaligo-->
```pascaligo
type animalBreed is string;
const dogBreed : animalBreed = "Saluki";
```

<!--Cameligo-->

```cameligo
type animal_breed = string
let dog_breed: animal_breed = "Saluki"
```

<!--Reasonligo-->

```reasonligo
type animal_breed = string;
let dog_breed: animal_breed = "Saluki";
```

<!--END_DOCUSAURUS_CODE_TABS-->

## Simple types
<!--DOCUSAURUS_CODE_TABS-->
<!--Pascaligo-->
```pascaligo
// accountBalances is a simple type, a map of address <-> tez
type accountBalances is map(address, tez);

const ledger: accountBalances = map
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address) -> 10mutez
end
```

<!--Cameligo-->
```cameligo
// account_balances is a simple type, a map of address <-> tez
type account_balances = (address, tez) map

let ledger: account_balances = Map.literal
  [(("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address), 10mutez)]
```

<!--Reasonligo-->
```reasonligo
// account_balances is a simple type, a map of address <-> tez
type account_balances = map(address, tez);

let ledger: account_balances =
  Map.literal([
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address, 10(mutez)),
  ]);
```

<!--END_DOCUSAURUS_CODE_TABS-->

## Composed types

Often contracts require complex data structures, which in turn require well-typed storage or functions to work with. LIGO offers a simple way to compose simple types into larger & more expressive composed types.

In the example below you can see the definition of data types for a ledger that keeps the balance and number of previous transactions for a given account.

<!--DOCUSAURUS_CODE_TABS-->
<!--Pascaligo-->
```pascaligo
// alias two types
type account is address;
type numberOfTransactions is nat;
// accountData consists of a record with two fields (balance, numberOfTransactions)
type accountData is record
    balance: tez;
    numberOfTransactions: numberOfTransactions;
end
// our ledger / accountBalances is a map of account <-> accountData
type accountBalances is map(account, accountData);

// pseudo-JSON representation of our map
// { "tz1...": {balance: 10mutez, numberOfTransactions: 5n} }
const ledger: accountBalances = map
    ("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address) -> record
      balance = 10mutez;
      numberOfTransactions = 5n;
    end
end
```

<!--Cameligo-->
```cameligo
(* alias two types *)
type account = address
type number_of_transactions = nat
(* account_data consists of a record with two fields (balance, number_of_transactions) *)
type account_data = {
 balance: tez;
 number_of_transactions: number_of_transactions;
}
(* our ledger / account_balances is a map of account <-> account_data *)
type account_balances = (account, account_data) map

// pseudo-JSON representation of our map
// {"tz1...": {balance: 10mutez, number_of_transactions: 5n}}
let ledger: account_balances = Map.literal
  [(("tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address),
    {balance = 10mutez;
     number_of_transactions = 5n;}
   )]
```

<!--Reasonligo-->
```reasonligo
/* alias two types */
type account = address;
type number_of_transactions = nat;
/* account_data consists of a record with two fields (balance, number_of_transactions) */
type account_data = {
  balance: tez,
  number_of_transactions,
};
/* our ledger / account_balances is a map of account <-> account_data */
type account_balances = map(account, account_data);

// pseudo-JSON representation of our map
// {"tz1...": {balance: 10mutez, number_of_transactions: 5n}}
let ledger: account_balances =
  Map.literal([
    (
      "tz1KqTpEZ7Yob7QbPE4Hy4Wo8fHG8LhKxZSx": address,
      {balance: 10(mutez), number_of_transactions: 5n},
    ),
  ]);

```

<!--END_DOCUSAURUS_CODE_TABS-->
