> For the complete documentation index, see [llms.txt](https://learn.fi-code.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://learn.fi-code.com/overview/types.md). # Basic Types fi is a statically typed language, where a variable must be typed on declaration and that type cannot change. When you are setting a variable to a literal value, you must also ensure the type is declared. ``` storage nat Foo; entry Test(int Bar){ let string Hello = string "World"; #We must declare the type of all literals } ``` During compilation, types are strictly checked and enforced. These types reflect the native Michelson types. All available basic types are defined below: ## Boolean **bool** - possible values being either **true** or **false**. ``` let bool available = bool true; ``` ## Integers & Natural Numbers Integers and naturals are arbitrary-precision, meaning the only size limit is fuel. The only difference is that Natural Numbers are unsigned. **int** - possible values being any integer value (negative and positive)\ **nat** - possible values being any positive integer value ``` let nat n1 = nat 1; let nat n2 = nat 2; let nat n3 = sub(n1, n2); # Fail - must be declared as an int let int n4 = sub(n1, n2); # OK let nat n5 = to_int(sub(n1, n2)); # Also OK ``` **Note: Some arithmetic functions will return a different type based on the input types. You can use to\_\* functions if you need to typecast a specific value.** ## Strings Strings are used to hold a value in text form. **string** - possible value being anything, but must be encompassed by double-quotes **"text"** ``` let string name = string "John"; ``` ## Mutez Mutez is the native Michelson type for defining a variable to represent a mutez, the native currency of Tezos in its smallest denomination (e.g. 0.000001 tez). > Mutez are internally represented by a 64 bit signed integer. There are restrictions to prevent creating a negative amount of mutez. Operations are limited to prevent overflow and mixing them with other numerical types by mistake. They are also checked for under/overflows. **mutez** - possible values being any positive integer value ``` let mutez amount = mutez 100000000; ``` ## Timestamp Timestamps represent a date/time value. **timestamp** - valid RFC 339 notation, encompassed by double-quotes, or alternatively number of seconds since Unix Epoch. ``` let timestamp today = timestamp "2019-02-20 00:00:00"; let timestamp alsotoday = timestamp 1550638795; ``` ## Address Addresses are untyped native contract addresses stored on the Tezos blockchain. **address** - must be a valid public address and must be provided in the base58-check encoded version encompassed by double quotes (e.g. "KT1...", "tz1..."). ``` let address payee = address "tz1..."; ``` ## Public Key Public keys are used for verifying a signed message using the verify function, or can be converted to a public key hash (pkh/key\_hash) and used for on-chain operations (delegation, origination and transfer). **key** - must be a valid public key, encompassed by double quotes, in the base58-check encoded format (e.g. "edpk...", "p2pk") ``` let key signer = key "edpk..."; ``` ## Public Key Hash Public key hashes are the hashed form of a key, and can also be used to create an implicit contract (and therefore address using typecasting). This type can be declared as key\_hash or via an alias, pkh. **key\_hash|pkh** - must be a valid public key hash, encompassed by double quotes, in the base58-check encoded format (e.g. "tz1...", "tz2..."). ``` let key_hash signer = pkh "tz1..."; ``` ## Signature Signatures are base58-check encoded signatures (e.g. "edsig..."). These can be generated by the node-client to sign a message with a users private key. This can then be verified within fi using the verify function. **signature** - must be a valid base58-check encoded signature, encompassed by double-quotes "..." ``` let signature sig = signature "edsig..."; ``` ## Bytes Bytes are defined as hexadecimal, and can be used for multiple purposes. **bytes** - must be valid hex, starting with 0x. This should not be wrapped in double quotes; ``` let bytes b = bytes 0x08aa28; ``` --- # Agent Instructions This documentation is published with GitBook. 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