---
id: tezos-specific
title: Tezos Domain-Specific Operations
---
import Syntax from '@theme/Syntax';
LIGO is a programming language for writing Tezos smart contracts. It
would be a little odd if it did not have any Tezos specific
functions. This page will tell you about them.
## Pack and Unpack
As Michelson provides the `PACK` and `UNPACK` instructions for data
serialization, so does LIGO with `Bytes.pack` and `Bytes.unpack`. The
former serializes Michelson data structures into a binary format, and
the latter reverses that transformation. Unpacking may fail, so the
return type of `Byte.unpack` is an option that needs to be annotated.
> ⚠️ `PACK` and `UNPACK` are Michelson instructions that are intended
> to be used by people that really know what they are doing. There are
> several risks and failure cases, such as unpacking a lambda from an
> untrusted source or casting the result to the wrong type. Do not use
> the corresponding LIGO functions without doing your homework first.
<Syntax syntax="pascaligo">
```pascaligo group=a
function id_string (const p : string) : option (string) is block {
const packed : bytes = Bytes.pack (p)
} with (Bytes.unpack (packed) : option (string))
```
> Note that `bytes_pack` and `bytes_unpack` are *deprecated*.
</Syntax>
<Syntax syntax="cameligo">
```cameligo group=a
let id_string (p : string) : string option =
let packed: bytes = Bytes.pack p in
(Bytes.unpack packed : string option)
```
</Syntax>
<Syntax syntax="reasonligo">
```reasonligo group=a
let id_string = (p : string) : option (string) => {
let packed : bytes = Bytes.pack (p);
(Bytes.unpack(packed) : option (string));
};
```
</Syntax>
## Hashing Keys
It is often desirable to hash a public key. In Michelson, certain data
structures such as maps will not allow the use of the `key` type. Even
if this were not the case, hashes are much smaller than keys, and
storage on blockchains comes at a cost premium. You can hash keys with
a predefined functions returning a value of type `key_hash`.
<Syntax syntax="pascaligo">
```pascaligo group=b
function check_hash_key (const kh1 : key_hash; const k2 : key) : bool * key_hash is
block {
var ret : bool := False;
var kh2 : key_hash := Crypto.hash_key (k2);
if kh1 = kh2 then ret := True else skip
} with (ret, kh2)
```
> Note that `hash_key` is *deprecated*. Please use `Crypto.hash_key`.
</Syntax>
<Syntax syntax="cameligo">
```cameligo group=b
let check_hash_key (kh1, k2 : key_hash * key) : bool * key_hash =
let kh2 : key_hash = Crypto.hash_key k2 in
(kh1 = kh2), kh2
```
</Syntax>
<Syntax syntax="reasonligo">
```reasonligo group=b
let check_hash_key = ((kh1, k2) : (key_hash, key)) : (bool, key_hash) => {
let kh2 : key_hash = Crypto.hash_key (k2);
((kh1 == kh2), kh2);
};
```
</Syntax>
## Checking Signatures
Sometimes a contract will want to check that a message has been signed
by a particular key. For example, a point-of-sale system might want a
customer to sign a transaction so it can be processed
asynchronously. You can do this in LIGO using the `key` and
`signature` types.
> ⚠️ There is no way to *generate* a signed message in LIGO. This is
> because that would require storing a private key on chain, at which
> point it is not... private anymore.
<Syntax syntax="pascaligo">
```pascaligo group=c
function check_signature
(const pk : key;
const signed : signature;
const msg : bytes) : bool
is Crypto.check (pk, signed, msg)
```
> Note that `crypto_check` is *deprecated*.
</Syntax>
<Syntax syntax="cameligo">
```cameligo group=c
let check_signature (pk, signed, msg : key * signature * bytes) : bool =
Crypto.check pk signed msg
```
</Syntax>
<Syntax syntax="reasonligo">
```reasonligo group=c
let check_signature =
((pk, signed, msg) : (key, signature, bytes)) : bool =>
Crypto.check (pk, signed, msg);
```
</Syntax>
## Contract's Own Address
Often you want to get the address of the contract being executed. You
can do it with `Tezos.self_address`.
> Note that `self_address` is *deprecated*.
> ⚠️ Due to limitations in Michelson, `Tezos.self_address` in a
> contract is only allowed at the top-level. Using it in an embedded
> function will cause an error.
<Syntax syntax="pascaligo">
```pascaligo group=d
const current_addr : address = Tezos.self_address
```
</Syntax>
<Syntax syntax="cameligo">
```cameligo group=d
let current_addr : address = Tezos.self_address
```
</Syntax>
<Syntax syntax="reasonligo">
```reasonligo group=d
let current_addr : address = Tezos.self_address;
```
</Syntax>
## Origination of a contract
`Tezos.create_contract` allows you to originate a contract given its code, delegate (if any), initial balance and initial storage.
The return value is a pair of type `(operation * address)`.
> ⚠️ Due to limitations in Michelson, `Tezos.create_contract` first argument
> must be inlined and must not contain references to free variables
<Syntax syntax="pascaligo">
```pascaligo group=e
const origination : operation * address = Tezos.create_contract (
function (const p : nat; const s : string): list(operation) * string is ((nil : list(operation)), s),
(None : option(key_hash)),
3tz,
"initial_storage")
```
</Syntax>
<Syntax syntax="cameligo">
```cameligo group=e
let origination : operation * address = Tezos.create_contract
(fun (p, s : nat * string) -> (([] : operation list), s))
(None: key_hash option)
3tz
"initial_storage"
```
</Syntax>
<Syntax syntax="reasonligo">
```reasonligo group=e
let origination : (operation, address) = Tezos.create_contract (
((p, s) : (nat,string)) : (list(operation),string) => (([] : list(operation)), s),
None: option(key_hash),
3tz,
"initial_storage")
```
</Syntax>