# launch\_exchange

An entrypoint that launches a new exchanges. Next types of exchanges are supported:

* FA1.2/FA1.2;
* FA1.2/FA2;
* FA1.2/TEZ;
* FA2/FA1.2;
* FA2/FA2;
* FA2/TEZ;
* TEZ/FA1.2;
* TEZ/FA2.

In case of TOK/TEZ exchange launch [voting](/smart-contracts/dex-2.0/bucket-contract/entrypoints-overview/vote.md) in appropriative [Bucket](/smart-contracts/dex-2.0/bucket-contract.md) contract is executed. Also all TEZ tokens is [transferred](/smart-contracts/dex-2.0/bucket-contract/entrypoints-overview/fill.md) to the same [Bucket](/smart-contracts/dex-2.0/bucket-contract.md) contract before voting.

In time of first exchange launch, this contract calls [***launch\_callback***](/smart-contracts/dex-2.0/dexcore-contract/entrypoints-overview/callbacks/launch_callback.md) entrypoint. This is done in order to vote on a [Bucket](/smart-contracts/dex-2.0/bucket-contract.md) contract that has just been deployed and cannot be accessed until the launch exchange transaction completes. Therefore, voting takes place in the next transaction, sent from [***launch\_callback***](/smart-contracts/dex-2.0/dexcore-contract/entrypoints-overview/callbacks/launch_callback.md).

### Call parameters

```pascaligo
type tez_t              is unit

type fa12_token_t       is address

type fa2_token_t        is [@layout:comb] record [
  token                   : address;
  id                      : nat;
]

type token_t            is
| Tez                     of tez_t
| Fa12                    of fa12_token_t
| Fa2                     of fa2_token_t

type tokens_t           is [@layout:comb] record [
  token_a                 : token_t;
  token_b                 : token_t;
]

type launch_exchange_t  is [@layout:comb] record [
  pair                    : tokens_t;
  token_a_in              : nat;
  token_b_in              : nat;
  shares_receiver         : address;
  candidate               : key_hash;
  deadline                : timestamp;
]
```

#### tokens\_t

| Field    | Type     | Description         |
| -------- | -------- | ------------------- |
| token\_a | token\_t | FA1.2/FA2/TEZ token |
| token\_b | token\_t | FA1.2/FA2/TEZ token |

#### launch\_exchange\_t

<table><thead><tr><th>Field</th><th width="150">Type</th><th>Description</th></tr></thead><tbody><tr><td>pair</td><td><a href="#tokens_t">tokens_t</a></td><td>Tokens to launch exchange with</td></tr><tr><td>token_a_in</td><td>nat</td><td>Amount of token A for investment</td></tr><tr><td>token_b_in</td><td>nat</td><td>Amount of token B for investment</td></tr><tr><td>shares_receiver</td><td>address</td><td>Receiver of LP tokens</td></tr><tr><td>candidate</td><td>key_hash</td><td>Baker for voting (is used only in case of TOK/TEZ exchanges launch). Ignored otherwise</td></tr><tr><td>deadline</td><td>timestamp</td><td>The time until which the transaction remains valid and will not be rejected</td></tr></tbody></table>

### Usage

{% hint style="danger" %}
Note: you need to pass positive TEZ/mutez amount to the ***send()*** method in case of FA1.2/TEZ or FA2/TEZ exchanges launch (see example below).

Also don't forget to add the [DexCore](/smart-contracts/dex-2.0/dexcore-contract.md) contract as the operator for your FA2 tokens or make an approve for spending of FA1.2 tokens in time of exchange launch.
{% endhint %}

{% tabs %}
{% tab title="🌮 Taquito" %}

```javascript
const dexCoreAddress = "KT1...";
const params = {
    pair: {
        token_a: {
            fa12: "KT1...",
        }, 
        token_b: {
            tez: undefined,
        },
    },
    token_a_in: 100,
    token_b_in: 100,
    shares_receiver: "tz1.../KT1...",
    candidate: "tz1...",
    deadline: String(Date.parse((await tezos.rpc.getBlockHeader()).timestamp) / 1000 + 100),
};
const dexCore = await tezos.contract.at(dexCoreAddress);
const operation = await dexCore.methodsObject.launch_exchange(params).send({ amount: params.token_b_in, mutez: true });

await operation.confirmation();
```

{% endtab %}
{% endtabs %}

{% hint style="info" %}
Pass `candidate: "tz1ZZZZZZZZZZZZZZZZZZZZZZZZZZZZNkiRg"`in case of launching TOK/TOK exchange
{% endhint %}

### Errors

* `104` - wrong order of a tokens from parameters.
* `105` - zero token A amount in.
* `106` - zero token B amount in.
* `107` - pair (pool) with the specified `token_id` already listed.
* `120` - wrong TEZ amount were passed to the transaction.
* `136` - reentrancy.
* `144` - action outdated (the time until which the transaction remained valid was passed).
* `412` - non payable entrypoint (can't accept TEZ tokens during call of an entrypoint). Only in case of launching of TOK/TOK liquidity pools (pairs).


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