Token Swap Program

This example demonstrates a simple token swap program whereby two parties wish to exchange specific amounts of (different) tokens they each hold, at a rate they have previously agreed on. The program ensures the swap happens atomically, so neither party can withdraw without completing the trade.

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title: Valence token swap program
---
graph LR
	InA((Party A Deposit))
	InB((Party B Deposit))
	OutA((Party A Withdraw))
	OutB((Party B Withdraw))
	SSA[Splitter A]
	SSB[Splitter B]
	subgraph Neutron
	InA --> SSA --> OutB
	InB --> SSB --> OutA
	end

The program is composed of the following components:

• Party A Deposit account: a Valence account which Party A will deposit their tokens into, to be exchanged with Party B's tokens.
• Splitter A: an instance of the Splitter library that will transfer Party A's tokens from its input account (i.e. the Party A Deposit account) to its output account (i.e. the Party B Withdraw account) upon execution of its split function.
• Party B Withdraw account: the account from which Party B can withdraw Party A's tokens after the swap has successfully completed. Note: this can be a Valence account, but it could also be a regular chain account, or a smart contract.
• Party B Deposit account: a Valence account which Party B will deposit their funds into, to be exchanged with Party A's funds.
• Splitter B: an instance of the Splitter library that will transfer Party B's tokens from its input account (i.e. the Party B Deposit account) to its output account (i.e. the Party A Withdraw account) upon execution of its split function.
• Party A Withdraw account: the account from which Party A can withdraw Party B's tokens after the swap has successfully completed. Note: this can be a Valence account, but it could also be a regular chain account, or a smart contract.

The way the program is able to fulfil the requirement for an atomic exchange of tokens between the two parties is done by implementing an atomic subroutine composed of two function calls:

1. Splitter A's split function
2. Splitter B's split function

The Authorizations component will ensure that either both succeed, or none is executed, thereby ensuring that funds remain safe at all time (either remaining in the respective deposit accounts, or transferred to the respective withdraw accounts).