Smart contracts have the potential to automate business processes and create logic that can be executed without human interaction. This can be useful for minimizing trust and creating truly decentralized applications.
In Iroha v1 a finite set of commands was provided, but they were inflexible and Turing complete computation was not possible. To increase the usefulness of Iroha, in v2 we allow full, Turing complete computation, while still making common tasks easy by providing Iroha Special Instructions (ISI).
https://github.com/hyperledger/iroha/blob/iroha2-dev/iroha_2_whitepaper.md
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