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change contract-send-tx to as-contract. add example usage.

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Aaron Blankstein
2018-12-06 19:20:33 -06:00
parent a0926def2e
commit c1e813c085
1 changed files with 29 additions and 6 deletions
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35
sip/sip-002-smart-contract-language.md
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@@ -143,20 +143,43 @@ principal can operate on their assets by issuing a signed transaction
on the blockchain. _Smart contracts_ may also be principals
(reprepresented by the smart contract's identifier), however, there is
no private key associated with the smart contract, and it cannot
broadcast a signed transaction on the blockchain. In order to allow
smart contracts to authorize transactions with the smart contract's
own principal, smart contracts may use the special function:
broadcast a signed transaction on the blockchain.
In order to allow smart contracts to authorize transactions with the
smart contract's own principal, smart contracts may use the special
function:
```scheme
(contract-send-tx (...))
(as-contract (...))
```
This function will execute the commands passed as an argument with the
This function will execute the closure (passed as an argument) with the
`tx-sender` set to the _contract's_ principal, rather than the current
sender. It returns the return value of the provided commands. A smart
sender. It returns the return value of the provided closure. A smart
contract may use the special variable `contract-principal` to refer to
its own principal.
For example, a smart contract that implements something like a "token
faucet" could be implemented as so:
```scheme
(deftx (claim-from-faucet)
(if (isnull? (fetch-entry claimed-before (tuple #sender tx-sender)))
(let ((requester tx-sender)) ;; set a local variable requester = tx-sender
(insert-entry! claimed-before (tuple #sender requester) (tuple #claimed 'true))
(as-contract (stacks-transfer! requester 1)))))
```
Here, the transaction `claim-from-faucet`:
1. Checks if the sender has claimed from the faucet before
2. Assigns the tx sender to a requester variable
3. Adds an entry to the tracking map
4. Uses `as-contract` to send 1 microstack
The primitive function `is-contract?` can be used to determine
whether a given principal corresponds to a smart contract.
## Stacks Transaction Primitives
To interact with Stacks balances, smart contracts may call the