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Checking the tutorial 

Signed-off-by: Mary Anthony <mary@blockstack.com>
feat/clarity-updates
Mary Anthony 5 years ago
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      _core/smart/tutorial.md

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_core/smart/tutorial.md
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@ -62,35 +62,36 @@ Blockstack publishes the `clarity-developer-preview` image on Docker hub. A cont
If you haven't already done so, use the `cat` or `more` command to display the `tokens.clar` file's code. Clarity is designed for static analysis; it is not a compiled language and is not Turing complete. It language is a LISP-like language. LISP is an acronym for list processing. If you haven't already done so, use the `cat` or `more` command to display the `tokens.clar` file's code. Clarity is designed for static analysis; it is not a compiled language and is not Turing complete. It language is a LISP-like language. LISP is an acronym for list processing.
The first line of the `tokens.clar` program contains a user-defined `get-balance` function. The first lines of the `tokens.clar` program contains a user-defined `get-balance` function.
```cl ```cl
(define (get-balance (account principal)) (define-map tokens ((account principal)) ((balance int)))
(default-to 0 (get balance (fetch-entry tokens (tuple (account account)))))) (define-private (get-balance (account principal))
(default-to 0 (get balance (map-get tokens (tuple (account account))))))
``` ```
`get-balance` is a private function because it is constructed with the `define` call. To create public functions, you would use the `define-public` function. Public functions can be called from other contracts or even from the command line with the `clarity-cli`. `get-balance` is a private function because it is constructed with the `define-private` call. To create public functions, you would use the `define-public` function. Public functions can be called from other contracts or even from the command line with the `clarity-cli`.
Notice the program is enclosed in `()` (parentheses) and each statement as well. The `get-balance` function takes an `account` argument of the special type `principal`. Principals represent a spending entity and are roughly equivalent to a Stacks address. Notice the program is enclosed in `()` (parentheses) and each statement as well. The `get-balance` function takes an `account` argument of the special type `principal`. Principals represent a spending entity and are roughly equivalent to a Stacks address.
Along with the `principal` types, Clarity supports booleans, integers, and fixed length buffers. Variables are created via `let` binding but there is no support for mutating functions like `set`. Along with the `principal` types, Clarity supports booleans, integers, and fixed length buffers. Variables are created via `let` binding but there is no support for mutating functions like `set`.
The next sequence of lines shows an `if` statement that allows you to set conditions for execution in the language.. The next sequence of lines shows an `if` statement that allows you to set conditions for execution in the language.
```cl ```cl
(define (token-credit! (account principal) (tokens int)) (define-private (token-credit! (account principal) (amount int))
(if (<= tokens 0) (if (<= amount 0)
(err "must move positive balance") (err "must move positive balance")
(let ((current-amount (get-balance account))) (let ((current-amount (get-balance account)))
(begin (begin
(set-entry! tokens (tuple (account account)) (map-set! tokens (tuple (account account))
(tuple (balance (+ tokens current-amount)))) (tuple (balance (+ amount current-amount))))
(ok tokens))))) (ok amount)))))
``` ```
Every smart contract has both a data space and code. The data space of a contract may only interact with that contract. This particular function is interacting with a map named `tokens`. The `set-entry!` function is a native function that sets the value associated with the input key to the inputted value in the `tokens` data map. Because `set-entry!` mutates data so it has an `!` exclamation point; this is by convention in Clarity. Every smart contract has both a data space and code. The data space of a contract may only interact with that contract. This particular function is interacting with a map named `tokens`. The `set-entry!` function is a native function that sets the value associated with the input key to the inputted value in the `tokens` data map. Because `set-entry!` mutates data so it has an `!` exclamation point; this is by convention in Clarity.
In the first `token-transfer` public function, you see that it calls the private `get-balance` function and passes it `tx-sender`. The `tx-sender` isa a globally defined variable that represents the the current principal. In the first `token-transfer` public function, you see that it calls the private `get-balance` function and passes it `tx-sender`. The `tx-sender` is a globally defined variable that represents the the current principal.
```cl ```cl
(define-public (token-transfer (to principal) (amount int)) (define-public (token-transfer (to principal) (amount int))
@ -98,7 +99,7 @@ In the first `token-transfer` public function, you see that it calls the private
(if (or (> amount balance) (<= amount 0)) (if (or (> amount balance) (<= amount 0))
(err "must transfer positive balance and possess funds") (err "must transfer positive balance and possess funds")
(begin (begin
(set-entry! tokens (tuple (account tx-sender)) (map-set! tokens (tuple (account tx-sender))
(tuple (balance (- balance amount)))) (tuple (balance (- balance amount))))
(token-credit! to amount))))) (token-credit! to amount)))))
@ -114,10 +115,10 @@ The final two lines of the program pass a principal, represented by a Stacks add
Smart contracts may call other smart contracts using a `contract-call!` function. This means that if a transaction invokes a function in a given smart contract, that function is able to make calls into other smart contracts on your behalf. The ability to read and do a static analysis of Clarity code allows clients to learn which functions a given smart contract will ever call. Good clients should always warn users about any potential side effects of a given transaction. Smart contracts may call other smart contracts using a `contract-call!` function. This means that if a transaction invokes a function in a given smart contract, that function is able to make calls into other smart contracts on your behalf. The ability to read and do a static analysis of Clarity code allows clients to learn which functions a given smart contract will ever call. Good clients should always warn users about any potential side effects of a given transaction.
Take a moment to `cat` the contents of the `names.clar` file. Take a moment to `cat` the contents of the `sample-programs/names.clar` file.
```bash ```bash
cat names.clar cat sample-programs/names.clar
```` ````
Which `tokens.clar` function is being called? Which `tokens.clar` function is being called?
@ -140,11 +141,11 @@ In this task, you interact with the the contracts using the `clarity-cli` comman
```bash ```bash
# clarity-cli check sample-programs/names.clar /data/db # clarity-cli check sample-programs/names.clar /data/db
``` ```
You should get an error: You should get an error:
``` ```
Type check error. Error (line 11, column 1): use of unresolved contract ''S1G2081040G2081040G2081040G208105NK8PE5.tokens'.
NoSuchContract("tokens")
``` ```
This happens because the `names.clar` contract _calls_ the `tokens.clar` contract, and that contract has not been created on the blockchain. This happens because the `names.clar` contract _calls_ the `tokens.clar` contract, and that contract has not been created on the blockchain.

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