Entries, Functions

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Entries, Functions
A contract is operated through entry points.
Entry point
The keyword entry is used to declare an entry point followed by its name.
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entry main() {
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  ...
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}
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If the required entry point name conflicts with a language keyword, you may prefix the id with % to bypass these constraints. For example, transfer is a the identifier reserved for the transfer instruction.  The following enables us to declare an entry point named transfer.
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entry %transfer () {
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   ...
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}
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Arguments
An entry may take arguments. For example, the entry below named "complete" takes two arguments value and amount , respectively of type string and int:
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entry complete (value : string, amount : int) {
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​
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  ...  
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​
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}
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Sections
An entry is made of sections listed below:
name
description
optional
called by
specifies which role(s) may call the action
yes
refuse transfer
specifies whether the action refuses incoming 
currency transfer (accepted by default).
yes
require
lists the required condition to pass in order to 
execute the action. 
yes
specification
specifies formal properties the action effect has
 (see "specification" section)
yes
effect
codes the effect of the action:
changes in data storage
transfers of currencies 
yes
For example, the complete entry example may be enhanced as follows:
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constant owner : role = @tz1KksC8RvjUWAbXYJuNrUbontHGor25Cztk
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​
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variable threshold : tez = 10tz
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​
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action complete (value : string, amount : int) {
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  called by owner
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  require {
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    r : transferred > threshold
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  }
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  effect {
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    ... 
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  }
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}
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transferred is the amount of tez transferred to the entry.
In the expression line 9 above, r is a label for the require expression (see Label section below).
Label
In Archetype, some expressions are named. The following syntax is used to name an expression:
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lbl : ... expression ... /* lbl is a label */
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The following is the list of expressions that require a label:
Type
Example
Require
require {
  r1 otherwise "NotEnoughTransferred" : transferred > threshold
}
Fail if
failif {
  f1 with "NotEnoughTransferred" : transferred <= threshold
}
Asset invariant
asset mile {
  quantity : int
} with {
  quant_strictly_pos : quantity > 0
}
(see Contract specification)
Security predicate
security {
  s1 : only_by_role(anyaction, admin)
}
(see Contract specification)
Effect
Local variable 
A local variable is declared as exampled below:
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var p = amount + 10tz;
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Data assignment
A variable (global or local) is assigned a new value as exampled below:
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p := amount;
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Note that is it not possible to assign a value to an input value.
Conditional
The basic conditional expression is exampled below :
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if transferred > threshold then (
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  transfer price to owner;
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  transfer 1tz to coder
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) else
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  fail("not enough");
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Failing
The fail instruction interrupts the execution. It reverts the contract storage to its initial state.
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fail("Error");
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The dorequire expression fails if the condition is not met:
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dorequire (balance > threshold,"NotEnoughBalance")
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The dofailif expression fails if the condition is met:
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dofailif (balance <= threshold, "NotEnoughBalance")
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It is possible to pass any Michelson-compliant typed value as the error message of the fail instructions above. 
For example, the following passes the balance and the threshold as additional error message information:
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dofailif (balance <= threshold, ("NotEnoughBalance",(balance,threshold)))
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Function
It is possible to declare functions with the function keyword. The main differences between entries and functions are:
functions return a value with the return keyword
functions cannot modify the contract's storage (they are "pure")
Typically functions help factorize computation codes.
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function get_rate (amount : tez) : rational {
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   var a : nat  = amount;
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   return (a / 3600)
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}
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Functions are called with the standard call syntax:
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effect {
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   var r = get_rate(transferred);
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   if r < 3.14125 then fail("invalid transferred amount");
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}
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Crypto
Transfers, contract calls
Last modified 8mo ago
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