Entry point

The keyword entry is used to declare an entry point followed by its name.

entry main() {
  ...
}

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.

entry %transfer () {
   ...
}

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:

entry complete (value : string, amount : int) {
​
  ...  
​
}

Sections

An entry is made of sections listed below:

For example, the complete entry example may be enhanced as follows:

constant owner : role = @tz1KksC8RvjUWAbXYJuNrUbontHGor25Cztk
​
variable threshold : tez = 10tz
​
action complete (value : string, amount : int) {
  called by owner
  
  require {
    r : transferred > threshold
  }
  
  effect {
    ... 
  }
}

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:

lbl : ... expression ... /* lbl is a label */

The following is the list of expressions that require a label:

Effect

Local variable

A local variable is declared as exampled below:

var p = amount + 10tz;

Data assignment

A variable (global or local) is assigned a new value as exampled below:

p := amount;

Note that is it not possible to assign a value to an input value.

Conditional

The basic conditional expression is exampled below :

if transferred > threshold then (
  transfer price to owner;
  transfer 1tz to coder
) else
  fail("not enough");

Failing

The fail instruction interrupts the execution. It reverts the contract storage to its initial state.

fail("Error");

The dorequire expression fails if the condition is not met:

dorequire (balance > threshold,"NotEnoughBalance")

The dofailif expression fails if the condition is met:

dofailif (balance <= threshold, "NotEnoughBalance")

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:

dofailif (balance <= threshold, ("NotEnoughBalance",(balance,threshold)))

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.

function get_rate (amount : tez) : rational {
   var a : nat  = amount;
   return (a / 3600)
}

Functions are called with the standard call syntax:

effect {
   var r = get_rate(transferred);
   if r < 3.14125 then fail("invalid transferred amount");
}