Exceptions

In some cases it is necessary to interrupt the flow of execution with a failure: this is where the predefined function failwith comes in.

The failwith function

The failwith function raises an error that cannot be caught, which terminates the contract.

let main = (p: unit, s: unit): unit => {

if (true) {

failwith("This contract always fails");

};

}

The call to failwith should be annotated with a type as the type-checker cannot infer the correct type yet.

Assertions

Assertions can be used to ensure a certain condition is met when running a contract. The predefined function assert is used to check whether a given a Boolean condition is true. The function assert_some is used to check if an option value is not None. The function assert_some_with_error is like assert_some but an error message can be given. When a condition is not met, the contract will stop executing and display an error.

let main = (p: bool, s: unit): [list<operation>, unit] => {

let u: unit = assert(p);

return [list([]) as list<operation>, s];

};

let some = (o: option<unit>): unit => {

assert_some(o)

};

You can use assert_with_error or assert_some_with_error to use a custom error message

let main2 = (p: bool, s: unit): [list<operation>, unit] => {

let u: unit = assert_with_error (p, "My custom error message.");

return [list([]) as list<operation>, s];

};