Skip to main content
Version: 0.5.1


Functions in Noir follow the same semantics of Rust, though Noir does not support early returns.

To declare a function the fn keyword is used.

fn foo() {}

All parameters in a function must have a type and all types are known at compile time. The parameter is pre-pended with a colon and the parameter type. Multiple parameters are separated using a comma.

fn foo(x : Field, y : pub Field){}

The return type of a function can be stated by using the -> arrow notation. The function below states that the foo function must return a Field. If the function returns no value, then the arrow is omitted.

fn foo(x : Field, y : pub Field) -> Field {
x + y

Note that a return keyword is unneeded in this case - the last expression in a function's body is returned.

Call Expressions

Calling a function in Noir is executed by using the function name and passing in the necessary arguments.

Below we show how to call the foo function from the main function using a call expression:

fn main(x : Field, y : Field) {
let z = foo(x);

fn foo(x : Field) -> Field {
x + x


You can define methods in Noir on any struct type in scope.

struct MyStruct {
foo: Field,
bar: Field,

impl MyStruct {
fn new(foo: Field) -> MyStruct {
MyStruct {
bar: 2,

fn sum(self) -> Field { +

fn main() {
let s = MyStruct::new(40);
constrain s.sum() == 42;

Methods are just syntactic sugar for functions, so if we wanted to we could also call sum as follows:

constrain MyStruct::sum(s) == 42