The Leo Language

• All code examples can be copied and pasted into main.leo directly and executed with cargo run
• Programs should be formatted:
  1. Import definitions
  2. Struct definitions
  3. Function definitions

Integers:

Currently, all integers are parsed as u32. You can choose to explicitly add the type or let the compiler interpret implicitly.

function main() -> u32 {
    let a : u32 = 1u32 + 1u32; // explicit type
    let b = 1 - 1; // implicit type
    let c = 2 * 2;
    let d = 4 / 2;
    let e = 2 ** 3;
    return a
}

Field Elements:

Field elements must have the type added explicitly.

function main() -> fe {
    let f : fe = 21888242871839275222246405745257275088548364400416034343698204186575808495617fe;
    let a = 1fe + 1fe;
    let b = 1fe - 1fe;
    let c = 2fe * 2fe;
    let d = 4fe / 2fe;
    return a
}

Operator Assignment Statements:

function main() -> u32 {
  let a = 10;
  a += 5;
  a -= 10;
  a *= 5;
  a /= 5;
  a **= 2;

  return a
}

Booleans:

function main() -> bool {
    let a : bool = true || false;
    let b = false && false;
    let c = 1 == 1;
    return a
}

Arrays:

Leo supports static arrays with fixed length. Array type must be explicitly stated

function main() -> u32[2] {
    // initialize an integer array with integer values
    let a : u32[3] = [1, 2, 3];

    // set a member to a value
    a[2] = 4;

    // initialize an array of 4 values all equal to 42
    let b = [42; 4];

    // initialize an array of 5 values copying all elements of b using a spread
    let c = [1, ...b];

    // initialize an array copying a slice from `c`
    let d = c[1..3];

    // initialize a field array
    let e = [5fe; 2];

    // initialize a boolean array
    let f = [true, false || true, true];

    // return an array
    return d
}

Structs:

struct Point {
    u32 x
    u32 y
}
function main() -> u32 {
    Point p = Point {x: 1, y: 0}
    return p.x
}

struct Foo {
    bool x
}
function main() -> Foo {
    let f = Foo {x: true};
    f.x = false;
    return f
}

Assert Equals:

This will enforce that the two values are equal in the constraint system.

function main() {
  assert_eq(45, 45);
  
  assert_eq(2fe, 2fe);
  
  assert_eq(true, true);
}

Conditionals:

If Else Ternary Expression

function main() -> u32 {
  let y = if 3==3 ? 1 : 5;
  return y
}

If Else Conditional Statement

function main(a: private bool, b: private bool) -> u32 {
  let res = 0;
  if (a) {
    res = 1;
  } else if (b) {
    res = 2;
  } else {
    res = 3;
  }
  return res
}

For loop

function main() -> fe {
  let a = 1fe;
  for i in 0..4 {
    a = a + 1fe;
  }
  return a
}

Functions:

function test1(a : u32) -> u32 {
  return a + 1
}

function test2(b: fe) -> fe {
  return b * 2fe
}

function test3(c: bool) -> bool {
  return c && true
}

function main() -> u32 {
  return test1(5)
}

Function Scope:

function foo() -> field {
  // return myGlobal <- not allowed
  return 42fe
}

function main() -> field {
  let myGlobal = 42fe;
  return foo()
}

Multiple returns:

Functions can return tuples whose types are specified in the function signature.

function test() -> (u32, u32[2]) {
    return 1, [2, 3]
}

function main() -> u32[3] {
    let (a, b) = test();
    // a, u32[2] b = test() <- explicit type also works
    return [a, ...b]
}

Parameters:

Main function arguments are allocated as public or private variables in the program's constaint system.

function main(a: private fe) -> fe {
  return a
}

function main(a: public fe) -> fe {
  return a
}

Function parameters are passed by value.

function test(a: u32) {
    a = 0;
}

function main() -> u32 {
    let a = 1;
    test(a);

    return a // <- returns 1
}

Imports:

Both struct and function imports are supported.

import all: * import alias: symbol as alias

/simple_import.leo

struct Point {
    u32 x
    u32 y
}

function test() -> (u32, u32[2]) {
    return 1, [2, 3]
}

/simple.leo

from "./simple_import" import {
    Point as Foo,
    test
};

// from "./simple_import" import * 

function main() -> (u32[3]) {
    let (a, b) = test();
    let p = Foo { x: 1, y: 2};
    return [a, ...b]
}

Leo CLI

Develop

leo new

To setup a new package, run:

leo new {$NAME}

This will create a new directory with a given package name. The new package will have a directory structure as follows:

- inputs # Your program inputs
- outputs # Your program outputs
- src
    - lib.leo # Your program library
    - main.leo # Your program
- tests
    - tests.leo # Your program tests
- Leo.toml # Your program manifest

leo init

To initialize an existing directory, run:

leo init

This will initialize the current directory with the same package directory setup.

leo build

To compile your program and verify that it builds properly, run:

leo build

leo test

To execute unit tests on your program, run:

leo test

Run

leo setup

To perform the program setup, producing a proving key and verification key, run:

leo setup

Leo uses cryptographic randomness from your machine to perform the setup. The proving key and verification key are stored in the target directory as .leo.pk and .leo.vk:

{$LIBRARY}/target/{$PROGRAM}.leo.pk
{$LIBRARY}/target/{$PROGRAM}.leo.vk

leo prove

To execute the program and produce an execution proof, run:

leo prove

Leo starts by checking the target directory for an existing .leo.pk file. If it doesn't exist, it will proceed to run leo setup and then continue.

Once again, Leo uses cryptographic randomness from your machine to produce the proof. The proof is stored in the target directory as .leo.proof:

{$LIBRARY}/target/{$PROGRAM}.leo.proof

leo verify

To verify the program proof, run:

leo verify

Leo starts by checking the target directory for an existing .leo.proof file. If it doesn't exist, it will proceed to run leo prove and then continue.

After the verifier is run, Leo will output either true or false based on the verification.

Remote

To use remote compilation features, start by authentication with:

leo login

You will proceed to authenticate using your username and password. Next, Leo will parse your Leo.toml file for remote = True to confirm whether remote compilation is enabled.

If remote compilation is enabled, Leo syncs your workspace so when you run leo build, leo test, leo setup and leo prove, your program will run the program setup and execution performantly on remote machines.

This speeds up the testing cycle and helps the developer to iterate significantly faster.

Publish

To package your program as a gadget and publish it online, run:

leo publish

Leo will proceed to snapshot your directory and upload your directory to the circuit manager. Leo will verify that leo build succeeds and that leo test passes without error.

If your gadget name has already been taken, leo publish will fail.

Deploy

To deploy your program to Aleo, run:

leo deploy

TODO

• Change target directory to some other directory to avoid collision.
• Figure out how leo prove should take in assignments.
• Come up with a serialization format for .leo.pk, .leo.vk, and .leo.proof.