mirror of
https://github.com/AleoHQ/leo.git
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706 lines
15 KiB
Markdown
706 lines
15 KiB
Markdown
# The Leo Programming Language
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[](https://travis-ci.com/AleoHQ/leo)
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[](https://codecov.io/gh/AleoHQ/leo)
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## Compiler Architecture
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<!-- generated by mermaid compile action - START -->
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<details>
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<summary>Mermaid markup</summary>
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```mermaid
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graph LR
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Pass1(Syntax Parser) -- ast --> Pass2(Type Resolver)
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Pass2 -- imports --> Pass3(Import Resolver)
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Pass3 -- statements --> Pass4
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Pass2 -- statements --> Pass4(Synthesizer)
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Pass4 -- constraints --> Pass5(Program)
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```
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</details>
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<!-- generated by mermaid compile action - END -->
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## Language Specification
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* Programs should be formatted:
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1. Import definitions
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2. Circuit definitions
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3. Function definitions
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## Defining Variables
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Leo supports `let` and `const` keywords for variable definition.
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```let a = true;``` defines an **allocated** program variable `a` with boolean value `true`.
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```const a = true;``` defines a **constant** program variable `a` with boolean value `true`.
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**Allocated** variables define private variables in the constraint system. Their value is constrained in the circuit on initialization.
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**Constant** variables do not define a variable in the constraint system. Their value is constrained in the circuit on computation with an **allocated** variable.
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**Constant** variables can be mutable. They do not have the same functionality as `const` variables in other languages.
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```rust
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function addOne() -> {
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let a = 0u8; // allocated, value enforced on this line
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const b = 1u8; // constant, value not enforced yet
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return a + b // allocated, computed value is enforced to be the sum of both values
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}
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```
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Computations are expressed in terms of arithmetic circuits, in particular rank-1 quadratic constraint systems. Thus computing on an allocated variable always results in another allocated variable.
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## Mutability
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* All defined variables in Leo are immutable by default.
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* Variables can be made mutable with the `mut` keyword.
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```rust
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function main() {
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let a = 0u32;
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//a = 1 <- Will fail
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let mut b = 0u32;
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b = 1; // <- Ok
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}
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```
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## Booleans
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Explicit types are optional.
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```rust
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function main() -> bool {
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let a: bool = true || false;
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let b = false && false;
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let c = 1u32 == 1u32;
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return a
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}
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```
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## Numbers
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* The definition of a number must include an explicit type.
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* After assignment, you can choose to explicitly add the type or let the compiler interpret implicitly.
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* Type casting is not supported.
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* Comparators are not supported.
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### Integers
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Supported integer types: `u8`, `u16`, `u32`, `u64`, `u128`
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```rust
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function main() -> u32 {
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let a = 2u32; // explicit type
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let a: u32 = 1 + 1; // explicit type
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let b = a - 1; // implicit type
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let c = b * 4;
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let d = c / 2;
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let e = d ** 3;
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return e
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}
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```
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### Field Elements
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```rust
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function main() -> field {
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let a = 1000field; // explicit type
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let a: field = 21888242871839275222246405745257275088548364400416034343698204186575808495617; // explicit type
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let b = a + 1; // implicit type
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let c = b - 1;
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let d = c * 4;
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let e = d / 2;
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return e
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}
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```
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### Affine Points
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The set of affine points on the elliptic curve passed into the leo compiler forms a group.
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Leo supports this set as a primitive data type.
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```rust
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function main() -> group {
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let a = 1000group; // explicit type
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let a = (21888242871839275222246405745257275088548364400416034343698204186575808495617, 21888242871839275222246405745257275088548364400416034343698204186575808495617)group; // explicit type
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let b = a + 0; // implicit type
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let c = b - 0;
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return c
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}
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```
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### Operator Assignment Statements
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```rust
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function main() -> u32 {
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let mut a = 10;
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a += 5;
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a -= 10;
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a *= 5;
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a /= 5;
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a **= 2;
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return a
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}
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```
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## Arrays
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Leo supports static arrays with fixed length.
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```rust
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function main() -> u32[2] {
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// initialize an integer array with integer values
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let mut a: u32[3] = [1, 2, 3];
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// set a mutable member to a value
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a[2] = 4;
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// initialize an array of 4 values all equal to 42
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let b = [42u8; 4];
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// initialize an array of 5 values copying all elements of b using a spread
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let c = [1, ...b];
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// initialize an array copying a slice from `c`
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let d = c[1..3];
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// initialize a field array
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let e = [5field; 2];
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// initialize a boolean array
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let f = [true, false || true, true];
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return d
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}
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```
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### Multidimensional Arrays
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```rust
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function main() -> u32[3][2] {
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let m = [[0u32, 0u32], [0u32, 0u32]];
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let m: u32[3][2] = [[0; 3]; 2];
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return m
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}
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```
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## Conditionals
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Branching in Leo is different than traditional programming languages. Leo developers should keep in mind that every program compiles to a circuit which represents
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all possible evaluations.
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### If Else Ternary Expression
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Ternary `if [cond] ? [first] : [second];` expressions are the cheapest form of conditional.
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Since `first` and `second` are expressions, we can resolve their values before proceeding execution.
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In the underlying circuit, this is a single bit multiplexer.
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```rust
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function main() -> u32 {
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let y = if 3==3 ? 1 : 5;
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return y
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}
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```
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### If Else Conditional Statement
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Leo supports the traditional `if [cond] { [first] } else { [second] }` which can be chained using `else if`.
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Since `first` and `second` are one or more statements, they resolve to separate circuits which will all be evaluated.
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In the underlying circuit this can be thought of as a demultiplexer.
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```rust
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function main(a: bool, b: bool) -> u32 {
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let mut res = 0u32;
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if a {
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res = 1;
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} else if b {
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res = 2;
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} else {
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res = 3;
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}
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return res
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}
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```
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### For loop
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```rust
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function main() -> fe {
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let mut a = 1field;
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for i in 0..4 {
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a = a + 1;
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}
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return a
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}
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```
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## Functions
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```rust
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function test1(a : u32) -> u32 {
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return a + 1
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}
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function test2(b: fe) -> field {
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return b * 2field
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}
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function test3(c: bool) -> bool {
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return c && true
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}
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function main() -> u32 {
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return test1(5)
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}
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```
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### Function Scope
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```rust
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function foo() -> field {
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// return myGlobal <- not allowed
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return 42field
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}
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function main() -> field {
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let myGlobal = 42field;
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return foo()
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}
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```
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### Multiple returns
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Functions can return tuples whose types are specified in the function signature.
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```rust
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function test() -> (u32, u32[2]) {
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return 1, [2, 3]
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}
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function main() -> u32[3] {
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let (a, b) = test();
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// (a, u32[2] b) = test() <- explicit type also works
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return [a, ...b]
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}
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```
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### Function inputs
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Main function inputs are allocated private variables in the program's constraint system.
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`a` is implicitly private.
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```rust
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function main(a: field) -> field {
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return a
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}
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```
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Normal function inputs are passed by value.
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```rust
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function test(mut a: u32) {
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a = 0;
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}
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function main() -> u32 {
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let a = 1;
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test(a);
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return a // <- returns 1
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}
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```
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## Circuits
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Circuits in Leo are similar to classes in object oriented langauges. Circuits are defined above functions in a Leo program. Circuits can have one or more members.
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Members can be defined as fields which hold primitive values
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```rust
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circuit Point {
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x: u32
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y: u32
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}
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function main() -> u32 {
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let p = Point {x: 1, y: 0};
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return p.x
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}
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```
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Members can also be defined as functions.
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```rust
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circuit Circ {
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function echo(x: u32) -> u32 {
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return x
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}
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}
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function main() -> u32 {
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let c = Circ { };
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return c.echo(1u32)
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}
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```
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Circuit functions can be made static, enabling them to be called without instantiation.
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```rust
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circuit Circ {
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static function echo(x: u32) -> u32 {
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return x
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}
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}
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function main() -> u32 {
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return Circ::echo(1u32)
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}
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```
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The `Self` keyword is supported in circuit functions.
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```rust
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circuit Circ {
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b: bool
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static function new() -> Self {
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return Self { b: true }
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}
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}
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function main() -> Circ {
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let c = Circ::new();
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return c.b
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}
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```
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## Imports
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Leo supports importing functions and circuits by name into the current file with the following syntax:
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```rust
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import [package].[name];
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```
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#### Import Aliases
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To import a name using an alias:
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```rust
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import [package].[name] as [alias];
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```
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#### Import Multiple
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To import multiple names from the same package:
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```rust
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import [package].(
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[name_1],
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[name_2] as [alias],
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);
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```
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#### Import Star
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To import all symbols from a package:
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```rust
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import [package].*;
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```
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### Local
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You can import from a local file in the `src/` directory by using its `[file].leo` as the `[package]` name.
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```rust
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import [file].[name];
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```
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#### Example:
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`src/bar.leo`
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```rust
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circuit Bar {
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b: u32
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}
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function baz() -> u32 {
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return 1u32
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}
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```
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`src/main.leo`
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```rust
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import bar.(
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Bar,
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baz
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);
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function main() {
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const bar = Bar { b: 1u32};
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const z = baz();
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}
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```
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### Foreign
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You can import from a foreign package in the `imports/` directory using its `[package]` name.
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```rust
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import [package].[name];
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```
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#### Example:
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`imports/bar/src/lib.leo`
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```rust
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circuit Bar {
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b: u32
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}
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```
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`src/main.leo`
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```rust
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import bar.Bar;
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function main() {
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const bar = Bar { b: 1u32 };
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}
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```
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### Package Paths
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Leo treats directories as package names when importing.
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```rust
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import [package].[directory].[file].[name]
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```
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#### Example:
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We wish to import the `Baz` circuit from the `baz.leo` file in the `bar` directory in the `foo` package
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`imports/foo/src/bar/baz.leo`
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```rust
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circuit Baz {
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b: u32
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}
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```
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`src/main.leo`
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```rust
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import foo.bar.baz.Baz;
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function main() {
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const baz = Baz { b: 1u32 };
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}
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```
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## Constraints
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### Assert Equals
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This will enforce that the two values are equal in the constraint system.
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```rust
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function main() {
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assert_eq!(45, 45);
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assert_eq!(2fe, 2fe);
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assert_eq!(true, true);
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}
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```
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## Testing
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Use the `test` keyword to add tests to a leo program. Tests must have 0 function inputs and 0 function returns.
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```rust
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function main(a: u32) -> u32 {
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return a
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}
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test function expect_pass() {
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let a = 1u32;
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let res = main(a);
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assert_eq!(res, 1u32);
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}
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test function expect_fail() {
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assert_eq!(1u8, 0u8);
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}
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```
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# Leo Inputs
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Private inputs for a Leo program are specified in the `inputs/` directory. The syntax for an input file is a limited subset of the Leo program syntax. The default inputs file is `inputs/inputs.leo`.
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## Sections
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A Leo input file is made up of sections. Sections are defined by a section header in brackets followed by one or more input definitions.
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Section headers specify the target file which must have a main function with matching input names and types.
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`inputs/inputs.leo`
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```rust
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[main] // <- section header
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a: u32 = 1;
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b: u32 = 2;
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```
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`src/main.leo`
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```rust
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function main(a: u32, b: u32) -> u32 {
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let c: u32 = a + b;
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return c
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}
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```
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## Input Definitions
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### Supported types
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```rust
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[main]
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a: bool = true; // <- booleans
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b: u8 = 2; // <- integers
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c: field = 0; // <- fields
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d: group = (0, 1)group // <- group tuples
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```
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### Arrays
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```rust
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[main]
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a: u8[4] = [0u8; 4]; // <- single
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b: u8[2][3] = [[0u8; 2]; 3]; // <- multi-dimensional
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```
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# Leo CLI
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## Develop
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### `leo new`
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To setup a new package, run:
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```
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leo new {$NAME}
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```
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This will create a new directory with a given package name. The new package will have a directory structure as follows:
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```
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- inputs # Your program inputs
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- inputs.leo # Your program inputs for main.leo
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- outputs # Your program outputs
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- src
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- main.leo # Your program
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- tests
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- test.leo # Your program tests
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- Leo.toml # Your program manifest
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```
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#### Flags
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```rust
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leo new {$Name} --bin
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```
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This will create a new directory with a given package name. The new package will have a directory structure as above.
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```rust
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leo new {$Name} --lib
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```
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This will create a new directory with a given package name. The new package will have a directory structure as follows:
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```
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- src
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- lib.leo # Your program library
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- Leo.toml # Your program manifest
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```
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### `leo init`
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To initialize an existing directory, run:
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```
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leo init
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```
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This will initialize the current directory with the same package directory setup.
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#### Flags
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`leo init` supports the same flags as `leo new`
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```rust
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leo init --bin
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```
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```rust
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leo init --lib
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```
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### `leo build`
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To compile your program and verify that it builds properly, run:
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```
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leo build
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```
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### `leo test`
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To execute unit tests on your program, run:
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```
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leo test
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```
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The results of test compilation and the constraint system will be printed:
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```
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INFO leo Running 2 tests
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INFO leo test language::expect_pass compiled. Constraint system satisfied: true
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ERROR leo test language::expect_fail errored: Assertion 1u8 == 0u8 failed
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```
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## Run
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### `leo setup`
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To perform the program setup, producing a proving key and verification key, run:
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```
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leo setup
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```
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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/{$PROGRAM}.leo.vk
|
|
```
|
|
|
|
### `leo prove`
|
|
|
|
To execute the program and produce an execution proof, run:
|
|
```
|
|
leo prove
|
|
```
|
|
Leo starts by checking the `target` directory for an existing `.leo.pk` file. If it doesn't exist, it will proceed to run `leo setup` and then continue.
|
|
|
|
Next any input files in the `inputs` directory are parsed and all input values are passed to the program.
|
|
|
|
Once again, Leo uses cryptographic randomness from your machine to produce the proof. The proof is stored in the `target` directory as `.leo.proof`:
|
|
|
|
```
|
|
{$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
|
|
```
|
|
|
|
# Install
|
|
|
|
To install Leo from source, in the root directory of the repository, run:
|
|
```
|
|
cargo install --path .
|
|
```
|
|
|
|
## 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`.
|