Hello World

The Contract

View Contract Code

pragma language_version >= 0.23;

import CompactStandardLibrary;

// On-chain storage for the message
export ledger message: Opaque<"string">;

// Store a new message
export circuit storeMessage(customMessage: Opaque<"string">): [] {
    message = disclose(customMessage);
}

// Retrieve the current message
export circuit getMessage(): Opaque<"string"> {
    return message;
}

How It Works

Pragma Directive

pragma language_version >= 0.23;

Specifies the minimum Compact compiler version this contract supports.

Import Statement

import CompactStandardLibrary;

Provides built-in types like Opaque, Bytes, and stdlib functions.

Ledger Declaration

export ledger message: Opaque<"string">;

Declares on-chain state. Opaque<"string"> stores a variable-length byte sequence whose value is opaque to the circuit (hashed inside ZK, full value visible off-chain).

Circuits (Functions)

export circuit storeMessage(customMessage: Opaque<"string">): [] {
    message = disclose(customMessage);
}

circuit declares a function that compiles to a zero-knowledge circuit. export makes it callable from outside the contract. [] is the empty-tuple unit type — the circuit returns nothing.

The disclose() Function

message = disclose(customMessage);

Opaque<"string"> values are treated as witness-tainted: the compiler refuses to write them to the public ledger unless you explicitly disclose them. disclose(x) is a compiler annotation that says “I know this value flows from a private/witness source to a public location and that’s intentional.” If you tried message = customMessage without disclose, the compiler would reject it with:

potential witness-value disclosure must be declared but is not

Every circuit parameter requires disclose() when it flows directly into a ledger write, regardless of its type. The compiler is conservative: it doesn’t know whether a given call site supplies the parameter from a public source or from witness data, so it forces you to declare the disclosure explicitly at every ledger boundary.

Getting Started

Basics

Applications

The Contract

How It Works

Pragma Directive

Import Statement

Ledger Declaration

Circuits (Functions)

The disclose() Function

What’s Next

First App - Counter

Primitive Types

​The Contract

​How It Works

​Pragma Directive

​Import Statement

​Ledger Declaration

​Circuits (Functions)

​The disclose() Function

​What’s Next

First App - Counter

Primitive Types

The Contract

How It Works

Pragma Directive

Import Statement

Ledger Declaration

Circuits (Functions)

The disclose() Function

What’s Next