compact-corelanguage-reference

name	compact-core:language-reference
description	Use when writing Compact smart contracts and need reference for primitive types (Field, Boolean, Uint), composite types (struct, enum, Vector, Bytes), circuit/witness syntax, control flow (if/else, for loops, assert), or module system (import, include, export).

Compact Language Reference

Complete reference for the Compact smart contract language used on Midnight Network.

Quick Reference

Primitive Types

Type	Description	Example
Field	ZK-native field element (~254 bits)	const f: Field = 42;
Boolean	True/false value	const b: Boolean = true;
Uint<N>	Unsigned integer (N bits, N ≤ 248)	const n: Uint<64> = 100;

Composite Types

Type	Description	Example
Bytes<N>	Fixed-size byte array	const h: Bytes<32> = ...;
struct	Named record type	struct Point { x: Field, y: Field }
enum	Tagged union	enum Maybe<T> { Some(T), None }
Vector<T, N>	Fixed-size array	const v: Vector<Field, 3> = [1, 2, 3];

Special Types

Type	Description	Example
Opaque<'string'>	UTF-8 string from TypeScript	witness get_name(): Opaque<'string'>;
Opaque<'Uint8Array'>	Binary data from TypeScript	witness get_data(): Opaque<'Uint8Array'>;

Circuit Syntax

// Public circuit callable from TypeScript
export circuit transfer(to: Bytes<32>, amount: Uint<64>): [] {
    // Circuit body
}

// Private helper circuit
circuit helper(x: Field): Field {
    return x * x;
}

Witness Syntax

// Declaration (implemented in TypeScript)
witness get_private_key(): Bytes<32>;

// Usage in circuit
export circuit sign(message: Bytes<32>): Bytes<64> {
    const key = get_private_key();
    // Use key...
}

Control Flow

// Conditional
if (condition) {
    // then branch
} else {
    // else branch
}

// Bounded loop (bounds must be compile-time constant)
for i in 0..10 {
    // loop body
}

// Assertion
assert condition, "Error message";

Module System

// Import specific items
import { hash } from "CompactStandardLibrary";

// Include entire file
include "utils.compact";

// Export for external use
export circuit public_fn(): Field { ... }

References

For detailed documentation on each topic:

• Type System - Complete type reference with constraints
• Circuits - Circuit and witness patterns
• Control Flow - Conditionals, loops, assertions
• Modules - Import, include, export, COMPACT_PATH