Loops

Compact supports bounded for loops. Loops must have statically known bounds.

Two Forms

for (const i of <lower>..<upper>) <statement>

for (const item of <vector>) <statement>

Iterating Over a Range

pragma language_version >= 0.16;

import CompactStandardLibrary;

export ledger results: Map<Field, Field>;

export circuit storeRange(): [] {
    for (const i of 0..5) {
        results.insert(disclose(i), disclose(i) * (2 as Field));
    }
}

Iterating Over a Vector

pragma language_version >= 0.16;

import CompactStandardLibrary;

export ledger total: Counter;

export circuit processVector(values: Vector<5, Uint<16>>): [] {
    for (const v of values) {
        total.increment(disclose(v));
    }
}

Accumulation with Fold

Since Compact only has const bindings (no mutable variables), use fold for accumulation:

pragma language_version >= 0.16;

import CompactStandardLibrary;

export pure circuit sumVector(values: Vector<4, Uint<64>>): Uint<64> {
    const result = fold(
        (acc: Uint<64>, val: Uint<64>): Uint<64> => {
            return (acc + val) as Uint<64>;
        },
        0 as Uint<64>,
        values
    );
    return result;
}

Const Bindings and Blocks

Within loops, you can use const bindings:

const x = <expr>;
const x: T = <expr>, y = <expr>;

Rules:

Bindings are evaluated left-to-right
No use-before-definition
No rebinding in the same block
Shadowing allowed in nested blocks

Source: Statements

Next Steps

Learn about Functions in Compact.

Learn Compact