effect-ts-laws/src/arbitrary/instances.js

effect-ts law testing using fast-check.

/**
 * `@effect/typeclass` instances for the `fast-check` Arbitrary type.
 * @module
 */
import { Covariant as CO } from '@effect/typeclass';
import { dual } from 'effect/Function';
import fc from 'fast-check';
import { testUnaryEquivalence } from './equivalence.js';
const map = dual(2, (self, f) => self.map(a => f(a)));
const flatMap = dual(2, (self, f) => self.chain(a => f(a)));
/**
 * Monad instance for `fc.Arbitrary`.
 * @category fast-check
 */
export const Monad = {
    map,
    imap: CO.imap(map),
    flatMap,
    of: fc.constant,
};
/**
 * Get an equivalence for `fc.Arbitrary<A>` from an equivalence of `A`.
 * Arbitraries are equal if they produce the same values for the same seeds.
 * Note this only means we were unable to find a counterexample to the
 * equivalence.
 * @category fast-check
 */
export const getEquivalence = (equalsA, parameters) => {
    const sample = (arbitrary) => (seed) => {
        const [result] = fc.sample(arbitrary, { seed, numRuns: 1 });
        /* v8 ignore next 1 */
        if (result === undefined)
            throw new Error('Could not sample.');
        return result;
    };
    return (self, that) => testUnaryEquivalence(fc.integer(), equalsA, parameters)(sample(self), sample(that));
};
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