untitled notebook

const fc = require('fast-check'); function binaryAssociativeFunction(arb) { return fc.tuple( fc.set(arb, {minLength: 100, maxLength: 100, compare: (a, b) => fc.stringify(a) === fc.stringify(b)}), fc.constantFrom( length => (a, b) => (a + b) % length, length => (a, b) => (a * b) % length, // Come up with more... ) ) .map(([dataset, createAssociativeF]) => { const associativeF = createAssociativeF(dataset.length); const stringifiedDataset = new Map(dataset.map((d, index) => [fc.stringify(d), index])) return (a, b) => { // compute index for a const stringifiedA = fc.stringify(a); const indexA = stringifiedDataset.has(stringifiedA) ? stringifiedDataset.get(stringifiedA) : fc.hash(stringifiedA) % dataset.length; // compute index for b const stringifiedB = fc.stringify(b); const indexB = stringifiedDataset.has(stringifiedB) ? stringifiedDataset.get(stringifiedB) : fc.hash(stringifiedB) % dataset.length; // compute answer const indexResult = associativeF(indexA, indexB); if (!(indexA in dataset)) throw new Error('unexpected: invalid indexA'); if (!(indexB in dataset)) throw new Error('unexpected: invalid indexB'); if (!(indexResult in dataset)) throw new Error('unexpected: invalid indexResult'); return dataset[indexResult]; }; }) } // Just trying with one of the generated functions const a = 'a'; const b = 'b'; const c = 'c'; const f1 = fc.sample(binaryAssociativeFunction(fc.string()), 1)[0]; console.log('a,b -> ' + f1(a, b)); console.log('(a,b),c -> ' + f1(f1(a, b), c)); console.log('b,c -> ' + f1(b, c)); console.log('a,(b,c) -> ' + f1(a, f1(b, c))); // Property to confirm it works fc.assert(fc.property( binaryAssociativeFunction(fc.string()), fc.string(), fc.string(), fc.string(), (f, a, b, c) => f(f(a,b),c) === f(a,f(b,c)))); console.log('Done!');