This function validates arrays and their items as shown in the example below. This function is a higher order rule as it uses a sub-rule to validate each item in the array input. This function should only throw errors from the sub-rule or the rulr.InvalidArrayError. Each error thrown from the sub-rule will be wrapped in rulr.KeyedValidationError and these errors will be combined and thrown as rulr.ValidationErrors.
import * as rulr from 'rulr'
const constrainToExample = rulr.array(rulr.number)
type Example = rulr.Static<typeof constrainToExample>
// number[]
// Valid
const example1: Example = constrainToExample([1])
// Valid
const example2: Example = constrainToExample([])
// Invalid
const example3: Example = constrainToExample(['1'])