I recently received a confusing error message from union validation. Take the following as an example... a simple union of 2 objects:

import * as t from 'runtypes'

const S = t.String.withConstraint((x) => x === 'bar' || 'Should be bar')

const R = t.Record({ s: S }).Or(t.Record({ t: S }))

try {
  R.check({ s: 'rab' })
} catch (error) {
  console.error(error)
}

This produces:

ValidationError: Expected { s: string; } | { t: string; }, but was object
    at ...
    <stack traces>
    at ... {
  code: 'TYPE_INCORRECT'
}

The message Expected { s: string; } | { t: string; }, but was object isn't all that helpful. Can this message be improved somehow?