import { Either, isLeft } from './Either'

import { curry } from '@typed/lambda'
import { fromRight } from './Right'

/**
 * Returns a `Either` that is the result of calling `f` with the resolved
 * value of another `Either`.
 * @name chain<A, B, C>(f: (value: B) => Either<A, C>, either: Either<A, B>): Either<A C>
 */
export const chain = curry(__chain) as {
  <A, B, C>(f: (value: B) => Either<A, C>, either: Either<A, B>): Either<A, C>
  <A, B, C>(f: (value: B) => Either<A, C>): (either: Either<A, B>) => Either<A, C>
}

function __chain<A, B, C>(f: (value: B) => Either<A, C>, either: Either<A, B>): Either<A, C> {
  return isLeft(either) ? either : f(fromRight(either))
}