public void EitherFoldWhenLeft()
{
int state = 10;
int expected = 10;
Either <string, int> either = "10";
int result =
EitherModule.Fold(
(_state, right) => right + _state,
(_state, left) => _state,
state,
either);
Assert.AreEqual(expected, result);
}
/// <summary>
/// Creates a new <typeparamref name="TState"/> value by applying the given folder functions
/// to <paramref name="state"/> and <see cref="Either{TLeft, TRight}"/> value.
/// </summary>
/// <typeparam name="TLeft">The type of the left value.</typeparam>
/// <typeparam name="TRight">The type of the right value.</typeparam>
/// <typeparam name="TState">The type of initial and final states</typeparam>
/// <param name="folderWhenLeft">The function to transform either value from the input <paramref name="either"/> to a new state value.</param>
/// <param name="folderWhenRight">The function to transform either value from the input <paramref name="either"/> to a new state value.</param>
/// <param name="state">The initial state.</param>
/// <param name="either">the input either.</param>
/// <returns>
/// Returns a new <typeparamref name="TState"/> value by applying the given folder functions
/// to <paramref name="state"/> and <see cref="Either{TLeft, TRight}"/> value.
/// </returns>
public static TState Fold <TLeft, TRight, TState>(this Either <TLeft, TRight> either, TState state, Func <TState, TRight, TState> folderWhenRight, Func <TState, TLeft, TState> folderWhenLeft)
=> EitherModule.Fold(folderWhenRight, folderWhenLeft, state, either);
