public IHttpActionResult Post(string userId, string otherUserId)
{
var userRes = UserReader.Lookup(userId).SelectError(
error => error.Accept(UserLookupError.Switch(
onInvalidId: "Invalid user ID.",
onNotFound: "User not found.")));
var otherUserRes = UserReader.Lookup(otherUserId).SelectError(
error => error.Accept(UserLookupError.Switch(
onInvalidId: "Invalid ID for other user.",
onNotFound: "Other user not found.")));
var connect =
from user in userRes
from otherUser in otherUserRes
select Connect(user, otherUser);
return(connect.SelectBoth(Ok, BadRequest).Bifold());
}