pzol/monadic

helps dealing with exceptional situations, it comes from the sphere of functional programming and bringing the goodies I have come to love in Scala to my ruby projects

monadic's Issues

Cannot specify nil as the desired fetch value from Monadic:Nothing

Example:
I have a person object that might have a spouse object, and I want their first_name. So, if all is good, I'd call person.spouse.first_name. Of course, if we have no spouse there would be a crash of no method first_name on nil, so I use Maybe:

first_name = Maybe(person).spouse.first_name.fetch(nil)

In this case, as per idiomatic Ruby, I want nil as the default first_name if there is none. However, the value of first_name is not nil, but rather Monadic::Nothing, which is true valued in if satements! In other words

# Fails to work correctly because first name is Monadic::Nothing, not nil as expected!
do_something(first_name) if first_name

The bug is at https://github.com/pzol/monadic/blob/master/lib/monadic/maybe.rb#L78, where you use a magic value for the argument to decide if you have one, and that magic value happens to be a common default for idiomatic Ruby.

My recommended fix would be to capture the args as follows, which gives exactly the same behavior as the current version, but honors any default value:

def fetch(*args)
  case args.length
  when 0
    self
  when 1
    args.first
  else
    raise ArgumentError, "wrong number of arguments (#{args.length} for 0..1)", caller
  end
end

Bug: Maybe('foo').truly? != true

Maybe('foo').truly? == true no longer. In Ruby 2.0.0 it returns false:

2.0.0p247 :014 > Maybe('foo').truly?
false

Have you looked at rumonade?

The rumonade gem also offers Option and Either classes -- please let me know if there is missing functionality that you would like to see.