class Steep::AST::Types::Nil

def ==(other) 

def ==(other)
  other.is_a?(Nil)
end

def back_type 

def back_type
  Name::Instance.new(name: Builtin::NilClass.module_name,
                     args: [])
end

def hash 

def hash
  self.class.hash
end

def level 

def level
  [0]
end

def subst(s) 

def subst(s)
  self
end

def to_s 

def to_s
  "nil"
end