class Steep::Interface::Block

def +(other)
  optional = self.optional? || other.optional?
  type = AST::Types::Proc.new(params: self.type.params | other.type.params,
                              return_type: AST::Types::Union.build(types: [self.type.return_type,
                                                                           other.type.return_type]))
  self.class.new(
    type: type,
    optional: optional
  )
end

def ==(other)
  other.is_a?(self.class) && other.type == type && other.optional == optional
end

def closed?
  type.closed?
end

def free_variables
  type.free_variables
end

def initialize(type:, optional:)
  @type = type
  @optional = optional
end

def map_type(&block)
  self.class.new(
    type: type.map_type(&block),
    optional: optional
  )
end

def optional?
  @optional
end

def subst(s)
  self.class.new(
    type: type.subst(s),
    optional: optional
  )
end

def to_optional
  self.class.new(
    type: type,
    optional: true
  )
end

def to_s
  "#{optional? ? "?" : ""}{ #{type.params} -> #{type.return_type} }"
end