class Dentaku::AST::FunctionRegistry

def self.arity
  @implementation.arity < 0 ? nil : @implementation.arity
end

def self.default
  Dentaku::AST::Function.registry
end

def self.implementation
  @implementation
end

def self.implementation=(impl)
  @implementation = impl
end

def self.name
  @name
end

def self.name=(name)
  @name = name
end

def self.type
  @type
end

def self.type=(type)
  @type = type
end

def default
  self.class.default
end

def function_name(name)
  name.to_s.downcase
end

def get(name)
  name = function_name(name)
  return self[name] if has_key?(name)
  return default[name] if default.has_key?(name)
  nil
end

def register(name, type, implementation)
  function = Class.new(Function) do
    def self.name=(name)
      @name = name
    end
    def self.name
      @name
    end
    def self.implementation=(impl)
      @implementation = impl
    end
    def self.implementation
      @implementation
    end
    def self.type=(type)
      @type = type
    end
    def self.type
      @type
    end
    def self.arity
      @implementation.arity < 0 ? nil : @implementation.arity
    end
    def value(context = {})
      args = @args.map { |a| a.value(context) }
      self.class.implementation.call(*args)
    end
    def type
      self.class.type
    end
  end
  function.name = name
  function.type = type
  function.implementation = implementation
  self[function_name(name)] = function
end

def register_class(name, function_class)
  self[function_name(name)] = function_class
end

def type
  self.class.type
end

def value(context = {})
  args = @args.map { |a| a.value(context) }
  self.class.implementation.call(*args)
end