小编Zub*_*ani的帖子

'a和之间有什么区别'_l？

我正在看这个错误,无法理解它:

Error: This expression has type ('a -> float polynomial) list but an expression was expected of type float polynomial list derivlist: ('_l ? float polynomial) list

module <name> =
   struct 
     .. 
   end;;


module type <name> =
    struct (* should have been sig *)
      .. 
end;;

module type ELEMENT =
sig
    type element_i
end

module Element:ELEMENT =
struct  
    type element_i =  N of int | CNN of cnn
end

module type SEMIRING =
functor (E:ELEMENT)->
sig
    type elements
end

module Semiring:SEMIRING =
functor(Element:ELEMENT) ->
struct
        let zero = (Element.element_i  0) (*ERROR: Unbounded Value; Same with N 0*)
end

如何在Semiring模块中创建element_i类型的对象？