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module type DICTIONARY = sig
  type key = string
  type 'a t
 
  val empty : 'a t
  val insert : key -> 'a -> 'a t -> 'a t
  val lookup : key -> 'a t -> 'a option
  val map : ('a -> 'b) -> 'a t -> 'b t
end
 
module type DICTIONARY_PLUS = sig
  include DICTIONARY
  val size : 'a t -> int
end
 
module AssocList : DICTIONARY = struct
  type key = string
  type 'a t = (key * 'a) list
 
  let empty = []
 
  let insert k v dict =
    (k, v) :: dict
 
  let rec lookup k dict =
    match dict with
      | [] -> None
      | (k',v)::dict' ->
          if k = k' then Some v
          else lookup k dict'
 
  let rec map fn dict =
    List.map (fun (k, v) -> (k, fn v)) dict
end
 
module AssocListPlus : DICTIONARY_PLUS = struct
  include AssocList
  let size = List.length
end

File "prog.ml", line 36, characters 41-96:
Signature mismatch:
Modules do not match:
  sig
    type key = string
    type 'a t = 'a AssocList.t
    val empty : 'a t
    val insert : key -> 'a -> 'a t -> 'a t
    val lookup : key -> 'a t -> 'a option
    val map : ('a -> 'b) -> 'a t -> 'b t
    val size : 'a list -> int
  end
is not included in
  DICTIONARY_PLUS
Values do not match:
  val size : 'a list -> int
is not included in
  val size : 'a t -> int

Standard output is empty