Clojure的core.logic計數元素

Question

我嘗試做這樣的事情在core.logic

(defn count-different-elements-in-list [coll] 
    (count (set coll))) 

這部作品與整數就好

(should= 1 (count-different-elements-in-list '(1 1 1))) 
(should= 2 (count-different-elements-in-list '(1 1 2))) 
(should= 3 (count-different-elements-in-list '(1 3 2))) 

，但現在我想使用core.logic來解決一些東西，那裏得到的雜亂

(run* [a b c] 
    ;;the variables get values between 1 and 3 
    (fd/in a b c (fd/interval 1 3)) 
    ;; in the list there should only be 2 different values 
    (== 2 (count-different-elements-in-list '(a b c)))) 

但是問題出在這裏，abc沒有得到pas sed作爲函數的值。它們作爲變量傳遞。有三個變量count-different-elements-in-list返回值始終爲3，而core.logic找不到解決方案（空列表）。

但我正在尋找這個結果。

([1 1 2] [1 2 1] [2 1 1] 
[1 1 3] [1 3 1] [3 1 1] 
[2 2 1] [2 1 2] [1 2 2] 
[2 2 3] [2 3 2] [3 2 2] 
[3 3 1] [3 1 3] [1 3 3] 
[3 3 2] [3 2 3] [2 3 3]) 

Answer 1

您需要core.logic/project邏輯瓦爾成非關係的目標，像正常功能count-different-elements-in-list。不幸的是，您不能限制爲單個值的有限域邏輯變量，如a,b和c。 （見：this question）

在你有例如，可以換出fd/in和fd/interval用於生成範圍和membero。這將刪除無約束的有限域變量，保持整數的範圍約束，並允許投影。

(def interval (vec (range 1 4))) 
(run* [a b c] 
    (membero a interval) 
    (membero b interval) 
    (membero c interval) 
    (project [a b c] 
    (== 2 (count-different-elements-in-list (list a b c)))))