所以對於這三個操作的,你似乎已經定義幫手函數執行的操作背後的邏輯。除此之外,除了修正這種邏輯以使其起作用外,還將這些功能拼接在一起形成功能execute_ops
。
如果這些值同時值構造你的數據類型的您不能命名功能insert
,delete
和setsize
。簡單地說,一旦定義了數據類型,然後定義了同一個作用域中的函數,這些函數就會影響值構造函數,並且使您無法表示類型爲的列表list_op。
重要的,我懷疑混淆的一點是,insert
,delete
和setsize
不是執行列表上的操作的函數。他們是值構造,就像leaf
和node
是用於製作二叉樹:
datatype tree = leaf | node of tree*int*tree
在insert
比較pos=h
沒有意義。列表中的元素與他們的位置不同。你希望在位置pos
插入X,不就是等於pos
的第一要素。值不一定等於它在其中出現的列表中的位置。
而且delete
是不幸的是完全沒有意義的;你的代碼說的是「如果數字n等於列表中的元素,則返回整個列表。否則,刪除元素並繼續刪除元素,直到出現這種情況,或者列表爲空。」
在delete
引發異常也沒有根據該定義必要的。
我不知道你不理解的setSize是什麼意思。它應該是一個設置列表大小的操作。如果大小小於當前長度,請重複賦值文本,刪除過多的元素,否則使用零延長列表的末尾。
這是解決分配的模板:
datatype list_op = insert of int*int | delete of int | setsize of int
fun insert_h (0, elem, x::xs) = ... (* insert elem instead of x *)
| insert_h (pos, elem, []) = ... (* list was too short *)
| insert_h (pos, elem, x::xs) = ... (* not there yet *)
fun setsize_h (0, xs) = ... (* wonder what list has size 0 *)
| setsize_h (n, []) = ... (* extend list n times more *)
| setsize_h (n, x::xs) = ... (* not there yet *)
fun delete_h (0, x::xs) = ... (* delete element at this position *)
| delete_h (n, []) = ... (* list was too short *)
| delete_h (n, x::xs) = ... (* not there yet *)
fun execute_ops [] xs = ... (* no more operations to execute *)
| execute_ops (list_op::list_ops) xs =
let val new_xs = (case list_op of
insert (pos, elem) => insert_h (pos, elem, xs)
| delete pos => delete_h (pos, xs)
| setsize size => setsize_h (size, xs))
in execute_ops list_ops new_xs
end
您可能希望測試這些功能,無論是單獨或組合使用execute_ops
:
val test_insert_h_1 = insert_h (2, 7, [1,2,3,4]) = [1,2,7,4]
val test_insert_h_2 = insert_h (9, 5, [1,2,3,4]) = [1,2,3,4,5]
val test_setsize_h_1 = setsize_h (2, [5,6,7,8]) = [5,6]
val test_setsize_h_2 = setsize_h (5, [1,2,3]) = [1,2,3,0,0]
val test_delete_h_1 = delete_h (3, [4,5,6,7,8]) = [4,5,6,8]
val test_delete_h_2 = delete_h (9, [1,2,3]) = [1,2,3]
val test_execute_ops_1 =
execute_ops [insert (0, 5), insert (1, 6), insert (2, 7)] [2,3,5] = [5,6,7]
val test_execute_ops_2 =
execute_ops [setsize 5, insert (4, 9)] [] = [0,0,0,0,9]
val test_execute_ops_3 =
execute_ops [setsize 6, insert (1, 5), delete 3] [8,8,8,8,9] = [8,5,8,9,0]