functional-programming - 为什么 ocamlc 说我不匹配 {} 而我没有？

Question

我写了myPercolation.ml。

open MyUnionFind

module type MyPercolationSig = sig
  type percolation
  val create_percolation : int -> percolation
  val open_site : percolation -> int -> int -> unit
  val is_open : percolation -> int -> int -> bool
  val is_full : percolation -> int -> int -> bool
  val can_percolates : percolation -> bool
end

module MyPercolation : MyPercolationSig = struct

  exception IndexOutOfBounds;;

  type percolation = 
      {n : int; 
       sites: bool array; 
       union : MyUnionFind.union_find};;

  let create_percolation n = 
    {n = n; sites = Array.make (n*n) false; union = MyUnionFind.create_union (n*n)};;

  let open_site p i j = 
    let {n;_;union} = p 
    in 
    if not (is_open p i j) then
      begin 
    sites.(index_of n i j) <- true;
    if i - 1 >= 1 && i - 1 <= n && is_open n (i-1) j then
      MyUnionFind.union union (index_of n i j) (index_of n (i-1) j)
    else  if i + 1 >= 1 && i + 1 <= n && is_open n (i+1) j then
      MyUnionFind.union union (index_of n i j) (index_of n (i+1) j)
    else  if j - 1 >= 1 && j - 1 <= n && is_open n i (j-1) then
      MyUnionFind.union union (index_of n i j) (index_of n i (j-1))
    else  if j + 1 >= 1 && j + 1 <= n && is_open n i (j+1) then
      MyUnionFind.union union (index_of n i j) (index_of n i (j+1))
      end;;

  let index_of n i j = n * (i - 1) + j;;

  let is_open {n;sites;_} i j = 
    if i < 1 || i > n || j < 1 || j > n then 
      raise IndexOutOfBounds
    else 
      sites.(index_of n i j);;

  let is_full {n;_;union} i j =
    let rec is_connected_top j' =
      if j = 0 then false
      else 
    if MyUnionFind.is_connected union (index_of n i j) (index_of n 0 j') then true
    else is_connected_top (j'-1)
    in is_connected_top n;;

  let can_percolates p =
    let {n;_;_} = p 
    in  
    let rec is_full_bottom j =
      if j = 0 then false
      else 
    if is_full p n j then true
    else is_full_bottom (j-1)


end

---

请忽略包 MyUnionFind 包。它只是union-find算法的自制实现。

当我尝试编译 myPercolation.ml 时，出现这样的错误:

$ ocamlc -c myPercolation.ml
File "myPercolation.ml", line 25, characters 11-12:
Error: Syntax error: '}' expected
File "myPercolation.ml", line 25, characters 8-9:
Error: This '{' might be unmatched

我认为错误是在 let open_site p i j 的函数中谈论 let {n;_;union} = p。

我已经多次阅读该行和所有代码，但我仍然没有看到该行中有任何不匹配的 {}。

有人可以帮忙吗？

Answer 1

另一个可能的错误:{n;_;_} 应该是 {n;_} 只有 1 个下划线是必要的。可以把它想象成匹配语句中的 _ 通配符。