在OCaml中操作循环内的不可变变量 [英] Manipulate unmutable variables inside of loop in OCaml

问题描述

我在OCaml中有下面的代码。我已经定义了所有的necesar函数，并且逐步测试了它们的评估应该可以正常工作，但是我没有成功地操作while中的变量。如何使x，vn， v改变它们的值？我认为我应该像rec循环一样重写，但不能完全确定：
下面是代码的其余部分： http://pastebin.com/Ash3xw6y

 伪代码：
输入：f公式
输出：是，如果f有效
否则不是
开始：
 V =变量集合
从f =>和< => 
 while（V is not empty）
从V 
中选择x V = V  -  {x} 
用f替换f [x-> true]&& f [x-> false] 
尽可能简化f 
如果f用true求值然后返回true 
 else if（not f）is true true then return false 
结束如果
结束而
返回false 
结束
 
类型bexp = V 
 |字符串
 | B的bool 
 |否定bexp 
 |和bexp * bexp 
 |或者是bexp * bexp 
 | bexp * bexp 
 |的Impl eqv of bexp * bexp 
 
 module StringSet = Set.make（String）
 
 let is_valide f = 
 let v = stringset_of_list（ens f []）in （*消除=>和< => *）
让quit_loop = ref false在
中，而不是！ quit_loop 
 do 
 let x = StringSet.choose v in 
 let vn = StringSet.remove xv in 
 if StringSet.is_empty vn = true then quit_loop：= true; 
让h = And（替换x（B true）g，替换x（B false）g）in 
 let j =简化h in 
 if（only_bools j）then 
 if（eval j）then print_stringyes
 else print_stringnot
 done 
  

（ New form ）

 让重言式f = 
让rec tautology1 xvg = 
让h = And（remplace x（B true）g，remplace x（B false）g）in 
 let j =简化h in 
 if（not_bools j）then tautology（ StringSet.reose（StringSet.remove xv）（StringSet.remove xv）j 
 else 
 if（eval1 j）then print_stringyes \\\
else 
 if（eval1（Neg（j ））然后print_stringnot \\\
; 
 in tautology1（StringSet.choose（stringset_of_list（ens f []））（stringset_of_list（ens f []））（elim f）;; 
  




解决方案

whi le 循环属于OCaml中的命令式编程部分。

基本上，你不能修改，而或用于循环或任何地方。 变量是可变的，你需要定义它像 let var = ref ... 。 ref 是关键字mutables。

阅读这两章：

1. https ：//realworldocaml.org/v1/en/html/a-guided-tour.html#imperative-programming


>

---

您可以定义 x，vn，v as ref s，但我猜它会很难看。

我建议你认为你的代码在

由于您没有在这里放置函数 ens 等，所以我无法提供一个示例为你。

I have the following code in OCaml.I have defined all necesar functions and tested them step by step the evalution should work good but I didn't succed to manipulate the variables inside of while.How can I make x,vn,v to change their value?I think I should rewrite the while like a rec loop but can't figure out exactly: Here is the rest of code: http://pastebin.com/Ash3xw6y

Pseudocode: 
  input : f formula
  output: yes if f valid 
           else not
    begin:
        V =set of prop variables
        eliminate from f => and <=>
        while (V is not empty)
           choose x from V
           V =V -{x}
           replace f with f[x->true]&&f[x->false]
            simplify as much as possible f
            if f is evaluated with true then return true 
                 else if (not f) is evaluated true then return false
            end if
           end while
      return false
  end

type bexp = V of 
            | string
            | B of bool
            | Neg of bexp
            | And of bexp * bexp 
            | Or of bexp * bexp
            | Impl of bexp * bexp
            | Eqv of bexp * bexp  

module StringSet=Set.make(String)

let is_valide f=
  let v= stringset_of_list (ens f []) in  (*set of all variables of f *)
  let g= elim f in  (*eliminate => and <=> *)
  let quit_loop=ref false in  
  while not !quit_loop
  do
    let x=StringSet.choose  v in
    let vn=StringSet.remove x v in
    if StringSet.is_empty vn=true then quit_loop:=true;
    let h= And( replace x (B true) g ,replace x (B false) g)in
    let j=simplify h in
    if (only_bools j) then
      if (eval j) then print_string "yes" 
      else print_string "not"
  done

(New form)

   let tautology f =
           let rec tautology1 x v g =     
               let h= And( remplace x (B true) g ,remplace x (B false) g)in
               let j= simplify h in
     if not (only_bools j) then tautology (StringSet.choose (StringSet.remove x v)     (StringSet.remove x v)  j 
                 else 
                   if (eval1 j) then print_string "yes \n "  else
                     if (eval1 (Neg (j)))  then  print_string "not \n";
           in tautology1 (StringSet.choose (stringset_of_list (ens f [])) (stringset_of_list (ens f []))  (elim f);;

解决方案

while loop belongs to imperative programming part in OCaml.

Basically, you can't modify immutable variables in while or for loops or anywhere.

To let a variable to be mutable, you need to define it like let var = ref .... ref is the keyword for mutables.

Read these two chapters:

1. https://realworldocaml.org/v1/en/html/a-guided-tour.html#imperative-programming
2. https://realworldocaml.org/v1/en/html/imperative-programming-1.html

---

You can define x,vn,v as refs, but I guess it will be ugly.

I suggest you think your code in a functional way.

Since you haven't placed functions ens etc here, I can't produce an example refine for u.

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