fixed the problem in translating the standardAnswer from ast to string, so now validator works well

src/components/ProofStepDialog.vue

@@ -77,7 +77,7 @@ export default {
       localVisible: this.visible,
       ruleFunction: null,
       selectedRule: '',
-      standardAnswer: null,
+      standardAnswer: '',
       expressions: [], // parsed expressions
       currentExpression: '',
       answers: [], // original user input string
@@ -108,16 +108,21 @@ export default {
       this.localVisible = newVal;
     },
 
-    closeDialog() {
-      console.log("cancel clicked");
-      console.log(this.statement);
-      console.log(this.ruleFunction);
-      console.log(this.conclusionString);
-      console.log(this.expressions);
-      console.log(this.answers);
-      this.selectedRule = '';
+    clean() {
       this.ruleFunction = null;
+      this.selectedRule = '';
+      this.standardAnswer = '';
+      this.expressions = [];
+      this.currentExpression = '';
+      this.answers = [];
+      this.currentAnswer = '';
+      this.errorMsg = '';
+      this.msg = '';
+    },
+
+    closeDialog() {
       this.localVisible = false;
+      this.clean();
     },
 
     // 新增的方法
@@ -132,7 +137,6 @@ export default {
       if (this.currentAnswer) {
         this.answers.push(this.currentAnswer);
         this.currentAnswer = '';
-        this.errorMsg = '';
       }
     },
 
@@ -177,20 +181,36 @@ export default {
       }
 
       // list of strings
-      this.standardAnswer.forEach(answer => { ast.astsToString(answer); });
+      this.standardAnswer = this.standardAnswer.map(answer => ast.astsToString(answer));
 
       this.standardAnswer.sort();
       this.answers.sort();
 
+      console.log(this.statement);
+      console.log(this.ruleFunction);
+      console.log(this.conclusionString);
+      console.log(this.expressions);
+      console.log(this.answers);
+      
+      console.log("standard answer result:", JSON.stringify(this.standardAnswer, null, 2));
+
       for (let i = 0; i < this.standardAnswer.length; i++) {
+        console.log(this.answers[i]);
+        console.log(this.standardAnswer[i]);
         const output = validator(this.standardAnswer[i], this.answers[i]);
         if (!output[0]) {
-          this.errorMsg = output[1];
+          this.errorMsg = "Incorrect answer in statement " + this.answers[i] + output[1];
           return;
         }
       }
 
       this.msg = 'Correct answer';
+
+      this.selectedRule = '';
+      this.ruleFunction = null;
+      this.expressions = [];
+      this.answers = [];
+      this.standardAnswer = null;
       return;
 
     },