fix infitite search for prior operator when opening brackets

src/syntaxer.cpp

@@ -2,10 +2,10 @@
 #include "parser.hpp"
 #include "print.h"
 #include "syntaxer.hpp"
+#include <cmath>
 #include <queue>
 #include <stack>
 #include <vector>
-#include <cmath>
 
 namespace Syntax {
 
@@ -606,13 +606,26 @@ static int same_inner_level_ops(const std::vector<Expression::Token>& tv, const
 
 static Expression::Token::Operator get_prior_mop(const std::vector<Expression::Token>& tv, const int location)
 {
-	for (int i = location - 1; i >= 0; i--)
+	for (int i = location - 1, lv = 0; i >= 0; i--)
 	{
-		if (tv[i].t == Expression::Token::OPERATOR
-			&& tv[i].v.o != Expression::Token::OPA
-			&& tv[i].v.o != Expression::Token::CPA)
+		const Expression::Token &t = tv[i];
+
+		if (t.t == Expression::Token::OPERATOR)
 		{
-			return tv[i].v.o;
+			if (t.v.o == Expression::Token::OPA)
+			{
+				lv--;
+
+				if (lv == -2)
+				{
+					// enclosed in another pair of brackets, safe to assume ADD
+					return Expression::Token::ADD;
+				}
+			}
+			else
+			{
+				return t.v.o;
+			}
 		}
 	}