Check for division by zero and some code refactor

Author: TheWeirdDev

source/calcool/expression.d

@@ -73,13 +73,18 @@ class OperatorExpression(string op) : Expression
         }
     }
 
-    private enum str = "left.evaluate()" ~ op ~ "right.evaluate()";
     override real evaluate() {
-        return mixin(str);
+        const rhs = right.evaluate();
+        static if (op == "/") {
+            if (rhs == 0) {
+                throw new ParseException("Devide by zero");
+            }
+        }
+        return mixin("left.evaluate()" ~ op ~ "rhs");
     }
 
     override string toString() @safe const {
-        return str;
+        return left.toString() ~ op ~ right.toString();
     }
 }
 

source/calcool/parser.d

@@ -35,6 +35,7 @@ private:
 
 public:
     Token[] input;
+    private static const syntaxError = new ParseException("Syntax error");
 
     this() {
         lexer = new Lexer();
@@ -83,15 +84,14 @@ public:
             }
 
             if (start && input.length > 0 && input.front().type != TokenType.EOL) {
-                input.length = 0;
-                throw new ParseException("Syntax error");
+                error();
             }
             return left;
 
         } else {
-            input.length = 0;
-            throw new ParseException("Syntax error");
+            error();
         }
+        assert(false);
     }
 
     private Precedence getPrecedence() {
@@ -106,14 +106,18 @@ public:
             } else if (t == TokenType.EOL) {
                 return Precedence.START;
             } else {
-                input.length = 0;
-                throw new ParseException("Invalid syntax");
+                error();
             }
         }
 
         return Precedence.START;
     }
 
+    private void error() {
+        input.length = 0;
+        throw syntaxError;
+    }
+
     void expect(TokenType t) {
         if ((input.length > 0 && input.front().type != t) || input.length == 0) {
             import std.format : format;