implemented better text output for the ParserExceptions

src/Parser.java

@@ -84,7 +84,7 @@ public class Parser {
     //parses a list of tokens into a value
     private Optional<Expression> parseValue(List<Lexer.Token> ts) throws ParserException {
         if (ts.isEmpty()) {
-            throw new ParserException("SyntaxError: expected a number");
+            throw new ParserException("RuntimeException: empty token list");
         }
         if (ts.get(0).getType() != Lexer.TokenType.NUMBER) {
             return Optional.empty();
@@ -114,13 +114,13 @@ public class Parser {
     //parses a decimal of a list of tokens & a string
     private Expression parseDecimal(List<Lexer.Token> ts, String data) throws ParserException {
         if(ts.size()<1) {
-            throw new ParserException("SyntaxError: ");
+            throw new ParserException("RuntimeException: empty token list");
         }
         if(ts.get(0).getType() != Lexer.TokenType.SPECIAL) {
-            throw new ParserException("");
+            throw new ParserException("SyntaxException: expected a comma");
         }
         if(ts.get(1).getType() != Lexer.TokenType.NUMBER) {
-            throw new ParserException("");
+            throw new ParserException("SyntaxException: expected a number after a comma");
         }
         Number beforeDot = (Number) parseNumber(data);
         ts.remove(0);