+const ILLEGAL_EXP : &'static str = "Illegal Expression";
+const ERR_PARSING_NOT_MATCH : &'static str = "Error parsing expression! \
+ Must be a number or operator (+,-,* or /)";
+const ERR_POSTFIX_INCOMPLETE : &'static str = "Postfix expression incomplete!";
+const ERR_FLUSHING : &'static str = "Error flushing!";
+const ERR_READING_LINE : &'static str = "Error reading line!";
+const HELP_TEXT : [&str ; 4] =
+ ["Type an expression in postfix style to evaluate.",
+ "Example: 4 5 + 12 -",
+ "Supported operators: +, -, *, /",
+ "Type q, Q to quit"
+ ];
+
+const RESULT : &'static str = "Result";
+const ERROR : &'static str = "Error";
+const ERROR_HELP : &'static str = "Type ? or h or H for help";
+
+// Describe an operator - one of add, subtract, multiply or divide