use std::io;
use std::io::Write;
use regex::Regex;
+use ansi_term::Colour;
+use ansi_term::Style;
+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
enum Operator {
ADD,
SUB,
// if nothing - panic with error
let n1 = t.pop ();
if n1.is_none () {
- return Err ("Illegal expression".to_string());
+ return Err (ILLEGAL_EXP.to_string());
}
// pop the stack for the first operand
// if nothing - panic with error
let n2 = t.pop ();
if n2.is_none () {
- return Err ("Illegal expression!".to_string());
+ return Err (ILLEGAL_EXP.to_string());
}
let num1 = n1.unwrap().value;
}
// if word doesn't match either operator or number then panic.
else {
- return Err ("Error parsing expression! \
- Must be a number or operator (+,-,* or /)".to_string());
+ return Err (ERR_PARSING_NOT_MATCH.to_string());
}
}
}
if ops.len () > 1 {
// if the stack has more than one value, it means that the postfix
// expression is not complete - so display the stack status
- return Err ("Postfix expression incomplete!".to_string());
+ return Err (ERR_POSTFIX_INCOMPLETE.to_string());
} else {
// stack has only one item which is the result so display it
let res = ops[0].value;
// loop until a blank line is received
loop {
expr.clear ();
- print!("evpf>");
- io::stdout().flush ().expect ("Error flushing!");
+ print!("{}", Style::new().bold().paint("evpf>"));
+ io::stdout().flush ().expect (ERR_FLUSHING);
// read a line of text
- io::stdin().read_line (&mut expr).expect ("Error reading line!");
+ io::stdin().read_line (&mut expr).expect (ERR_READING_LINE);
// trim the text
let expr = expr.trim ();
break;
} else if expr == "?" || expr == "h" || expr == "H" {
// display help text
- println! ("Type an expression in postfix style to evaluate.");
- println! ("Example: 4 5 + 12 -");
- println! ("Supported operators: +, -, *, /");
- println! ("Type q, Q to quit");
+ for text in HELP_TEXT.iter() {
+ println! ("{}", Colour::Cyan.paint(*text));
+ }
+
continue;
} else if expr == "" {
// continue without proceeding
continue;
}
+ // Evaluate result
let res = evaluate (&expr, &match_num);
+
+ // if Result is OK then print the result in green
if res.is_ok () {
- println! ("Result: {}", res.unwrap());
- }
- else {
- eprintln! ("Error: {}", res.unwrap_err());
- eprintln! ("Type ? or h or H for help");
+ let restxt = format! ("{}: {}", RESULT,
+ res.unwrap());
+ println! ("{}", Colour::Green.paint (restxt));
+ } else {
+ // print the error in purple
+ let errtxt = format! ("{}: {}", ERROR,
+ res.unwrap_err());
+ eprintln! ("{}", Colour::Purple.paint (errtxt));
+ eprintln! ("{}", Colour::Purple.paint (ERROR_HELP));
}
}
}