Fixed the regular expression - also made the command line robust

Made the command line more robust and fixed the regular expression
to make literal dot using \. instead of . (inadvertent error)

diff --git a/src/main.rs b/src/main.rs
index e25413b..c911ca2 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,5 @@
 use std::io;
+use std::io::Write;
 use regex::Regex;
 
 enum Operator { 
@@ -117,26 +118,39 @@ fn main() {
        // get a line from input and evaluate it 
        let mut expr = String::new ();
        // regular expression to match a number 
-       let match_num = Regex::new (r"^\d+?.*?\d*?$").unwrap ();
+       let match_num = Regex::new (r"^\d+?\.*?\d*?$").unwrap ();
        // loop until a blank line is received  
        loop {
                expr.clear ();  
-               println!("Enter an expression (postfix) (blank to quit): ");
+               print!("evpf>");
+               io::stdout().flush ().expect ("Error flushing!");
                // read a line of text
                io::stdin().read_line (&mut expr).expect ("Error reading line!");
                // trim the text
                let expr = expr.trim ();
-               // quit if the expression is blank
-               if expr == "" { 
+
+               if expr == "q" || expr == "Q" {
+               // quit if the expression is q or Qs 
                        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");
+                       continue;
+               } else if expr == "" {
+               // continue without proceeding
+                       continue;
                }
                
                let res = evaluate (&expr, &match_num);
                if res.is_ok () {
-                       println! ("Result is : {}", res.unwrap());
+                       println! ("Result: {}", res.unwrap());
                }
                else {
                        eprintln! ("Error: {}", res.unwrap_err());
+                       eprintln! ("Type ? or h or H for help");
                }
        }
 }