X-Git-Url: https://harishankar.org/repos/?p=evpf.git;a=blobdiff_plain;f=src%2Fmain.rs;h=d2371937b73204e75fae8da3dc96fba43fbc461e;hp=c911ca230dd8ccd5191f0a585dbd9fa2881fef0e;hb=e12e35ce57fb851e14e6589959c622512a9d1091;hpb=8c424fbdf4baf3e27f63b2526def89ddf4ac1b83

diff --git a/src/main.rs b/src/main.rs
index c911ca2..d237193 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,7 +1,26 @@
 use std::io;
 use std::io::Write;
 use regex::Regex;
+use colored::*;
+use std::env;
 
+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 a postfix expression to evaluate.",
+				 "Example: 4 5 + 12 -",
+				 "Supported operators: +, -, *, /",
+				 "Type q, Q to quit"
+				 ];
+
+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,
@@ -21,13 +40,13 @@ fn get_result (t : &mut Vec<Expression>, op : Operator) -> Result<f32,String> {
 	// 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;
@@ -97,8 +116,7 @@ fn evaluate (expr : &str, match_num : &regex::Regex) -> Result<f32,String> {
 			  }	
 			// 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());
 			}
 		}
 	}
@@ -106,7 +124,7 @@ fn evaluate (expr : &str, match_num : &regex::Regex) -> Result<f32,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;
@@ -114,18 +132,46 @@ fn evaluate (expr : &str, match_num : &regex::Regex) -> Result<f32,String> {
 	}
 }
 
-fn main() {
+// Single command mode - command line arguments mode - evaluate the expression
+// given in the command line and quit
+fn run_command_line (args : &Vec<String>, match_num : &regex::Regex) {
+	let mut expr = String::new ();
+	let mut i = 0;
+	// create the expression string to evaluate
+	for arg in args.iter() {
+		if i > 0 {
+			expr.push_str (&arg);
+			expr.push_str (" ");
+		}
+		i += 1;
+	}
+	// evaluate the result 
+	let res = evaluate (&expr, &match_num);
+	// if Result is OK then print the result in green
+	if res.is_ok () {
+		let restxt = format! ("{}", res.unwrap());
+		println! ("{}", restxt.green ());
+	} else {
+	// print the error in purple
+		let errtxt = format! ("{}: {}", ERROR, 
+										res.unwrap_err());
+		eprintln! ("{}", errtxt.purple ());
+	}
+}
+
+// Interactive mode - display the prompt and evaluate expressions entered into
+// the prompt - until user quits
+fn run_interactive_mode (match_num : &regex::Regex) {
 	// 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 ();
+
 	// loop until a blank line is received	
 	loop {
 		expr.clear ();	
-		print!("evpf>");
-		io::stdout().flush ().expect ("Error flushing!");
+		print!("{}", "evpf>".bold() );
+		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 ();
 
@@ -134,23 +180,49 @@ fn main() {
 			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! ("{}", text.cyan() );
+			}
+
 			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! ("{}", res.unwrap());
+			println! ("{}", restxt.green ());
+		} else {
+		// print the error in purple
+			let errtxt = format! ("{}: {}", ERROR, 
+											res.unwrap_err());
+			eprintln! ("{}", errtxt.purple());
+			eprintln! ("{}", ERROR_HELP.purple());
 		}
 	}
 }
+
+fn main() {
+	// collect the command line arguments - if any 
+	let args : Vec<String> = env::args().collect ();
+	// regular expression to match a number 
+	let match_num = Regex::new (r"^\d+?\.*?\d*?$").unwrap ();
+	
+	if args.len () > 1 {
+	// if arguments are provided run in command line mode - i.e. print the 
+	// result and exit	
+		run_command_line (&args, &match_num);
+		
+	} else {
+		// if arguments are not provided run in interactive mode - 
+		// display a prompt and get the expression 
+		// repeat until the user quits
+		run_interactive_mode (&match_num);
+
+	}
+}