rpn(1): code cleanup

src/rpn.rs

@@ -69,9 +69,7 @@ enum CalcType {
 }
 
 #[derive(Debug, Clone)]
-struct EvaluationError {
-	pub message: String,
-}
+struct EvaluationError { pub message: String }
 
 impl fmt::Display for EvaluationError {
 	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
@@ -91,9 +89,7 @@ fn str_to_calc_type(string: &str) -> Option<CalcType> {
 		Err(_) => None,
 	};
 
-	if result.is_some() {
-		return result;
-	}
+	if result.is_some() { return result; }
 
 	match string {
 		"+" => Some(Add),
@@ -132,22 +128,26 @@ fn eval(
 		};
 
 		match x {
-			Add | Divide | Multiply | Power | Subtract | Modulo => {
-				ops.push_back(x)
-			},
 			Val(x_) => stack.push_back(x_),
+			_ => ops.push_back(x),
 		}
 	}
 
 	for op in &ops {
 		match op {
-			Add | Subtract | Multiply | Divide | Power | Modulo => {
+			Val(_) => {
+				return Err(EvaluationError {
+					message: "Unexpected value in the operator stack."
+						.to_string()
+				})
+			},
+			_ => {
 				let x = &stack.pop_back().ok_or(EvaluationError {
 					message: "Stack is empty.".to_string(),
 				})?;
 
 				let y = &stack.pop_back().ok_or(EvaluationError {
-						message: "Stack is empty.".to_string(),
+					message: "Stack is empty.".to_string(),
 				})?;
 
 				match op {
@@ -160,20 +160,13 @@ fn eval(
 					_ => &{},
 				};
 			},
-			Val(_) => {
-				return Err(
-					EvaluationError {
-						message: "Unexpected value in the operator stack."
-							.to_string()
-					}
-				)
-			},
 		};
 	}
 
 	Ok(stack)
 }
 
+// Round a float to the given precision level
 fn round_precise(value: &f64, precision: usize) -> f64 {
 	let multiplier = 10_f64.powi(precision as i32);
 	(value * multiplier).round() / multiplier
@@ -183,6 +176,8 @@ fn main() -> ExitCode {
 	let argv = args().collect::<Vec<String>>();
 	let mut stack = VecDeque::new();
 	let mut buf = String::new();
+	// Set floating-point precision for correcting rounding errors based on
+	// machine epsilon
 	let precision = (-f64::EPSILON.log10() * PRECISION_MOD).ceil() as usize;
 	
 	if argv.get(1).is_none() {
@@ -196,8 +191,7 @@ fn main() -> ExitCode {
 						None => break,
 					};
 
-					let precise = round_precise(val, precision);
-					println!("{}", precise.to_string());
+					println!("{}", round_precise(val, precision).to_string());
 					buf.clear();
 				},
 				Err(err) => {
@@ -215,7 +209,16 @@ fn main() -> ExitCode {
 			.join(" ");
 
 		match eval(&input, stack) {
-			Ok(val) => println!("{}", val.iter().last().unwrap().to_string()),
+			Ok(s) => {
+				stack = s.clone();
+
+				let val = match stack.iter().last() {
+					Some(v) => v,
+					None => return ExitCode::from(0),
+				};
+
+				println!("{}", round_precise(val, precision).to_string())
+			},
 			Err(err) => {
 				eprintln!("{}: {}", argv[0], err.message);
 				return ExitCode::from(EX_DATAERR as u8);