rpn(1): more improvements

src/rpn.rs

@@ -120,14 +120,20 @@ impl Display for CalcType {
 #[derive(Debug, Clone)]
 struct EvaluationError {
 	message: String,
-	code: ExitCode,
+	code: u8,
+}
+
+impl StrError for EvaluationError {
+	fn strerror(&self) -> String {
+		self.message.clone()
+	}
 }
 
 /* I’m no math nerd but I want the highest possible approximation of 0.9
  * repeating and it seems this can give it to me */
 const PRECISION_MOD: f64 = 0.9 + f64::EPSILON;
 
-fn err(argv0: &String, e: std::io::Error, code: Option<u8>) -> ExitCode {
+fn err<T: StrError>(argv0: &String, e: &T, code: Option<u8>) -> ExitCode {
 	eprintln!("{}: {}", argv0, e.strerror());
 	ExitCode::from(code.unwrap_or(1 /* unknown error */))
 }
@@ -150,6 +156,7 @@ fn eval(
 		.rev()
 		.map(|t| CalcType::from(t))
 		.collect();
+
 	let mut ops: VecDeque<CalcType> = VecDeque::new();
 
 	while let Some(n) = toks.pop_back() {
@@ -157,18 +164,15 @@ fn eval(
 			Val(v) => stack.push_back(v),
 			Invalid(i) => {
 				return Err(EvaluationError {
-					message: format!("{}: Invalid token", i),
+					message: format!("{}: invalid token", i),
-					code: ExitCode::from(EX_DATAERR),
+					code: EX_DATAERR,
 				})
 			},
 			op => {
 				ops.push_back(op.clone());
 				oper = true; /* this is an operation */
 
-				let vals = (
+				let vals = (stack.pop_back(), stack.pop_back());
-					stack.pop_back(),
-					stack.pop_back(),
-				);
 
 				if let (Some(x), Some(y)) = vals {
 					match op {
@@ -183,8 +187,8 @@ fn eval(
 					};
 				} else {
 					return Err(EvaluationError {
-						message: format!("{}: Unexpected operation", op),
+						message: format!("{}: unexpected operation", op),
-						code: ExitCode::from(EX_DATAERR),
+						code: EX_DATAERR,
 					})
 				}
 			},
@@ -204,6 +208,7 @@ fn round_precise(value: &f64) -> f64 {
 	(value * multiplier).round() / multiplier
 }
 
+/* print the stack and let the caller know if evaluation should continue */
 fn unstack(stack: VecDeque<f64>, op: bool) -> Result<bool, Error> {
 	if let Some(val) = stack.iter().last() {
 		if !op { return Ok(true); }
@@ -222,7 +227,7 @@ fn main() -> ExitCode {
 	#[cfg(target_os="openbsd")] {
 		let promises = Promises::new("stdio");
 		if let Err(e) = pledge(Some(promises), None) {
-			return err(&argv[0], e, Some(EX_OSERR));
+			return err(&argv[0], &e, Some(EX_OSERR));
 		}
 	}
 
@@ -240,14 +245,16 @@ fn main() -> ExitCode {
 
 		match eval(&input, stack) {
 			Ok(s) => {
+				/* we can ignore the return value of unstack() because we are
+				 * not continually evaluating from stdin */
 				if let Err(e) = unstack(s.0.clone(), s.1.clone()) {
-					return err(&argv[0], e, Some(EX_IOERR));
+					return err(&argv[0], &e, Some(EX_IOERR));
 				}
+
 				return ExitCode::SUCCESS;
-			}
+			},
 			Err(e) => {
-				eprintln!("{}: {}", argv[0], e.message);
+				return err(&argv[0], &e, Some(e.code));
-				return e.code;
 			},
 		};
 	}
@@ -255,23 +262,24 @@ fn main() -> ExitCode {
 	/* else, read from stdin */
 	loop { /* take input until EOF */
 		if let Err(e) = stdin().read_line(&mut buf) {
-			return err(&argv[0], e, Some(EX_IOERR));
+			return err(&argv[0], &e, Some(EX_IOERR));
 		}
 
 		match eval(&buf.trim(), stack) {
 			Ok(s) => {
 				buf.clear();
-				stack = s.0.clone();
+				stack = s.0.clone(); /* out with the old, in with the new */
 
 				match unstack(s.0, s.1) {
 					Ok(b) if b => continue,
 					Ok(_) => break,
-					Err(e) => return err(&argv[0], e, Some(EX_IOERR)),
+					Err(e) => {
+						return err(&argv[0], &e, Some(EX_IOERR))
+					},
 				};
 			},
 			Err(e) => {
-				eprintln!("{}: {}", argv[0], e.message);
+				return err(&argv[0], &e, Some(e.code));
-				return e.code;
 			},
 		};
 	}