rpn(1): added From trait to CalcType

src/rpn.rs

@@ -50,7 +50,17 @@ use std::{
 	process::ExitCode,
 };
 
-use CalcType::{ Add, Divide, Floor, Modulo, Multiply, Power, Subtract, Val };
+use CalcType::{
+	Add,
+	Divide,
+	Empty,
+	Floor,
+	Modulo,
+	Multiply,
+	Power,
+	Subtract,
+	Val
+};
 
 extern crate sysexits;
 
@@ -67,6 +77,7 @@ enum CalcType {
 	Floor,
 	Modulo,
 	Val(f64),
+	Empty,
 }
 
 #[derive(Debug, Clone)]
@@ -82,25 +93,23 @@ impl fmt::Display for EvaluationError {
 // repeating and it seems this can give it to me
 const PRECISION_MOD: f64 = 0.9 + f64::EPSILON * 100.0;
 
-// str_to_calc_type converts a string to an optional `CalcType`.
-fn str_to_calc_type(string: &str) -> Option<CalcType> {
-	let as_int = string.parse::<f64>();
-	let result = match as_int {
-		Ok(x) => Some(Val(x)),
-		Err(_) => None,
-	};
-
-	if result.is_some() { return result; }
-
-	match string {
-		"+" => Some(Add),
-		"-" | "−" => Some(Subtract),
-		"*" | "×" => Some(Multiply),
-		"/" | "÷" => Some(Divide),
-		"^" => Some(Power),
-		"//" => Some(Floor),
-		"%" => Some(Modulo),
-		_ => None,
+impl From<&str> for CalcType {
+	fn from(value: &str) -> Self {
+		match value {
+			"+" => Add,
+			"-" | "−" => Subtract,
+			"*" | "×" => Multiply,
+			"/" | "÷" => Divide,
+			"^" => Power,
+			"//" => Floor,
+			"%" => Modulo,
+			_ => {
+				match value.parse::<f64>() {
+					Ok(x) => Val(x),
+					Err(_) => Empty,
+				}
+			},
+		}
 	}
 }
 
@@ -119,14 +128,14 @@ fn eval(
 	let toks = input.split(' ').collect::<Vec<&str>>();
 	let mut ops: VecDeque<CalcType> = VecDeque::new();
 
-	for tok in &toks {
-		let x: CalcType = match str_to_calc_type(tok) {
-			Some(x) => x,
-			None => {
+	for tok in toks {
+		let x: CalcType = match CalcType::from(tok) {
+			Empty => {
 				return Err(EvaluationError {
 					message: format!("Invalid token: {}", tok),
 				})
-			}
+			},
+			x => x,
 		};
 
 		match x {