rpn: initial working prototype
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src/rpn.rs
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211
src/rpn.rs
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/*
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* Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*
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* This program is free software: you can redistribute it and/or modify it under
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* the terms of the GNU Affero General Public License as published by the Free
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* Software Foundation, either version 3 of the License, or (at your option) any
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* later version.
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*
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* This program is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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* FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
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* details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see https://www.gnu.org/licenses/.
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*
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* This file incorporates work covered by the following copyright and permission
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* notice:
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*
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* MIT License
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*
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* Copyright (c) 2022 Lilly Cham
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files
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* (the "Software"), to deal in the Software without restriction, including
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* without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or
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* sell copies of the Software, and to permit persons to whom the Software
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* is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included
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* in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
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* NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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* OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
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* USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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use std::{
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collections::VecDeque,
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env::args,
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fmt,
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io::stdin,
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process::ExitCode,
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};
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use CalcType::{ Add, Divide, Multiply, Power, Subtract, Val };
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#[derive(Clone, Copy, PartialEq, PartialOrd, Debug)]
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/// enum CalcType is a type containing operations used in the calculator.
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enum CalcType {
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Add,
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Subtract,
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Multiply,
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Divide,
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Power,
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Val(f64),
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}
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#[derive(Debug, Clone)]
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struct EvaluationError {
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pub message: String,
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}
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impl fmt::Display for EvaluationError {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "{}", self.message)
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}
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}
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/// str_to_calc_type converts a string to an optional `CalcType`.
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fn str_to_calc_type(string: &str) -> Option<CalcType> {
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let as_int = string.parse::<f64>();
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let result = match as_int {
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Ok(x) => Some(Val(x)),
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Err(_) => None,
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};
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if result.is_some() {
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return result;
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}
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match string {
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"+" => Some(Add),
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"-" => Some(Subtract),
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"*" => Some(Multiply),
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"/" => Some(Divide),
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"^" => Some(Power),
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_ => None,
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}
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}
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fn eval(
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input: &str,
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initial_stack: VecDeque<f64>,
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) -> Result<VecDeque<f64>, EvaluationError> {
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let mut stack = initial_stack;
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// Split the input into tokens.
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let toks = input.split(' ').collect::<Vec<&str>>();
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let mut ops: VecDeque<CalcType> = VecDeque::new();
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for tok in &toks {
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let x: CalcType = match str_to_calc_type(tok) {
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Some(x) => x,
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None => {
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return Err(EvaluationError {
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message: format!("Invalid token: {}", tok),
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})
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}
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};
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match x {
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Add | Divide | Multiply | Power | Subtract => ops.push_back(x),
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Val(x_) => stack.push_back(x_),
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}
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}
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for op in &ops {
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match op {
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Add | Subtract | Multiply | Divide | Power => {
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let x = &stack.pop_back().ok_or(EvaluationError {
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message: "Stack is empty.".to_string(),
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})?;
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let y = &stack.pop_back().ok_or(EvaluationError {
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message: "Stack is empty.".to_string(),
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})?;
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match op {
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Add => {
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&stack.push_back(y + x)
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},
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Subtract => {
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&stack.push_back(y - x)
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},
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Multiply => {
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&stack.push_back(y * x)
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},
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Divide => {
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&stack.push_back(y / x)
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},
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Power => {
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let result = x.powf(*y);
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&stack.push_back(result)
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},
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_ => &{},
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};
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},
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Val(_) => {
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return Err(
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EvaluationError {
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message: "Unexpected value in the operator stack.".to_string()
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}
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)
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},
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};
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}
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Ok(stack)
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}
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fn round_precise(value: &f64, precision: usize) -> f64 {
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let multiplier = 10_f64.powi(precision as i32);
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(value * multiplier).round() / multiplier
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}
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fn main() -> ExitCode {
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let argv = args().collect::<Vec<String>>();
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let stack = VecDeque::new();
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let mut buf = String::new();
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let precision = (-f64::EPSILON.log10() * 0.999).ceil() as usize;
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if argv.get(1).is_none() {
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while let Ok(_) = stdin().read_line(&mut buf) {
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match eval(&buf.trim(), stack.clone()) {
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Ok(val) => {
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let precise = round_precise(val.iter().last().unwrap(), precision);
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println!("{}", precise.to_string());
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buf.clear();
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},
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Err(err) => {
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eprintln!("{}: {}", argv[0], err.message);
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return ExitCode::from(1);
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},
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};
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}
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} else {
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let input = argv
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.iter()
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.skip(1)
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.map(|x| x.to_owned())
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.collect::<Vec<String>>()
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.join(" ");
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match eval(&input, stack) {
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Ok(val) => println!("{}", val.iter().last().unwrap().to_string()),
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Err(err) => {
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eprintln!("{}: {}", argv[0], err.message);
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return ExitCode::from(1);
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},
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};
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}
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ExitCode::from(0)
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}
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