Add assignment 4

src/assignments/assignment04/context.rs

@@ -0,0 +1,46 @@
+//! Calculator.
+
+use std::collections::HashMap;
+
+use anyhow::*;
+
+use super::syntax::{Command, Expression};
+
+/// Calculator's context.
+#[derive(Debug, Default, Clone)]
+pub struct Context {
+    anonymous_counter: usize,
+    variables: HashMap<String, f64>,
+}
+
+impl Context {
+    /// Creates a new context.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Returns the current anonymous variable counter.
+    pub fn current_counter(&self) -> usize {
+        self.anonymous_counter
+    }
+
+    /// Calculates the given expression.
+    pub fn calc_expression(&self, expression: &Expression) -> Result<f64> {
+        todo!("fill here")
+    }
+
+    /// Calculates the given command.
+    ///
+    /// If there is no variable lhs in the command (i.e. `command.variable = None`), its value should be stored at `$0`, `$1`, `$2`, ... respectively.
+    ///
+    /// # Example
+    ///
+    /// After calculating commad `3 + 5` => Context's variables = `{($0,8)}`
+    ///
+    /// After calculating commad `v = 3 - 2` => Context's variables = `{($0,8),(v,1))}`
+    ///
+    /// After calculating commad `3 ^ 2` => Context's variables = `{($0,8),(v,1),($1,9)}`
+    pub fn calc_command(&mut self, command: &Command) -> Result<(String, f64)> {
+        todo!("fill here")
+    }
+}

src/assignments/assignment04/mod.rs

@@ -0,0 +1,20 @@
+//! Assignment 4: Designing a calculator.
+//!
+//! The primary goal of this assignment is twofold:
+//! (1) understanding the `pest` third-party library from documentations; and
+//! (2) using programming concepts you've learned so far to implement a simple arithmetic calculator.
+//!
+//! For `pest`, read the following documentations (that contain 90% of the solution):
+//! - <https://pest.rs/>
+//! - <https://pest.rs/book/>
+//! - <https://docs.rs/pest/latest/pest>
+//!
+//! For calculator, just reading `syntax.rs` would suffice for you to understand what to do.
+//!
+//! You should fill out the `todo!()` placeholders in such a way that `/scripts/grade-04.sh` works fine.
+//! See `assignment04_grade.rs` and `/scripts/grade-04.sh` for the test script.
+//! Run `/scripts/prepare-submissions.sh` and submit `/target/assignment04.zip` to <https://gg.kaist.ac.kr>.
+
+pub mod context;
+pub mod parser;
+pub mod syntax;

src/assignments/assignment04/parser.rs

@@ -0,0 +1,19 @@
+//! Parser.
+
+use super::syntax::*;
+use anyhow::Result;
+
+#[allow(missing_docs)]
+#[allow(missing_debug_implementations)]
+mod inner {
+    use pest_derive::*;
+
+    #[derive(Parser)]
+    #[grammar = "assignments/assignment04/syntax.pest"]
+    pub(crate) struct SyntaxParser;
+}
+
+/// Parses command.
+pub fn parse_command(line: &str) -> Result<Command> {
+    todo!("fill here")
+}

src/assignments/assignment04/syntax.pest

@@ -0,0 +1,17 @@
+num = @{ int ~ ("." ~ ASCII_DIGIT*)? ~ (^"e" ~ int)? }
+int = { ("+" | "-")? ~ ASCII_DIGIT+ }
+var = { ("$" | ASCII_ALPHA) ~ (ASCII_ALPHA | ASCII_DIGIT)* }
+
+operation = _{ add | subtract | multiply | divide | power }
+    add      = { "+" }
+    subtract = { "-" }
+    multiply = { "*" }
+    divide   = { "/" }
+    power    = { "^" }
+
+expr = { term ~ (operation ~ term)* }
+term = _{ num | var | "(" ~ expr ~ ")" }
+
+command = _{ SOI ~ (var ~ "=")? ~ expr ~ EOI }
+
+WHITESPACE = _{ " " | "\t" }

src/assignments/assignment04/syntax.rs

@@ -0,0 +1,43 @@
+//! Syntax.
+
+/// Command of the form "<expression>" or "<var> = <expression>".
+#[derive(Debug, Clone, PartialEq)]
+pub struct Command {
+    /// Variable (lhs).
+    pub variable: Option<String>,
+    /// Expression (rhs).
+    pub expression: Expression,
+}
+
+/// Binary operators.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BinOp {
+    /// Add.
+    Add,
+    /// Subtract.
+    Subtract,
+    /// Multiply.
+    Multiply,
+    /// Divide.
+    Divide,
+    /// Power.
+    Power,
+}
+
+/// Expression.
+#[derive(Debug, Clone, PartialEq)]
+pub enum Expression {
+    /// Number.
+    Num(f64),
+    /// Variable.
+    Variable(String),
+    /// Binary operation.
+    BinOp {
+        /// Operator.
+        op: BinOp,
+        /// Lhs.
+        lhs: Box<Expression>,
+        /// Rhs.
+        rhs: Box<Expression>,
+    },
+}