100 lines
2.7 KiB
Rust
100 lines
2.7 KiB
Rust
use std::fmt;
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use std::fmt::{Debug, Display, Formatter};
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use std::str::FromStr;
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use winnow::prelude::*;
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use winnow::Result;
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use winnow::{
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ascii::{digit1 as digits, multispace0 as multispaces},
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combinator::alt,
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combinator::delimited,
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combinator::repeat,
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token::one_of,
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};
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#[derive(Debug, Clone)]
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pub(crate) enum Expr {
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Value(i64),
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Add(Box<Expr>, Box<Expr>),
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Sub(Box<Expr>, Box<Expr>),
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Mul(Box<Expr>, Box<Expr>),
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Div(Box<Expr>, Box<Expr>),
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Paren(Box<Expr>),
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}
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impl Expr {
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pub(crate) fn eval(&self) -> i64 {
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match self {
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Self::Value(v) => *v,
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Self::Add(lhs, rhs) => lhs.eval() + rhs.eval(),
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Self::Sub(lhs, rhs) => lhs.eval() - rhs.eval(),
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Self::Mul(lhs, rhs) => lhs.eval() * rhs.eval(),
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Self::Div(lhs, rhs) => lhs.eval() / rhs.eval(),
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Self::Paren(expr) => expr.eval(),
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}
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}
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}
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impl Display for Expr {
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fn fmt(&self, format: &mut Formatter<'_>) -> fmt::Result {
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use Expr::{Add, Div, Mul, Paren, Sub, Value};
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match *self {
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Value(val) => write!(format, "{val}"),
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Add(ref left, ref right) => write!(format, "{left} + {right}"),
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Sub(ref left, ref right) => write!(format, "{left} - {right}"),
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Mul(ref left, ref right) => write!(format, "{left} * {right}"),
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Div(ref left, ref right) => write!(format, "{left} / {right}"),
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Paren(ref expr) => write!(format, "({expr})"),
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}
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}
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}
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pub(crate) fn expr(i: &mut &str) -> Result<Expr> {
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let init = term.parse_next(i)?;
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repeat(0.., (one_of(['+', '-']), term))
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.fold(
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move || init.clone(),
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|acc, (op, val): (char, Expr)| {
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if op == '+' {
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Expr::Add(Box::new(acc), Box::new(val))
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} else {
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Expr::Sub(Box::new(acc), Box::new(val))
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}
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},
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)
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.parse_next(i)
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}
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pub(crate) fn term(i: &mut &str) -> Result<Expr> {
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let init = factor.parse_next(i)?;
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repeat(0.., (one_of(['*', '/']), factor))
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.fold(
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move || init.clone(),
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|acc, (op, val): (char, Expr)| {
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if op == '*' {
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Expr::Mul(Box::new(acc), Box::new(val))
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} else {
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Expr::Div(Box::new(acc), Box::new(val))
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}
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},
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)
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.parse_next(i)
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}
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pub(crate) fn factor(i: &mut &str) -> Result<Expr> {
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delimited(
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multispaces,
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alt((digits.try_map(FromStr::from_str).map(Expr::Value), parens)),
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multispaces,
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)
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.parse_next(i)
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}
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fn parens(i: &mut &str) -> Result<Expr> {
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delimited("(", expr, ")")
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.map(|e| Expr::Paren(Box::new(e)))
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.parse_next(i)
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}
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