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