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use std::fmt;
use std::fmt::{Debug, Display, Formatter};
use std::str::FromStr;
use winnow::prelude::*;
use winnow::{
ascii::{digit1 as digits, multispace0 as multispaces},
combinator::alt,
combinator::delimited,
combinator::repeat,
token::one_of,
};
#[derive(Debug, Clone)]
pub 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 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 fn expr(i: &mut &str) -> PResult<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)
}
fn term(i: &mut &str) -> PResult<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)
}
fn factor(i: &mut &str) -> PResult<Expr> {
delimited(
multispaces,
alt((digits.try_map(FromStr::from_str).map(Expr::Value), parens)),
multispaces,
)
.parse_next(i)
}
fn parens(i: &mut &str) -> PResult<Expr> {
delimited("(", expr, ")")
.map(|e| Expr::Paren(Box::new(e)))
.parse_next(i)
}
#[test]
fn factor_test() {
let input = "3";
let expected = Ok(("", String::from("Value(3)")));
assert_eq!(factor.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 12";
let expected = Ok(("", String::from("Value(12)")));
assert_eq!(factor.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = "537 ";
let expected = Ok(("", String::from("Value(537)")));
assert_eq!(factor.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 24 ";
let expected = Ok(("", String::from("Value(24)")));
assert_eq!(factor.map(|e| format!("{e:?}")).parse_peek(input), expected);
}
#[test]
fn term_test() {
let input = " 12 *2 / 3";
let expected = Ok(("", String::from("Div(Mul(Value(12), Value(2)), Value(3))")));
assert_eq!(term.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 12 *2 / 3";
let expected = Ok(("", String::from("Div(Mul(Value(12), Value(2)), Value(3))")));
assert_eq!(term.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 2* 3 *2 *2 / 3";
let expected = Ok((
"",
String::from("Div(Mul(Mul(Mul(Value(2), Value(3)), Value(2)), Value(2)), Value(3))"),
));
assert_eq!(term.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 48 / 3/2";
let expected = Ok(("", String::from("Div(Div(Value(48), Value(3)), Value(2))")));
assert_eq!(term.map(|e| format!("{e:?}")).parse_peek(input), expected);
}
#[test]
fn expr_test() {
let input = " 1 + 2 ";
let expected = Ok(("", String::from("Add(Value(1), Value(2))")));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 12 + 6 - 4+ 3";
let expected = Ok((
"",
String::from("Add(Sub(Add(Value(12), Value(6)), Value(4)), Value(3))"),
));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 1 + 2*3 + 4";
let expected = Ok((
"",
String::from("Add(Add(Value(1), Mul(Value(2), Value(3))), Value(4))"),
));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
}
#[test]
fn parens_test() {
let input = " ( 2 )";
let expected = Ok(("", String::from("Paren(Value(2))")));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 2* ( 3 + 4 ) ";
let expected = Ok((
"",
String::from("Mul(Value(2), Paren(Add(Value(3), Value(4))))"),
));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
let input = " 2*2 / ( 5 - 1) + 3";
let expected = Ok((
"",
String::from("Add(Div(Mul(Value(2), Value(2)), Paren(Sub(Value(5), Value(1)))), Value(3))"),
));
assert_eq!(expr.map(|e| format!("{e:?}")).parse_peek(input), expected);
}
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