68 lines
1.8 KiB
Rust
68 lines
1.8 KiB
Rust
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,
|
|
};
|
|
|
|
// Parser definition
|
|
|
|
pub(crate) fn expr(i: &mut &str) -> Result<i64> {
|
|
let init = term.parse_next(i)?;
|
|
|
|
repeat(0.., (one_of(['+', '-']), term))
|
|
.fold(
|
|
move || init,
|
|
|acc, (op, val): (char, i64)| {
|
|
if op == '+' {
|
|
acc + val
|
|
} else {
|
|
acc - val
|
|
}
|
|
},
|
|
)
|
|
.parse_next(i)
|
|
}
|
|
|
|
// We read an initial factor and for each time we find
|
|
// a * or / operator followed by another factor, we do
|
|
// the math by folding everything
|
|
pub(crate) fn term(i: &mut &str) -> Result<i64> {
|
|
let init = factor.parse_next(i)?;
|
|
|
|
repeat(0.., (one_of(['*', '/']), factor))
|
|
.fold(
|
|
move || init,
|
|
|acc, (op, val): (char, i64)| {
|
|
if op == '*' {
|
|
acc * val
|
|
} else {
|
|
acc / val
|
|
}
|
|
},
|
|
)
|
|
.parse_next(i)
|
|
}
|
|
|
|
// We transform an integer string into a i64, ignoring surrounding whitespace
|
|
// We look for a digit suite, and try to convert it.
|
|
// If either str::from_utf8 or FromStr::from_str fail,
|
|
// we fallback to the parens parser defined above
|
|
pub(crate) fn factor(i: &mut &str) -> Result<i64> {
|
|
delimited(
|
|
multispaces,
|
|
alt((digits.try_map(FromStr::from_str), parens)),
|
|
multispaces,
|
|
)
|
|
.parse_next(i)
|
|
}
|
|
|
|
// We parse any expr surrounded by parens, ignoring all whitespace around those
|
|
fn parens(i: &mut &str) -> Result<i64> {
|
|
delimited('(', expr, ')').parse_next(i)
|
|
}
|