95 lines
2.2 KiB
Rust
95 lines
2.2 KiB
Rust
use nom::{
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branch::alt,
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bytes::complete::tag,
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character::complete::char,
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character::complete::{digit1 as digit, space0 as space},
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combinator::map_res,
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multi::fold_many0,
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sequence::{delimited, pair},
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IResult,
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};
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// Parser definition
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use std::str::FromStr;
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// We parse any expr surrounded by parens, ignoring all whitespaces around those
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fn parens(i: &str) -> IResult<&str, i64> {
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delimited(space, delimited(tag("("), expr, tag(")")), space)(i)
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}
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// We transform an integer string into a i64, ignoring surrounding whitespaces
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// We look for a digit suite, and try to convert it.
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// If either str::from_utf8 or FromStr::from_str fail,
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// we fallback to the parens parser defined above
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fn factor(i: &str) -> IResult<&str, i64> {
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alt((
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map_res(delimited(space, digit, space), FromStr::from_str),
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parens,
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))(i)
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}
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// We read an initial factor and for each time we find
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// a * or / operator followed by another factor, we do
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// the math by folding everything
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fn term(i: &str) -> IResult<&str, i64> {
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let (i, init) = factor(i)?;
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fold_many0(
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pair(alt((char('*'), char('/'))), factor),
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move || init,
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|acc, (op, val): (char, i64)| {
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if op == '*' {
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acc * val
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} else {
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acc / val
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}
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},
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)(i)
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}
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fn expr(i: &str) -> IResult<&str, i64> {
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let (i, init) = term(i)?;
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fold_many0(
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pair(alt((char('+'), char('-'))), term),
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move || init,
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|acc, (op, val): (char, i64)| {
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if op == '+' {
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acc + val
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} else {
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acc - val
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}
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},
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)(i)
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}
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#[test]
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fn factor_test() {
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assert_eq!(factor("3"), Ok(("", 3)));
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assert_eq!(factor(" 12"), Ok(("", 12)));
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assert_eq!(factor("537 "), Ok(("", 537)));
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assert_eq!(factor(" 24 "), Ok(("", 24)));
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}
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#[test]
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fn term_test() {
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assert_eq!(term(" 12 *2 / 3"), Ok(("", 8)));
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assert_eq!(term(" 2* 3 *2 *2 / 3"), Ok(("", 8)));
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assert_eq!(term(" 48 / 3/2"), Ok(("", 8)));
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}
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#[test]
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fn expr_test() {
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assert_eq!(expr(" 1 + 2 "), Ok(("", 3)));
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assert_eq!(expr(" 12 + 6 - 4+ 3"), Ok(("", 17)));
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assert_eq!(expr(" 1 + 2*3 + 4"), Ok(("", 11)));
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}
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#[test]
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fn parens_test() {
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assert_eq!(expr(" ( 2 )"), Ok(("", 2)));
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assert_eq!(expr(" 2* ( 3 + 4 ) "), Ok(("", 14)));
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assert_eq!(expr(" 2*2 / ( 5 - 1) + 3"), Ok(("", 4)));
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}
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