1 use nom::{
2 branch::alt,
3 bytes::complete::tag,
4 character::complete::char,
5 character::complete::{digit1 as digit, space0 as space},
6 combinator::map_res,
7 multi::fold_many0,
8 sequence::{delimited, pair},
9 IResult,
10 };
11
12 // Parser definition
13
14 use std::str::FromStr;
15
16 // We parse any expr surrounded by parens, ignoring all whitespaces around those
parens(i: &str) -> IResult<&str, i64>17 fn parens(i: &str) -> IResult<&str, i64> {
18 delimited(space, delimited(tag("("), expr, tag(")")), space)(i)
19 }
20
21 // We transform an integer string into a i64, ignoring surrounding whitespaces
22 // We look for a digit suite, and try to convert it.
23 // If either str::from_utf8 or FromStr::from_str fail,
24 // we fallback to the parens parser defined above
factor(i: &str) -> IResult<&str, i64>25 fn factor(i: &str) -> IResult<&str, i64> {
26 alt((
27 map_res(delimited(space, digit, space), FromStr::from_str),
28 parens,
29 ))(i)
30 }
31
32 // We read an initial factor and for each time we find
33 // a * or / operator followed by another factor, we do
34 // the math by folding everything
term(i: &str) -> IResult<&str, i64>35 fn term(i: &str) -> IResult<&str, i64> {
36 let (i, init) = factor(i)?;
37
38 fold_many0(
39 pair(alt((char('*'), char('/'))), factor),
40 move || init,
41 |acc, (op, val): (char, i64)| {
42 if op == '*' {
43 acc * val
44 } else {
45 acc / val
46 }
47 },
48 )(i)
49 }
50
expr(i: &str) -> IResult<&str, i64>51 fn expr(i: &str) -> IResult<&str, i64> {
52 let (i, init) = term(i)?;
53
54 fold_many0(
55 pair(alt((char('+'), char('-'))), term),
56 move || init,
57 |acc, (op, val): (char, i64)| {
58 if op == '+' {
59 acc + val
60 } else {
61 acc - val
62 }
63 },
64 )(i)
65 }
66
67 #[test]
factor_test()68 fn factor_test() {
69 assert_eq!(factor("3"), Ok(("", 3)));
70 assert_eq!(factor(" 12"), Ok(("", 12)));
71 assert_eq!(factor("537 "), Ok(("", 537)));
72 assert_eq!(factor(" 24 "), Ok(("", 24)));
73 }
74
75 #[test]
term_test()76 fn term_test() {
77 assert_eq!(term(" 12 *2 / 3"), Ok(("", 8)));
78 assert_eq!(term(" 2* 3 *2 *2 / 3"), Ok(("", 8)));
79 assert_eq!(term(" 48 / 3/2"), Ok(("", 8)));
80 }
81
82 #[test]
expr_test()83 fn expr_test() {
84 assert_eq!(expr(" 1 + 2 "), Ok(("", 3)));
85 assert_eq!(expr(" 12 + 6 - 4+ 3"), Ok(("", 17)));
86 assert_eq!(expr(" 1 + 2*3 + 4"), Ok(("", 11)));
87 }
88
89 #[test]
parens_test()90 fn parens_test() {
91 assert_eq!(expr(" ( 2 )"), Ok(("", 2)));
92 assert_eq!(expr(" 2* ( 3 + 4 ) "), Ok(("", 14)));
93 assert_eq!(expr(" 2*2 / ( 5 - 1) + 3"), Ok(("", 4)));
94 }
95