162 lines
3.2 KiB
Rust
162 lines
3.2 KiB
Rust
#[macro_use]
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extern crate nom;
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use nom::{
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branch::alt,
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sequence::{delimited, pair, preceded},
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character::complete::{digit1 as digit, space0 as space},
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bytes::complete::tag
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};
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// Parser definition
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use std::str;
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use std::str::FromStr;
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use self::Operator::*;
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enum Operator {
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Slash,
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Star,
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}
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impl Operator {
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fn to_str(&self) -> &'static str {
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match *self {
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Slash => "/",
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Star => "*",
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}
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}
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}
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// Parse the specified `Operator`.
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named_args!(operator(op: Operator) <&[u8], &[u8]>,
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call!(tag(op.to_str()))
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);
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// We parse any expr surrounded by the tags `open_tag` and `close_tag`, ignoring all whitespaces around those
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named_args!(brackets<'a>(open_tag: &str, close_tag: &str) <&'a[u8], i64>,
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call!(delimited(
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space,
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delimited(tag(open_tag), preceded(space, expr), preceded(space, tag(close_tag))),
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space
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))
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);
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fn byte_slice_to_str<'a>(s: &'a[u8]) -> Result<&'a str, str::Utf8Error> {
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str::from_utf8(s)
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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 brackets parser defined above
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named!(factor<&[u8], i64>, alt!(
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map_res!(
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map_res!(
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call!(delimited(space, digit, space)),
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byte_slice_to_str
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),
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FromStr::from_str
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)
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| call!(brackets, "(", ")")
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)
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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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named!(term <&[u8], i64>, do_parse!(
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init: factor >>
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res: fold_many0!(
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pair!(alt!(call!(operator, Star) | call!(operator, Slash)), factor),
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init,
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|acc, (op, val): (&[u8], i64)| {
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if (op[0] as char) == '*' { acc * val } else { acc / val }
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}
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) >>
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(res)
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)
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);
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named!(expr <&[u8], i64>, do_parse!(
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init: term >>
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res: fold_many0!(
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call!(pair(alt((tag("+"), tag("-"))), term)),
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init,
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|acc, (op, val): (&[u8], i64)| {
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if (op[0] as char) == '+' { acc + val } else { acc - val }
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}
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) >>
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(res)
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)
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);
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#[test]
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fn factor_test() {
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assert_eq!(
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factor(&b"3"[..]),
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Ok((&b""[..], 3))
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);
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assert_eq!(
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factor(&b" 12"[..]),
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Ok((&b""[..], 12))
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);
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assert_eq!(
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factor(&b"537 "[..]),
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Ok((&b""[..], 537))
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);
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assert_eq!(
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factor(&b" 24 "[..]),
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Ok((&b""[..], 24))
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);
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}
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#[test]
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fn term_test() {
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assert_eq!(
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term(&b" 12 *2 / 3"[..]),
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Ok((&b""[..], 8))
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);
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assert_eq!(
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term(&b" 2* 3 *2 *2 / 3"[..]),
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Ok((&b""[..], 8))
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);
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assert_eq!(
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term(&b" 48 / 3/2"[..]),
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Ok((&b""[..], 8))
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);
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}
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#[test]
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fn expr_test() {
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assert_eq!(
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expr(&b" 1 + 2 "[..]),
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Ok((&b""[..], 3))
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);
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assert_eq!(
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expr(&b" 12 + 6 - 4+ 3"[..]),
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Ok((&b""[..], 17))
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);
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assert_eq!(
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expr(&b" 1 + 2*3 + 4"[..]),
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Ok((&b""[..], 11))
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);
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}
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#[test]
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fn parens_test() {
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assert_eq!(
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expr(&b" ( 2 )"[..]),
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Ok((&b""[..], 2))
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);
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assert_eq!(
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expr(&b" 2* ( 3 + 4 ) "[..]),
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Ok((&b""[..], 14))
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);
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assert_eq!(
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expr(&b" 2*2 / ( 5 - 1) + 3"[..]),
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Ok((&b""[..], 4))
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);
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}
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