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