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use std::collections::HashMap;
use std::iter::Iterator;
use nom::bytes::complete::tag;
use nom::character::complete::alphanumeric1;
use nom::combinator::iterator;
use nom::sequence::{separated_pair, terminated};
use nom::IResult;
fn main() {
let mut data = "abcabcabcabc";
fn parser(i: &str) -> IResult<&str, &str> {
tag("abc")(i)
}
// `from_fn` (available from Rust 1.34) can create an iterator
// from a closure
let it = std::iter::from_fn(move || {
match parser(data) {
// when successful, a nom parser returns a tuple of
// the remaining input and the output value.
// So we replace the captured input data with the
// remaining input, to be parsed on the next call
Ok((i, o)) => {
data = i;
Some(o)
}
_ => None,
}
});
for value in it {
println!("parser returned: {}", value);
}
println!("\n********************\n");
let data = "abcabcabcabc";
// if `from_fn` is not available, it is possible to fold
// over an iterator of functions
let res =
std::iter::repeat(parser)
.take(3)
.try_fold((data, Vec::new()), |(data, mut acc), parser| {
parser(data).map(|(i, o)| {
acc.push(o);
(i, acc)
})
});
// will print "parser iterator returned: Ok(("abc", ["abc", "abc", "abc"]))"
println!("\nparser iterator returned: {:?}", res);
println!("\n********************\n");
let data = "key1:value1,key2:value2,key3:value3,;";
// `nom::combinator::iterator` will return an iterator
// producing the parsed values. Compared to the previous
// solutions:
// - we can work with a normal iterator like `from_fn`
// - we can get the remaining input afterwards, like with the `try_fold` trick
let mut nom_it = iterator(
data,
terminated(
separated_pair(alphanumeric1, tag(":"), alphanumeric1),
tag(","),
),
);
let res = nom_it
.map(|(k, v)| (k.to_uppercase(), v))
.collect::<HashMap<_, _>>();
let parser_result: IResult<_, _> = nom_it.finish();
let (remaining_input, ()) = parser_result.unwrap();
// will print "iterator returned {"key1": "value1", "key3": "value3", "key2": "value2"}, remaining input is ';'"
println!(
"iterator returned {:?}, remaining input is '{}'",
res, remaining_input
);
}