Function chumsky::recursive::recursive

pub fn recursive<'a, I: Clone, O, P: Parser<I, O, Error = E> + 'a, F: FnOnce(Recursive<'a, I, O, E>) -> P, E: Error<I>>(
    f: F
) -> Recursive<'a, I, O, E>

Construct a recursive parser (i.e: a parser that may contain itself as part of its pattern).

The given function must create the parser. The parser must not be used to parse input before this function returns.

This is a wrapper around Recursive::declare and Recursive::define.

The output type of this parser is O, the same as the inner parser.

Examples

#[derive(Debug, PartialEq)]
enum Tree {
    Leaf(String),
    Branch(Vec<Tree>),
}

// Parser that recursively parses nested lists
let tree = recursive::<_, _, _, _, Simple<char>>(|tree| tree
    .separated_by(just(','))
    .delimited_by(just('['), just(']'))
    .map(Tree::Branch)
    .or(text::ident().map(Tree::Leaf))
    .padded());

assert_eq!(tree.parse("hello"), Ok(Tree::Leaf("hello".to_string())));
assert_eq!(tree.parse("[a, b, c]"), Ok(Tree::Branch(vec![
    Tree::Leaf("a".to_string()),
    Tree::Leaf("b".to_string()),
    Tree::Leaf("c".to_string()),
])));
// The parser can deal with arbitrarily complex nested lists
assert_eq!(tree.parse("[[a, b], c, [d, [e, f]]]"), Ok(Tree::Branch(vec![
    Tree::Branch(vec![
        Tree::Leaf("a".to_string()),
        Tree::Leaf("b".to_string()),
    ]),
    Tree::Leaf("c".to_string()),
    Tree::Branch(vec![
        Tree::Leaf("d".to_string()),
        Tree::Branch(vec![
            Tree::Leaf("e".to_string()),
            Tree::Leaf("f".to_string()),
        ]),
    ]),
])));